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ArticleOctober 2, 2023

Donor Radii in Rare-Earth Complexes
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Charlene Harriswangler
Charlene Harriswangler
Centro Interdisciplinar de Química e Bioloxía (CICA) and Departamento de Química, Facultade de Ciencias, Universidade da Coruña, A Coruña 15071, Galicia , Spain
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https://orcid.org/0000-0002-0500-9878
Juan C. Frías*
Juan C. Frías
Departamento de Ciencias Biomédicas, Universidad Cardenal Herrera-CEU, CEU Universities, 46115 Valencia, Spain
*Email: [email protected]
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M. Teresa Albelda
M. Teresa Albelda
Instituto de Ciencia Molecular (ICMol), Departamento de Química Inorgánica, Universidad de Valencia, 46980 Paterna, Spain
Departamento de Química Inorgánica, Universidad de Valencia, C/Dr. Moliner 50, 46100 Burjasot, Valencia, Spain
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https://orcid.org/0000-0002-9572-8912
Laura Valencia
Laura Valencia
Departamento de Química Inorgánica, Facultad de Ciencias, Universidade de Vigo, As Lagoas, Marcosende, 36310 Pontevedra, Spain
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Enrique García-España
Enrique García-España
Instituto de Ciencia Molecular (ICMol), Departamento de Química Inorgánica, Universidad de Valencia, 46980 Paterna, Spain
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https://orcid.org/0000-0002-4601-6505
David Esteban-Gómez
David Esteban-Gómez
Centro Interdisciplinar de Química e Bioloxía (CICA) and Departamento de Química, Facultade de Ciencias, Universidade da Coruña, A Coruña 15071, Galicia , Spain
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https://orcid.org/0000-0001-6270-1660
Carlos Platas-Iglesias*
Carlos Platas-Iglesias
Centro Interdisciplinar de Química e Bioloxía (CICA) and Departamento de Química, Facultade de Ciencias, Universidade da Coruña, A Coruña 15071, Galicia , Spain
*Email: [email protected]
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https://orcid.org/0000-0002-6989-9654

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Inorganic Chemistry

Cite this: Inorg. Chem. 2023, 62, 41, 17030–17040

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https://doi.org/10.1021/acs.inorgchem.3c03126

Published October 2, 2023

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Abstract

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We present a set of donor radii for the rare-earth cations obtained from the analysis of structural data available in the Cambridge Structural Database (CSD). Theoretical calculations using density functional theory (DFT) and wave function approaches (NEVPT2) demonstrate that the Ln-donor distances can be broken down into contributions of the cation and the donor atom, with the minimum in electron density (ρ) that defines the position of (3,–1) critical points corresponding well with Shannon’s crystal radii (CR). Subsequent linear fits of the experimental bond distances for all rare earth cations (except Pm³⁺) afforded donor radii (r_D) that allow for the prediction of Ln-donor distances regardless of the nature of the rare-earth cation and its oxidation state. This set of donor radii can be used to rationalize structural data and identify particularly weak or strong interactions, which has important implications in the understanding of the stability and reactivity of complexes of these metal ions. A few cases of incorrect atom assignments in X-ray structures were also identified using the derived r_D values.

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Subjects

Synopsis

Lanthanide-donor distances can be estimated by using crystal radii and donor radii, which were obtained from the simultaneous analysis of a large number of X-ray structures of lanthanide complexes.

Introduction

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The lanthanide series comprises a very coherent group of elements of the periodic table from La (Z = 57) to Lu (Z = 71), whose coordination chemistry is dominated by the trivalent oxidation state. (1) The Ln(III) ions are characterized by their high hydration energies (2,3) and their hard character according to Pearson’s classification. (4) Thus, stable complexation of the Ln(III) ions is generally achieved in aqueous media with hard polyaminopolycarboxilate ligands. The high coordination numbers adopted by these ions (often 8–9) (5,6) make octadentate ligands such as H₅DTPA (7) and H₄DOTA, (8) particularly useful for stable complexation in aqueous media (Chart 1). (9,10) Complexes of these ligands and closely related derivatives are currently used for different biomedical and bioanalytical applications, including the clinical use of Gd(III) complexes in magnetic resonance imaging (11) and a DOTA derivative in radiotherapy using the β-emitter ¹⁷⁷Lu-radionuclide. (12) Some Ln(III) ions are also widely used as luminescent tags for bioanalytical purposes, in particular Eu(III) and Tb(III) complexes, which emit in the visible region of the spectrum. (13,14) Luminescence upconversion has also been recently achieved in molecular Ln(III) complexes. (15,16) Furthermore, the magnetic properties of Ln(III) molecular complexes are currently receiving a great deal of attention due to their behavior as single-molecule magnets. (17,18)

Chart 1. Structures of Ligands Discussed in the Present Work

The applications described above triggered intense research efforts devoted to the preparation of a wide variety of H₅DTPA and H₄DOTA lanthanide derivatives for different purposes. The Cambridge Structural Database (CSD) currently contains around 450 structures of Ln(III) complexes with these families of ligands. The structures reported contain a wide variety of donor groups appended to the cyclic structure of cyclen or the linear diethylenetriamine unit of H₅DTPA. This rich source of structural data provides a unique opportunity to rationalize the coordination chemistry of the Ln(III) ions.

The ionic radii of the Ln(III) ions were defined by Shannon in his seminal paper for coordination numbers (CNs) 8 and 9, and in some cases, 6, 7, and 10. (19) These ionic radii were obtained by analyzing the M–O and M–F distances from oxides and fluorides. Refined values of Shannon’s radii, as well as a new set of ionic radii for uncommon combinations of CNs and oxidation states, were obtained recently using machine learning. (20) Ionic radii for Ln(III) ions derived from EXAFS data in solution are in good agreement with Shannon’s radii. (21) In the case of transition metal ions, ionic radii are also affected by the electronic spin as high- and low-spin configurations are characterized by different radii and covalency. As mentioned previously, the Ln(III) ions are hard Lewis acids according to Pearson’s classification, and the Ln(III)-ligand interactions are essentially determined by electrostatic and steric factors. Thus, the CN and coordination polyhedron in a particular Ln(III) complex are mainly dictated by the nature and topology of the ligand and the size of the metal ion. The lanthanide series is characterized by a smooth contraction in ionic radii on increasing atomic number, which amounts to only ∼15%. (22) As a result, Ln(III) complexes often form an isostructural series of complexes in which the Ln(III)-donor distances progressively decrease across the series. However, abrupt changes in coordination number and coordination polyhedron have also been observed. (23) Nevertheless, the Ln(III) ions certainly comprise the most coherent family of metal ions across the periodic table in relation to their coordination properties. Recent work suggests that a linear variation of Ln-donor distances across the series is more common than a curved dependence. (24,25)

The calculation of Shannon’s effective ionic radii relies on the assumption that interatomic distances can be approximated as the sum of cation and anion radii, which change with the coordination number. Some authors, who argued that it is doubtful that an unambiguous separation of a bond into a cation and an anion part can be reached, have heavily criticized this assumption. (26) Indeed, covalence significantly affects interatomic distances, even in Ln(III) compounds. (27) As a result, ionic radii often do not provide realistic estimates of the size and shapes of ions. (28) In an attempt to circumvent this problem, some authors derived radii from the distribution of electron density, (29−31) which is an observable that can be measured experimentally or calculated using quantum mechanical calculations. Nevertheless, ionic radii remain a very useful tool of widespread use by chemists, material scientists, and mineralogists to rationalize structural data. In the case of covalent compounds, bond lengths could be predicted to a surprisingly good accuracy as the sum of two atomic radii, providing the bond is not too ionic, the corresponding coordination numbers are not very different and the concerning bonds do not have multiple bond character (i.e., bonds involving transition metals and halides). (32−34)

From the perspective of coordination chemistry in aqueous media, most Ln(III) complexes display coordination numbers 8 and 9, though some examples of complexes with coordination numbers 7, 10, and even 11 have been described (Figure 1). Two La(III) complexes with DOTA^4– derivatives containing amide pendants were found to possess CN 10 in the solid state, where solvent molecules and counterions complete the metal coordination environment. (35,36) A DTPA-bis-amide La(III) complex with CN 11 was also reported. (37) All the remaining Ln(III) DOTA^4– and DTPA^5– derivatives show CNs 8 and 9, with a few exceptions of seven-coordinate complexes. The latter are Tb(III), Dy(III), and Er(III) complexes with cyclen-based ligands that contain bulky phenolate pendant arms. (38,39) The relative abundance of CN 8 increases across the lanthanide series as the ionic radius of the metal ion decreases, as would be expected. The concept of the coordination number has also been a matter of debate in some cases. For instance, Ln–OH₂ distances in some Ln(III) DOTA^4– derivatives increase along the second half of the lanthanide series as the size of the metal ion contracts, (40) which led to estimates of noninteger coordination numbers. (41)

Figure 1. Coordination numbers observed in the X-ray structures of the Ln(III) DOTA^4– and DTPA^5– derivatives.

A few structures of lanthanide DOTA^4– derivatives with oxidation states other than +3 have also been also described. Indeed, four structures of eight-coordinate Eu(II) complexes have been reported. Of these structures, three of them are cyclen derivatives containing phosphonate, phosphinate, or amide pendant arms, (42,43) while the last structure is a DTPA^5– complex. (44) Recently, the Ce(IV) complexes of DOTA^4– and the analogue with methylenephosphonate arms (DOTP^8–) were also characterized using X-ray diffraction. (45)

In this work, we sought to take advantage of the large body of structural data reported for Ln(III) DOTA^4– and DTPA^5– derivatives to obtain radii for different donor atom types. These donor radii were obtained from the crystal radii determined by Shannon for CNs 8 and 9, assuming that the Ln(III)-donor distances can be approximated by the sum of Ln(III) and donor radii. We have chosen the set of expanded Shannon’s radii (19,20) for our study due to its widespread use in coordination chemistry. The donor radii reported here will provide key information to analyze the structures of Ln(III) complexes, particularly to identify particularly strong or weak interactions. This may have very important implications in understanding not only the stereochemical properties of Ln(III) complexes but also their stability and reactivity. For instance, particularly weak Ln(III)–O_water interactions, associated with the coordination of a water ligand at a sterically hindered capping position, were correlated to fast water exchange rates, (46,47) an important parameter to be controlled to optimize the efficiency of MRI contrast agents. Long Ln(III)–O distances involving carboxylate groups were also correlated to fast dissociation rates following the acid-catalyzed mechanism. (48) We have also extended our analysis to Y(III) and Sc(III), which together with the lanthanides form the rare earths. The coordination chemistry of Y(III) is very similar to that of the lanthanides (49) and is relevant for the development of radiopharmaceuticals for both imaging and therapy. (50) The coordination chemistry of Sc(III) with polyaminocarboxylate ligands is currently in its infancy, but interest is growing due to the potential of the ⁴⁴Sc-radionuclide in PET imaging, (51) and its potential as a diagnostic match of β^– emitters ¹⁷⁷Lu- and ⁹⁰Y-radionuclides. (12)

Results and Discussion

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Description of the Data Set

The CSD contains crystal data for a large number of lanthanide DOTA^4– and DTPA^5– derivatives, although the number of hits varies significantly across the lanthanide series. A total of 443 structures of DOTA^4– and DTPA^5– derivatives containing Ln(III), Y(III), or Sc(III) ions have been analyzed, among which 83% correspond to DOTA^4– derivatives. The number of DTPA^5– derivatives reported for Gd(III) (31%) is, however, significantly higher than for other lanthanides, a situation that is reflected in the application of these complexes as MRI contrast agents in clinical practice. A few additional structures containing Ln–H and Ln–C bonds have been excluded from this study. The lanthanides with the highest number of hits are Eu (21%), Gd (19%), Yb(10%), and Tb (8%), which reflects the numerous investigations related to the photophysical properties of Eu(III) and Tb(III) complexes and the development of Gd(III)-based contrast agents. These three lanthanides sit at the center of the lanthanide series, with Eu and Tb flanking Gd. Thus, the structural data available are far from being uniformly spread along the series. A significant number of hits were also obtained for Dy(7%). However, very few structures were reported for lanthanides such as Tm (2.3%, 10 hits) and Sc (1.2%, 5 hits, Figure 1).

Bond Distances

O atoms of carboxylate groups (O_C) and amine N atoms (N_A) are the most common donor atoms in the family of complexes analyzed here. The Gd–N_A and Gd–O_C distances for complexes with CN 9 display fairly good Gaussian distributions centered at 2.667 and 2.378 Å, respectively (Figure 2). Thus, Gd–N_A distances are consistently longer than Gd–O_C ones, as noticed previously by analyzing a small set of complexes. (52) This can be attributed, at least in part, to the larger covalent radii of N compared to O. (32) These maxima shift to 2.601 and 2.303 Å for Yb(III) nine-coordinate complexes, which reflects the contraction in bond distances as a result of lanthanide contraction. These shifts of the maxima by ∼0.07 Å are close to that predicted by the corresponding difference in the (revised) Shannon’s radii (0.065 Å). Decreasing the CN from 9 to 8 results in a further shift of the maxima of the Gaussian distributions to 2.555 and 2.264 Å, which represents a contraction of ∼0.05 Å, again close to the variation expected according to the ionic radius (0.057 Å).

The half-width at half height of the Gaussian distributions of Gd–N_A and Gd–O_C distances amounts to 0.123 and 0.094 Å, respectively. The rather broad distribution of Gd–N_A distances is likely related to relatively weak bonds compared with those that involve carboxylate O atoms. This is in line with the lower contribution of amine N atoms compared with carboxylate O atoms to Gd(III) complex stability estimated recently. (10) The analysis of the electron density at the critical points of the concerned bonds also suggests that Gd–N_A bonds are weaker than Gd–O_C bonds. (53) It has been also noted that Ln–N bonds are characterized by rather shallow potential energy surfaces, while Ln-O_C bonds display potential energy surfaces with deeper energy minima. (54) Indeed, some of the Gd–N_A distances shown in Figure 2 are particularly long (>2.9 Å), (55) and one can reasonably associate these distances to weak interactions.

Calculated Electron Densities

The separation of the Ln-donor distances into contributions of the metal ion and the donor atom should ideally reflect the shape of the electron density (ρ) along the bond axis. (30) Chemical bonds are characterized by the presence of (3,–1) critical points (CPs) at coordinate r_c, where the first derivative of the electron density vanishes (∇ρ(r_c) = 0). At this point, the electron density is a minimum along the internuclear axis and a maximum in the plane perpendicular to that axis. A (3,–1) CP is situated on the interatomic surface separating the basins of two neighboring atoms. (56) Thus, prior to the estimation of donor radii, we analyzed the electron density along the Ln-donor axes of the selected systems (Figure 3). For this purpose, we used relativistic all-electron DFT calculations (57,58) using the DKH2 (59) method and the wB97X-D3BJ functional, (60,61) which incorporates empirical dispersion. (62) Basis sets developed specifically for relativistic calculations were used throughout (63,64) (see computational details in the Supporting Information).

Figure 3. Electron densities (ρ) calculated along the Ln-donor paths for different lanthanide complexes with the metal ion placed at the origin. The position of the donor atom corresponds to the maximum of ρ around 2.5 Å; CPs indicated with crosses: (a) [Gd(DTPA)(H₂O)]^2–, CSD code FEPREY; (b) Ln–O_C bonds in [Ln(DTPA)(H₂O)]^2–, Ln = Nd, Yb, CSD codes CUVZOI and KOLGIB); (c) La–O_AM bonds in [La(DOTAM)]³⁺ (CN 8) and [La(DOTAM)(CF₃SO₃)(EtOH)]³⁺ (CN 10), CSD codes PIBGOW and PIRSEO; (d) Eu–O_Phos bonds in [Eu^III(DOTP)]^5– and [Eu^II(DOTP)]^6–, CSD codes AXAMET and ONETEJ. Electron densities were calculated with Multiwfn. (68)

The highest values of ρ are centered on the nuclear positions of the metal ion and, to a lesser extent, on the donor atom. This reflects that most of the electron density sits around the nuclear positions, which act as attractors in the gradient vector field ∇ρ. (65) The value of ρ then decreases along the internuclear axis and reaches a minimum, which corresponds to the position of the (3,–1) CPs. Figure 3a compares the values of ρ along the different Gd-donor bonds in [Gd(DTPA)(H₂O)]^2–. One can notice that the five Gd–O_C distances are quite similar, while more significant differences are observed for the three Gd–N_A distances. All Gd–O_C bonds display very similar positions of the CPs at distances of ∼1.275 Å from the metal ion. The minimum of the electron density deviates significantly from the ionic radius (IR) of Gd(III) (1.107 Å for CN 9). (20) However, the position of the CPs agrees rather well with the crystal radii (CR) of Gd(III) (1.247 Å for CN 9). CR were introduced by Fumi (66) and are considered to correspond more closely to the size of an atom (or ion) in a solid, as pointed out by Shannon in his seminal paper. (19) CR differ from IR by a constant factor, with the former being 0.14 Å longer than the latter. IR were introduced to comply with the 1.40 Å radius for O^2– (CN = 6) proposed by Pauling, (67) while CR use a radius of 1.26 Å for the anion. The positions of the critical points for Gd–N_A and Gd–O_W bonds (O_w, oxygen atom of a water molecule) are further apart from the Gd(III) ion compared with Gd–O_C bonds, deviating from the CR by ca. 0.14 Å. The values of ρ at the CPs are lower for Gd–N_A than Gd–O_C bonds, as observed previously. (53) It is worth noting that calculations performed at the NEVPT2 level provide nearly identical ρ values along the Gd-donor axes (Figure S1).

A comparison of the electron densities along the Ln–O_C bonds for [Ln(DTPA)(H₂O)]^2– complexes (Figure 3b) shows that the position of the CPs shifts toward the Ln(III) ion on proceeding across the series from Nd to Yb, as expected due to the lanthanide contraction. This displacement of the CPs averages 0.129 Å for the five Ln–O_C bonds, a value that is very similar to the shortening observed for the bond distances, at an average of 0.156 Å, and the difference in CR (0.120 Å). This suggests that the Ln–O_C bonds can be broken down into contributions of the metal ion radius and the radius of the donor atom. The positions of the CPs are in very good agreement with those marked by the CR. Similar conclusions can be drawn by analyzing the Ln–N_A bonds (Figure S2).

IR and thus CR are defined as specific coordination numbers. To test whether the shape of ρ across the bond path supports this assumption, we carried out calculations on the [La(DOTAM)]³⁺ and [La(DOTAM)(CF₃SO₃)(EtOH)]³⁺ complexes, in which the La(III) ions display CNs 8 and 10, respectively (Figure 3c). Calculations evidence that the CPs characterizing the La–O_AM bonds (O_AM = amide oxygen atom) are indeed affected by the CN, with the minima obtained for CN 10 (∼1.371 Å) and 8 (∼1.320 Å), correlating well with the corresponding CR (∼1.411 and 1.301 Å, respectively).

The size of a metal ion is obviously affected by its charge. The coordination chemistry of the rare earths is largely dominated by the trivalent oxidation state. However, complexes of Ce(IV) and Eu(II) with DOTA⁴^– and DTPA⁵^– derivatives were characterized by using X-ray diffraction. The electron densities calculated for the Eu–O_PHOS bonds in [Eu^III(DOTP)]^5– and [Eu^II(DOTP)]^6– show that the position of the CPs shifts according to what would be expected considering the CR of Eu(II) (1.389 Å) and Eu(III) (1.206 Å) and the average Eu–O_PHOS distances (2.573 and 2.325 Å, respectively). A similar conclusion can be reached by analyzing the [Ce^III(DOTA)(H₂O)]⁻ and [Ce^IV(DOTA)(H₂O)] systems (Figure S3).

The results of our calculations support that the Ln-donor bonds can be indeed divided into a contribution from the metal ion, which can be approximated by CR, and a contribution from the donor atom. This approach has of course some limitations, as the size of the metal ion determined by the electron density changes depending on the nature of the donor atom, as illustrated in Figure 3a. However, this effect is still relatively small (∼0.12 Å) compared with the overall bond distance. We also note that the weak Ln-N_A bonds are characterized by rather shallow minima, so that the position of the CP and that marked by the CR are characterized by similar values of ρ. We also note that the coordination geometry is likely to have a minor effect on the position of the CPs, as evidenced by the results obtained for the capped square antiprismatic (SAP) and capped twisted square antiprismatic (TSAP) isomers of [Ce^III(DOTA)(H₂O)]⁻ (Figure S4).

Donor Radii

Having shown that the Ln-donor distances can be reasonably separated into metal ion and donor contributions, we sought to estimate radii for different donor groups commonly present in DOTA^4– and DTPA^5– derivatives using the following expression:

d_{Ln - D} = r_{D} + {CR}_{Ln}

(1)

where d_Ln–D represents the Ln³⁺-donor distance, r_D is the radius of a given donor atom, and CR_Ln is the crystal radius of the Ln³⁺ ion. In our analysis, we used CR obtained after adding a value of 0.14 Å to the refined Shannon’s radii reported recently. Thus, a plot of d_Ln–D versus CR_Ln should provide a linear trend whose intercept corresponds to r_D when the slope is fixed to 1. Figure 4 provides examples of these plots as well as the linear fits of the data. Since CR take different values depending on the coordination number, one needs to establish the coordination number a priori in each case. For this work, we assumed that the coordination number is defined by the number of donor atoms within 3.0 Å distance from the metal center. This rather long threshold was chosen to incorporate all donor atoms involved in metal ion coordination into the analysis, including those providing weak interactions, to obtain a truly representative value of the donor radius. All donor atoms within this threshold form a bond with the lanthanide according to Bader’s postulate that a bond between a pair of atoms exists if a (3,–1) CP is present along the internuclear axis. Thus, the CN of the Ln(III) ion equals the number of (3,–1) CPs in its surroundings. Calculations performed on the [Er(DOTMA)(H₂O)]⁻ complex, which contains a long Er–OH₂ distance of 2.732 Å, confirm the presence of a (3,–1) CP along the Er–O internuclear axis (Figure S5).

Figure 4. Plot according to eq 1 of bond distances (d_Ln–D) involving amine N atoms versus crystal radii.

The advantage of this analysis is that the r_D values are obtained from the simultaneous fit of bond distances observed for all rare-earth complexes, excluding radioactive Pm. Thus, this approach provides a clear advantage over the simple analysis of bond distances for a particular Ln³⁺ ion, Sc³⁺ or Y³⁺. Indeed, this approach allows for accumulating enough bond distance data for a specific donor atom, even if none or a few values are available for specific Ln³⁺ ions. Furthermore, the fitted r_D values are universally valid for all earth rare cations in any oxidation state, with the only limitation being having reliable CR_Ln data. This provides a very useful tool to analyze complexes with metal ions (i.e., Tm³⁺ and Sc³⁺) or oxidation states (Eu²⁺ and Ce⁴⁺), for which limited structural data are currently available.

Figure 4 presents an example of a fit according to eq 1 for amine N atoms. The linear trend evidences that on average, Ln-donor distances decrease with the decreasing CR of the rare earth, as expected due to the lanthanide contraction. The points in this plot are aligned in 38 vertical lines, each representing a value of CR_Ln, which varies depending on the rare-earth element, its oxidation state, and coordination number. The lowest value of CR_Ln corresponds to Sc³⁺ with CN = 8 (1.011 Å), while the upper limit is given by La³⁺ with CN = 11 (1.459 Å). Linear plots for other donor atoms are shown in Figures S6–S13). The linear fits of the data afforded the r_D values listed in Table 1.

Table 1. Donor Radii (r_D) and Line Widths (Δd_1/2) and Centers (x₀) of the Gaussian Distributions for Rare-Earth Complexes^a

	r_D (Å)^c	Δd_1/2 (Å)	x₀ (Å × 10³)
N_AM	1.425 ± 0.001	0.097	–7.58
O_C	1.132 ± 0.001	0.071	–3.62
O_A	1.130 ± 0.002	0.062	–10.2
Cl	1.451 ± 0.014	^b	^b
F	0.915 ± 0.008	^b	^b
O_PO3	1.114 ± 0.004	0.067	–1.82
O_PRO2	1.106 ± 0.002	0.077	–0.44
N_PY	1.329 ± 0.003	0.053	–4.71
O_Tf	1.183 ± 0.007	^b	^b
O_W	1.231 ± 0.004	0.123	–26.3
O_OH	1.157 ± 0.006	0.058	–2.51

^{^a}

N_AM, amine nitrogen; O_C, carboxylate oxygen; O_A, amide oxygen; Cl, chloride anion; F, fluoride anion; O_PO3, phosphonate oxygen; O_PRO2, phosphinate oxygen; N_PY, pyridine nitrogen; O_Tf, Triflate oxygen; O_W, water oxygen; O_OH, alcohol oxygen.

^{^b}

The limited number of data available prevented accurate Gaussian fitting.

^{^c}

These values can be also used in combination with IR by adding 0.14 Å to the corresponding donor radius. The errors correspond to the standard deviations of the linear fits (see text).

The linear plot obtained for chloride deserves further comment (Figure 5). In spite of the rather limited number of data available for chloride, the observed distances fall within the approximate range of 2.6–2.8 Å, with the exception of two [Eu(L^py)Cl]³⁺ complexes reported by Wada, (69) in which Eu–Cl distances of ∼2.2 Å were reported (orange circles in Figure 5, L^py = 1,4,7,10-tetrakis(pyridin-2-ylmethyl)-1,4,7,10-tetraazacyclododecane, Chart 1). These Eu–Cl distances are, however, within the range expected for Eu–F terminal bonds. The same work reports complexes with Eu–Cl distances of 2.73–2.75 Å. The two complexes with extremely short Eu–Cl bonds were isolated and crystallized as salts of PF₆^– and BF₄^–, which made us suspect that a F atom was assigned incorrectly to a chloride atom. It is worth noting that terminal Ln–F bonds are significantly shorter than bridging F–Ln–F bonds. (64) Thus, the value of r_D reported in Table 1 (and Figure 5) for fluoride was obtained from data for Ln–F bonds involving terminal fluoride coordination.

Figure 5. Plots according to eq 1 of bond distances (d_Ln–D) involving chloride (green circles) and fluoride (blue circles). The orange circles correspond to distances erroneously assigned to Ln–Cl bonds instead of Ln–F bonds (see test).

The extremely short Ln–Cl distances reported by Wada prompted us to prepare and crystallize the complex. Both the ligand and the Eu(III) complex were prepared following reported procedures, (69,70) using the chloride salt. Addition of KPF₆ to an aqueous solution of the complex afforded single crystals with the formula [Eu(L^py)(H₂O)](PF₆)₃·2H₂O. The [Eu(L^py)(H₂O)]³⁺ cation contains a coordinated water molecule with a Eu–O_W distance of 2.378(7) Å, rather than a chloride or fluoride anion (Figure 6). This distance is somewhat shorter than that estimated from the values of r_D and crystal radius (2.49 Å), which is expected considering the positive charge of the complex. (71) Interestingly, the crystal data can also be refined satisfactorily assuming that the ligand present in the apical position is a chloride or a fluoride anion. The refinement of the structure with these incorrect atom assignments yields very similar R1 and wR2 factors (Table S2), and no major (A type) alerts in the checkcif reports. Thus, most likely, the structures reported by Wada contain a Eu–F rather than a Eu–Cl bond.

Figure 6. Structure of the [Eu(L^py)(H₂O)]³⁺ cation present in the crystals of [Eu(L^py)(H₂O)](PF₆)₃·2H₂O.

Figure 7 shows the difference between experimental and calculated bond distances (Δd) of amine and carboxylate donor atoms obtained for three rare-earth cations representative of large (La³⁺), medium (Gd³⁺), and small (Yb³⁺) cations. The values of Δd display rather good Gaussian distributions with maxima close to Δd = 0. The fact that the maximum of the Gaussian distribution does not drift across the lanthanide series provides confidence in the reliability of our approach. One can notice that Ln–O_C bonds are characterized by narrower distributions than Ln–N_A bonds, as mentioned above. Most of the calculated bond distances fall within the −0.1 Å < Δd < 0.1 Å window (<90%). Furthermore, the bonds with the largest deviations are associated with unusual coordination features. For instance, the La–O_C bonds characterized by Δd = 0.271 Å correspond to a dinuclear La³⁺ complex, with CN 11 and carboxylate bridges coordinating through a μ²-η²:η¹ mode. (37,72) The La–O_C distances with Δd = ∼ 0.17 Å also correspond to bridging carboxylate groups coordinating in a μ²-η² mode. (73)

Figure 7. Histograms showing the differences between experimental and calculated bond distances involving the Ln(III) ion and carboxylate O donor atoms and amine N atoms (Δd = d^exp – d^cal, with d^cal = r_D + CR_Ln).

The values of Δd obtained for all rare-earth cations and nine different donor atoms are shown in Figure 8. The histograms were subsequently fitted to Gaussian functions, which provided the fitted values of the center (x₀) and the width at half height (Δd_1/2). For some donor atoms (F, Cl, and O_Tf), the limited number of data prevented accurate Gaussian fitting. All fitted Gaussian functions show very small x₀ values, indicating that the Gaussian functions are centered at d_Ln–D ∼ r_D + CR_Ln (Δd ∼ 0). The absolute values of x₀ are generally equal to or lower than 0.01 Å, with the exception of the Ln–O_w bonds, for which x₀ = −0.026 Å. The Ln–O_w bonds are also characterized by a rather broad distribution, with Δd_1/2 = 0.123 Å (Table 1).

Figure 8. Histograms showing the differences between experimental and calculated bond distances involving the rare-earth ion and different donor atoms (Δd = d^cal – d^exp, with d^cal = r_D + CR_Ln). Histograms were constructed from data obtained for all rare-earth cations. The numbers within parentheses indicate the number of data points.

We note that the histograms are not perfectly symmetrical, showing a hump on the positive side. This implies that the number of distances with positive deviations (d_Ln–D > r_D + CR_Ln) exceeds those with negative Δd values. The shape of the histograms resembles, to a certain extent, that of a potential energy curve associated with a bond distance, which is often described by a Morse function. (74) This suggests that shortening the Ln-donor distance beyond the value of x₀ provokes a steeper increase in energy than weakening the Ln-donor interaction. The asymmetry of the histogram is particularly evident in the Ln–O_W bonds, for which positive deviations of Δd of up to 0.35 Å are observed (Figure 8). This is expected, as most donor atoms are incorporated into the macrocyclic or linear scaffold of the ligand. In this situation, the spread of Δd values is reduced, as increasing a d_Ln–D distance above a certain value will weaken the interaction with the neighboring donor atoms. Water generally acts as a monodentate ligand, and thus, the Ln–O_W distance can vary significantly without a significant energy cost. In fact, rare-earth complexes present in solution with different hydration numbers are rather common. (75−78) Extremely long Ln–O_W distances in DOTA derivatives have been also correlated with fast exchange rates of the coordinated water molecule. (40,41) This has been explained by the fact that a weak Ln–O_W interaction reduces the energy cost to reach the transition state responsible for the dissociative water exchange mechanism. (47) Water molecules occupying sterically demanding capping positions in the coordination polyhedron display particularly fast water exchange rates, a phenomenon that has been defined as the labile capping bond effect. (46,79) The large steric demand of capping positions is also evidenced in the structures of nine-coordinate Eu(III) and Er(III) DO3A derivative complexes containing a phenanthroline pendant. (80) The N atom of the phenanthroline unit at the capping position is characterized by long Ln–N distances with Δd = +0.185 and 0.197 Å for Eu(III) and Er(III), respectively. Conversely, the pyridyl donor atom at the upper plane of the SAP coordination polyhedron is characterized by a short distance (Δd = −0.066 and −0.092 Å for Eu(III) and Er(III), respectively).

The values of r_D obtained from the linear fits of the data according to eq 1 show that donor radii vary significantly for the different donor atom types. Among the groups containing O donor atoms, phosphinate and phosphonate atoms present the smallest r_D values, followed closely by carboxylate and amide atoms, which present identical r_D values within statistical error. Alcohol donor groups present a slightly larger r_D value than carboxylates and amides, while water is characterized by the largest r_D value among all the donor groups considered here. An oxygen atom of a triflate anion presents an r_D value intermediate between those of water and alcohol O atoms. The r_D values involving N donor atoms are higher than those of Ln-O bonds, as would be expected according with the covalent radii of O and N. (32) The same reason explains the very short r_D value obtained for fluoride and the long r_D value obtained for chloride. Among the N donor atoms considered here, amine N atoms are characterized by a significantly longer r_D value than that of pyridine, with the latter also showing a narrower distribution.

A relatively small number of X-ray structures analyzed here contained protonated carboxylate groups (13 data points), which display Δd values in the range of 0.010–0.115 Å. (81−85) Thus, protonation of a carboxylate group provokes only a slight increase of the Ln–O_c bond distances. Protonation of coordinated phosphonate groups does not have any significant effect (−0.072 < Δd < 0.044 Å). (45,86,87)

It is worth noting that the r_D values do not correlate with the contributions of these donor groups to complex stability. For instance, we have estimated recently that phosphonate groups contribute with Δlog K = 5.0 units to the stability of a Gd³⁺ complex, while the contribution of a phosphinate group is only 1.9 log K units. (10) However, both donor groups display virtually identical r_D values.

The r_D values reported here allow for the estimation of a typical Ln-donor distance for any rare-earth complex. This is very useful, as there is no set of radii available for donor atoms that can provide good estimates of lanthanide-donor bond distances. The crystal CR reported by Shannon do not provide good estimates of Ln(III)-donor distances in polyaminopolycarboxylate complexes. Furthermore, Shannon defined different CR for the oxide anion depending on the coordination number (1.21–1.28 Å). (19) The value of 1.21 Å (for CN 2) is 0.08 Å longer than the donor radius of a carboxylate oxygen atom (1.132 Å). Differences even increase when taking CR for higher coordination numbers. The deviation is significantly larger for a phosphonate or phosphinate (up to 0.1 Å). This is a huge difference, as it roughly corresponds to the distance between the center and the tail of the Gaussian distribution (Figure 8). The situation is not better when van der Waals radii are used for neutral donors. Bondi’s radius (88) for a N atom of 1.55 Å is significantly larger than the donor radius estimated in our work for an amine donor (1.425 Å) and deviates even more from that of a pyridyl donor (1.329 Å). The situation worsens for neutral O atoms, as the donor radii of amide (1.130 Å) and water (1.231 Å) differ by 0.1 Å, and the van der Waals radius of O is much larger (1.52 Å). (88,89) Thus, it is clear that there is currently no reliable set of radii that allows for the calculation of Ln-donor distances with reasonable accuracy.

In order to test the usefulness of donor radii to predict bond lengths in lanthanide complexes based on platforms other than H₄DOTA and H₅DTPA, the bond distances of complexes based on the 18-membered macrocycle PYAN (i.e., H₄PYTA, Chart 1) were analyzed. (90−94) These systems were chosen because of the presence of pyridine groups in the macrocyclic backbone, the high coordination numbers observed for most rare-earth complexes (typically CN 10), and the availability of structures for many of the rare-earths. A plot of the measured bond distances against the distances calculated using the donor radii (Figure S14) shows a reasonably good distribution around the identity function.

Conclusions

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This work has established a straightforward approach to derive donor radii for complexes of rare-earth cations, providing a tool to estimate Ln-donor distances (including Y and Sc) regardless of the nature of the rare-earth cation and its oxidation state. Our approach relies on separating the Ln-donor distances into contributions from the cation, approximated by the CR, and the donor atom. Theoretical calculations provide support for this approach, at least for complexes with polyaminopoly(carboxylate) ligands used for stable complexation in aqueous media. The rare-earth cations are particularly well-suited for the analysis presented here, as they represent the most coherent series of elements within the periodic table in terms of their chemical properties.

The work presented in this contribution provides a rich source of data that will be very helpful in analyzing the structural data of rare-earth complexes. For instance, particularly strong or weak interactions can be easily identified, providing foundations for the interpretation of thermodynamic and kinetic data. Additionally, these radii can be very helpful in crystallographic analysis to prevent incorrect atom assignments. The approach presented here can be easily applied to other donor groups, which were excluded here due to the scarcity of data for these donors in our data set (i.e., phenol, ether oxygen atoms, etc.). Historically, IR have served as a very useful tool for geochemists, mineralogists, chemists, and material scientists to rationalize structural data. However, our results indicate that CR provide a better estimate of lanthanide ion size than IR. Therefore, we recommend the use of CR for the rationalization of structural data of Ln(III) compounds and possibly of other metal ions.

Supporting Information

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The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.inorgchem.3c03126.

Computational details, crystallographic data (CCDC 2266985), additional plots showing calculated electron densities, linear fits according to eq 1, and bond distances used in this work with CSD codes (PDF)

ic3c03126_si_001.pdf (2.22 MB)

Accession Codes

CCDC 2266985 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

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Author Information

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Corresponding Authors
- Juan C. Frías - Departamento de Ciencias Biomédicas, Universidad Cardenal Herrera-CEU, CEU Universities, 46115 Valencia, Spain; Email: [email protected]
- Carlos Platas-Iglesias - Centro Interdisciplinar de Química e Bioloxía (CICA) and Departamento de Química, Facultade de Ciencias, Universidade da Coruña, A Coruña 15071, Galicia , Spain; https://orcid.org/0000-0002-6989-9654; Email: [email protected]
Authors
- Charlene Harriswangler - Centro Interdisciplinar de Química e Bioloxía (CICA) and Departamento de Química, Facultade de Ciencias, Universidade da Coruña, A Coruña 15071, Galicia , Spain; https://orcid.org/0000-0002-0500-9878
- M. Teresa Albelda - Instituto de Ciencia Molecular (ICMol), Departamento de Química Inorgánica, Universidad de Valencia, 46980 Paterna, Spain; Departamento de Química Inorgánica, Universidad de Valencia, C/Dr. Moliner 50, 46100 Burjasot, Valencia, Spain; https://orcid.org/0000-0002-9572-8912
- Laura Valencia - Departamento de Química Inorgánica, Facultad de Ciencias, Universidade de Vigo, As Lagoas, Marcosende, 36310 Pontevedra, Spain
- Enrique García-España - Instituto de Ciencia Molecular (ICMol), Departamento de Química Inorgánica, Universidad de Valencia, 46980 Paterna, Spain; https://orcid.org/0000-0002-4601-6505
- David Esteban-Gómez - Centro Interdisciplinar de Química e Bioloxía (CICA) and Departamento de Química, Facultade de Ciencias, Universidade da Coruña, A Coruña 15071, Galicia , Spain; https://orcid.org/0000-0001-6270-1660
Author Contributions
The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript.
Notes
The authors declare no competing financial interest.

Acknowledgments

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This research was funded by the Spanish Ministry for Science and Innovation, the National Research Agency and FEDER funds from the EU (grants PID2019-104626GB-I00, PID2019-110751RB-I00, and RED2022-134091-T), Xunta de Galicia (ED431B 2020/52), and the Conselleria de Innovación, Universidades, Ciencia y Sociedad Digital of the Generalitat Valenciana (PROMETEO Grant CIPROM/2021/030). This contribution is also based upon work from COST Action CA18202, NECTAR - Network for Equilibria and Chemical Thermodynamics Advanced Research, supported by COST (European Cooperation in Science and Technology). C.H. thanks Ministerio Ciencia e Innovación (Grant PRE2020-092888) for funding her PhD contract. The authors also thank Centro de Supercomputación de Galicia (CESGA) for providing the supercomputing facilities.

References

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Wahsner, J.; Gale, E. M.; Rodríguez-Rodríguez, A.; Caravan, P. Chemistry of MRI Contrast Agents: Current Challenges and New Frontiers. Chem. Rev. 2019, 119 (2), 957– 1057, DOI: 10.1021/acs.chemrev.8b00363
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Chemistry of MRI Contrast Agents: Current Challenges and New Frontiers
Wahsner, Jessica; Gale, Eric M.; Rodriguez-Rodriguez, Aurora; Caravan, Peter
Chemical Reviews (Washington, DC, United States) (2019), 119 (2), 957-1057CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
A review. Tens of millions of contrast-enhanced magnetic resonance imaging (MRI) exams are performed annually around the world. The contrast agents, which improve diagnostic accuracy, are almost exclusively small, hydrophilic gadolinium(III) based chelates. In recent years concerns have arisen surrounding the long-term safety of these compds., and this has spurred research into alternatives. There has also been a push to develop new molecularly targeted contrast agents or agents that can sense pathol. changes in the local environment. This comprehensive review describes the state of the art of clin. approved contrast agents, their mechanism of action, and factors influencing their safety. From there we describe different mechanisms of generating MR image contrast such as relaxation, chem. exchange satn. transfer, and direct detection and the types of mols. that are effective for these purposes. Next we describe efforts to make safer contrast agents either by increasing relaxivity, increasing resistance to metal ion release, or by moving to gadolinium(III)-free alternatives. Finally we survey approaches to make contrast agents more specific for pathol. either by direct biochem. targeting or by the design of responsive or activatable contrast agents.
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Kostelnik, T. I.; Orvig, C. Radioactive Main Group and Rare Earth Metals for Imaging and Therapy. Chem. Rev. 2019, 119 (2), 902– 956, DOI: 10.1021/acs.chemrev.8b00294
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Radioactive Main Group and Rare Earth Metals for Imaging and Therapy
Kostelnik, Thomas I.; Orvig, Chris
Chemical Reviews (Washington, DC, United States) (2019), 119 (2), 902-956CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
Radiometals possess an exceptional breadth of decay properties and have been applied to medicine with great success for several decades. The majority of current clin. use involves diagnostic procedures, which use either positron-emission tomog. (PET) or single-photon imaging to detect anat. abnormalities that are difficult to visualize using conventional imaging techniques (e.g., MRI and X-ray). The potential of therapeutic radiometals has more recently been realized and relies on ionizing radiation to induce irreversible DNA damage, resulting in cell death. In both cases, radiopharmaceutical development has been largely geared toward the field of oncol.; thus, selective tumor targeting is often essential for efficacious drug use. To this end, the rational design of four-component radiopharmaceuticals has become popularized. This Review introduces fundamental concepts of drug design and applications, with particular emphasis on bifunctional chelators (BFCs), which ensure secure consolidation of the radiometal and targeting vector and are integral for optimal drug performance. Also presented are detailed accounts of prodn., chelation chem., and biol. use of selected main group and rare earth radiometals.
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Bünzli, J.-C. G. Lanthanide Luminescence for Biomedical Analyses and Imaging. Chem. Rev. 2010, 110 (5), 2729– 2755, DOI: 10.1021/cr900362e
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Lanthanide Luminescence for Biomedical Analyses and Imaging
Bunzli, Jean-Claude G.
Chemical Reviews (Washington, DC, United States) (2010), 110 (5), 2729-2755CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
A review. This review addresses the problematics of lanthanide luminescent bioprobes (LLB) from the standpoint of their photophys. and biochem. properties; a broad overview of the various applications in which LLBs have been applied is given.
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Bünzli, J.-C. G. On the Design of Highly Luminescent Lanthanide Complexes. Coord. Chem. Rev. 2015, 293–294, 19– 47, DOI: 10.1016/j.ccr.2014.10.013
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On the design of highly luminescent lanthanide complexes
Bunzli, Jean-Claude G.
Coordination Chemistry Reviews (2015), 293-294 (), 19-47CODEN: CCHRAM; ISSN:0010-8545. (Elsevier B.V.)
Presently, phosphors and luminescent materials for lighting, telecommunications, displays, security inks and marking, as well as for probes in biosciences represent one third of the total value of the lanthanides used worldwide. If optical glasses and laser materials are added, this figure is close to 40%, explaining the large interest that the scientific community is devoting to such materials. The present review focuses on the design of highly luminescent lanthanide complexes and discusses all aspects needing optimization. Ref. is made to the mastering of the various energy migration processes in luminescence sensitization by org. ligands, to minimizing non-radiative deactivation mechanisms, as well as to other parameters such as the radiative lifetime, the refractive index, and the benefit of inserting luminescent complexes into inorg.-hybrid structures. Comparative tables list the most luminescent complexes emitting in the visible and near-IR ranges and the best chromophores are pointed out.
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Nonat, A. M.; Charbonnière, L. J. Upconversion of Light with Molecular and Supramolecular Lanthanide Complexes. Coord. Chem. Rev. 2020, 409, 213192 DOI: 10.1016/j.ccr.2020.213192
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Upconversion of light with molecular and supramolecular lanthanide complexes
Nonat, Aline M.; Charbonniere, Loic J.
Coordination Chemistry Reviews (2020), 409 (), 213192CODEN: CCHRAM; ISSN:0010-8545. (Elsevier B.V.)
A review. Upconversion (UC) is the process by which the energy of multiple photons is absorbed by a compd. and restored in the form of a photon of higher energy than the incident light, resulting in an anti-Stokes process. Although studied theor. since the middle of the last century and exptl. obsd. in the 1960's, the process was up to recently mainly restricted to solid state devices and ultimately to nanoparticles at the end of the century. At the same period, different researches were directed towards the possibility to observe UC at the mol. level and it is only recently that the phenomenon could be obsd. in discrete mol. entities in soln. with still very few examples. This review aims at explaining the difficulties encountered at the mol. level compared to the solid state and summarizes the results reported to date on UC at the mol. scale.
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Aboshyan-Sorgho, L.; Cantuel, M.; Petoud, S.; Hauser, A.; Piguet, C. Optical Sensitization and Upconversion in Discrete Polynuclear Chromium–Lanthanide Complexes. Coord. Chem. Rev. 2012, 256 (15–16), 1644– 1663, DOI: 10.1016/j.ccr.2011.12.013
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Optical sensitization and upconversion in discrete polynuclear chromium-lanthanide complexes
Aboshyan-Sorgho, Lilit; Cantuel, Martine; Petoud, Stephane; Hauser, Andreas; Piguet, Claude
Coordination Chemistry Reviews (2012), 256 (15-16), 1644-1663CODEN: CCHRAM; ISSN:0010-8545. (Elsevier B.V.)
A review. Due to its extreme kinetic inertness, trivalent chromium, Cr(III), has been rarely combined with labile trivalent lanthanides, Ln(III), to give discrete self-assembled (supra)mol. polynuclear complexes. However, the plethora of accessible metal-centered excited states possessing variable lifetimes and emissive properties, combined with the design of efficient intramol. Cr(III) ↔ Ln(III) energy transfer processes open attractive perspectives for programming directional light-conversion within these heterometallic mols. Efforts made to address this exciting challenge for both light-sensitization and light-upconversion are discussed in this article.
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Bernot, K.; Daiguebonne, C.; Calvez, G.; Suffren, Y.; Guillou, O. A Journey in Lanthanide Coordination Chemistry: From Evaporable Dimers to Magnetic Materials and Luminescent Devices. Acc. Chem. Res. 2021, 54 (2), 427– 440, DOI: 10.1021/acs.accounts.0c00684
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A Journey in Lanthanide Coordination Chemistry: From Evaporable Dimers to Magnetic Materials and Luminescent Devices
Bernot, Kevin; Daiguebonne, Carole; Calvez, Guillaume; Suffren, Yan; Guillou, Olivier
Accounts of Chemical Research (2021), 54 (2), 427-440CODEN: ACHRE4; ISSN:0001-4842. (American Chemical Society)
A review. Conspectus: Lanthanide ions are prime ingredients for the design of compds., materials, and devices with unique magnetic and optical properties. Accordingly, coordination chem. is one of the best tools for building mol. edifices from these ions because it allows careful control of the ions' environment and of the dimensionality of the final compd. In this Account, the authors review the authors' results on lanthanide-based dimers. A pure fundamental study on lanthanide coordination chem. allows the study of a full continuum of results from the compd. to materials and then to devices. The conversion of mols. into materials is a tricky task because it requires strong mol. robustness toward the surface deposition processes as well as the preservation and detectability of the mol. properties in the material. Addnl., the passage of a material toward a device implies a material with a given function, for example, a tailored response to an external stimulus. To do so, the authors targeted neutral and isolated mols. whose transfer on surfaces by chemi- or physisorption is much easier than that of charged mols. or extended coordination networks. Then, the authors focused on mols. with very strong evaporability to avoid wet chem. deposition processes that are more likely to damage the mols. and/or distort their geometries. The authors thus designed lanthanide dimers based on fluorinated β-diketonates and pyridine-N-oxide ligands. As expected, they show remarkable evaporability but also strong luminescence and interesting magnetic behavior because they behave as single-mol. magnets (SMMs). Ligand substitutions and stoichiometric modifications allow the optimization of the geometric organization of the dimers in the crystal packing as well as their evaporability, SMM behavior, luminescent properties, or their ability to be anchored on surfaces. Most of all, this family of mols. shows a strong ability to form thick films on various substrates. This allows converting these mols. to magnetic materials and luminescent devices. Magnetic materials can be designed by creating thick films of the dimers deposited on gold. These films were designed and studied with the most advanced techniques of on-surface imaging (at. force microscopy, AFM), on-surface physicochem. characterization (XPS, time of flight-secondary ion mass spectroscopy (Tof-SIMS)), and on-surface magnetic study (low-energy muon spin relaxation (LE-μSR)). Contrary to what was previously obsd. on other SMM films, no depth dependence of the SMM behavior was obsd. This means that the dimers do not suffer from the vacuum or substrate interface and behave similarly, whatever their localization. This exceptional magnetic robustness is a key ingredient in the creation of materials for mol. magnetic data storage. Luminescent devices can be obtained by layering mol. films of the dimers with a copper-rich solid-state electrolyte between ITO/Pt electrodes. The electromigration of Cu2+ ions into films of Eu3+, Tb3+, and Dy3+ dimers quenches their luminescence. This luminescence tuning by electromigration is reversible, and this setup can be considered to be a proof of concept of full solid-state luminescent device where reversible coding can be tailored by an elec. field. It is envisioned for optical data storage purposes. In the future, it could also benefit from the SMM properties of the mols. to pave the way toward multifunctional mol. data storage devices.
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Cucinotta, G.; Perfetti, M.; Luzon, J.; Etienne, M.; Car, P.-E.; Caneschi, A.; Calvez, G.; Bernot, K.; Sessoli, R. Magnetic Anisotropy in a Dysprosium/DOTA Single-Molecule Magnet: Beyond Simple Magneto-Structural Correlations. Angew. Chem., Int. Ed. 2012, 51 (7), 1606– 1610, DOI: 10.1002/anie.201107453
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Magnetic Anisotropy in a Dysprosium/DOTA Single-Molecule Magnet: Beyond Simple Magneto-Structural Correlations
Cucinotta, Giuseppe; Perfetti, Mauro; Luzon, Javier; Etienne, Mael; Car, Pierre-Emmanuel; Caneschi, Andrea; Calvez, Guillaume; Bernot, Kevin; Sessoli, Roberta
Angewandte Chemie, International Edition (2012), 51 (7), 1606-1610, S1606/1-S1606/11CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
Single-crystal magnetic investigations have been shown to be required to study mol. systems that are based on anisotropic lanthanide ions. The detailed exptl. and theor. investigation on one of the most studied lanthanide coordination compds. has provided several key results. The most important one is that simple magnetostructural correlations based on the coordination environment can fail to predict, even approx., the correct magnetic anisotropy of anisotropic lanthanide ions in a low-symmetry environment. Subtle structural details, like the position of hydrogen atoms and the consequent orientation of the nonbonding orbitals of the axial ligand can overcome the symmetry imposed by the coordination polyhedron. The well-resolved luminescence spectra, which allow the energy splitting of the 6H15n multiplet to be detd., have provided precious indications, which confirm that the first excited doublet plays a key role in the magnetization dynamics. .Finally, post Hartree-Fock ab initio calcns. were confirmed to be an invaluable method for the prediction and rationalization of the magnetic anisotropy, provided that subtle structural details are also correctly taken into account. The evaluation of the energy splitting seems, however, even more critically dependent on which structural model and basis sets are used. In modeling the relaxivity effects it is generally assumed that the orientation of the M-Owater of DOTA-like complexes corresponds to the anisotropy axis and that the apical water mols. lie in the cone of highest susceptibility. The authors have shown here that this is probably not the case and we also suspect that the mechanism of contrast in the nuclear relaxation is more complex because the labile water mol. modifies the magnetic anisotropy of the lanthanide ion.
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Shannon, R. D. Revised Effective Ionic Radii and Systematic Studies of Interatomic Distances in Halides and Chaleogenides. Acta Crystallogr., A 1976, 32, 751– 767, DOI: 10.1107/S0567739476001551
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Baloch, A. A. B.; Alqahtani, S. M.; Mumtaz, F.; Muqaibel, A. H.; Rashkeev, S. N.; Alharbi, F. H. Extending Shannon’s Ionic Radii Database Using Machine Learning. Phys. Rev. Mater. 2021, 5 (4), 043804 DOI: 10.1103/PhysRevMaterials.5.043804
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Extending Shannon's ionic radii database using machine learning
Baloch, Ahmer A. B.; Alqahtani, Saad M.; Mumtaz, Faisal; Muqaibel, Ali H.; Rashkeev, Sergey N.; Alharbi, Fahhad H.
Physical Review Materials (2021), 5 (4), 043804CODEN: PRMHBS; ISSN:2475-9953. (American Physical Society)
In computational material design, ionic radius is one of the most important phys. parameters used to predict material properties. Motivated by the progress in computational materials science and material informatics, we extend the renowned Shannon's table from 475 ions to 987 ions. Accordingly, a rigorous machine learning (ML) approach is employed to extend the ionic radii table using all possible combinations of oxidn. states (OS) and coordination nos. (CN) available in crystallog. repositories. An ionic-radius regression model for Shannon's database is developed as a function of the period no., the valence orbital configuration, OS, CN, and ionization potential. In the Gaussian process regression (GPR) model, the reached R2 accuracy is 99while the root mean square error of radii is 0.0332 Å. The optimized GPR model is then employed for predicting a new set of ionic radii for uncommon combinations of OS and CN extd. by harnessing crystal structures from materials project databases. The generated data are consolidated with the reputable Shannon's data and are made available online in a database repository.
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Lundberg, D.; Persson, I.; Eriksson, L.; D’Angelo, P.; De Panfilis, S. Structural Study of the N,N′ -Dimethylpropyleneurea Solvated Lanthanoid(III) Ions in Solution and Solid State with an Analysis of the Ionic Radii of Lanthanoid(III) Ions. Inorg. Chem. 2010, 49 (10), 4420– 4432, DOI: 10.1021/ic100034q
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Structural Study of the N,N'-Dimethylpropyleneurea Solvated Lanthanoid(III) Ions in Solution and Solid State with an Analysis of the Ionic Radii of Lanthanoid(III) Ions
Lundberg, Daniel; Persson, Ingmar; Eriksson, Lars; D'Angelo, Paola; De Panfilis, Simone
Inorganic Chemistry (2010), 49 (10), 4420-4432CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
The structures of the N,N'-dimethylpropyleneurea (dmpu) solvated lanthanoid(III) ions have been studied in dmpu soln. (La-Nd, Sm-Lu) and in solid iodide salts (La-Nd, Sm, Gd-Lu) by extended X-ray absorption fine structure (EXAFS), and single crystal X-ray diffraction (La, Pr, Nd, Gd, Tb, Er, Yb, and Lu); the EXAFS studies were performed on both K and LIII absorption edges. Because of the space-demanding properties of dmpu upon coordination, dmpu solvated metal ions often show coordination nos. lower than those found in corresponding hydrates and solvates of oxygen donor solvents without steric requirements beyond the size of the donor atom. All lanthanoid(III) ions are seven-coordinate in soln., except lutetium(III) which is six-coordinated in regular octahedral fashion, whereas in the solid iodide salts the dmpu solvated lanthanoid(III) ions are all six-coordinate in regular octahedral fashion. A comparison of Ln-O bond lengths in a large no. of lanthanoid(III) complexes with neutral oxygen donor ligands and different configurations shows that the metal ion-oxygen distance is specific for each coordination no. with a narrow bond distance distribution. This also shows that the radius of the coordinated oxygen atom in these compds. can be assumed to be 1.34 Å as proposed for coordinated water, while for ethers such as THF it is somewhat larger. Using this at. radius of oxygen in coordinated water mols., we have calcd. the ionic radii of the lanthanoid(III) ions in four- to nine-coordination and evaluated using the bond lengths reported for homo- and heteroleptic complexes in oxygen donor solvates in soln. and solid state. This yields new and revised ionic radii which in some instances are significantly different from the ionic radii normally referenced in the literature, including interpolated values for the elusive promethium(III) ion.
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Seitz, M.; Oliver, A. G.; Raymond, K. N. The Lanthanide Contraction Revisited. J. Am. Chem. Soc. 2007, 129 (36), 11153– 11160, DOI: 10.1021/ja072750f
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The Lanthanide Contraction Revisited
Seitz, Michael; Oliver, Allen G.; Raymond, Kenneth N.
Journal of the American Chemical Society (2007), 129 (36), 11153-11160CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
A complete, isostructural series of complexes with La-Lu (except Pm) with the ligand TREN-1,2-HOIQO (I), [M(TREN-1,2-HOIQO-3H)(H2O)]·H2O, was synthesized and structurally characterized by single-crystal x-ray anal. All complexes are 1-dimensional polymeric species in the solid state, with the lanthanide being in an eight-coordinate, distorted trigonal-dodecahedral environment with a donor set of eight unique oxygen atoms. This series constitutes the 1st complete set of isostructural complexes from La-Lu (without Pm) with a ligand of denticity greater than two. The geometric arrangement of the chelating moieties slightly deviates across the lanthanide series, as analyzed by a shape parameter metric based on the comparison of the dihedral angles along all edges of the coordination polyhedron. The apparent lanthanide contraction in the individual Ln-O bond lengths deviates considerably from the expected quadratic decrease that was found previously in a no. of complexes with ligands of low denticity. The sum of all bond lengths around the trivalent metal cation, however, is more regular, showing an almost ideal quadratic behavior across the entire series. The quadratic nature of the lanthanide contraction is derived theor. from Slater's model for the calcn. of ionic radii. The sum of all distances along the edges of the coordination polyhedron show exactly the same quadratic dependence as the Ln-X bond lengths. The universal validity of this coordination sphere contraction, concomitant with the quadratic decrease in Ln-X bond lengths, was confirmed by reexamn. of four other, previously published series of lanthanide complexes. Owing to the importance of multidentate ligands for the chelation of rare-earth metals, this result provides a significant advance for the prediction and rationalization of the geometric features of the corresponding lanthanide complexes, with great potential impact for all aspects of lanthanide coordination.
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Peters, J. A.; Djanashvili, K.; Geraldes, C. F. G. C.; Platas-Iglesias, C. The Chemical Consequences of the Gradual Decrease of the Ionic Radius along the Ln-Series. Coord. Chem. Rev. 2020, 406, 213146 DOI: 10.1016/j.ccr.2019.213146
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The chemical consequences of the gradual decrease of the ionic radius along the Ln-series
Peters, Joop A.; Djanashvili, Kristina; Geraldes, Carlos F. G. C.; Platas-Iglesias, Carlos
Coordination Chemistry Reviews (2020), 406 (), 213146CODEN: CCHRAM; ISSN:0010-8545. (Elsevier B.V.)
In the periodical system, the lanthanides (the 15 elements in the periodic table between barium and hafnium) are unique in the sense that their trivalent cations have their valence electrons hidden behind the 5s and 5p electrons. They show a gradual decrease in ionic radius with increasing at. no. (also known as the lanthanide contraction). The resulting steric effects det. to a large extent the geometries of complexes of these ions. Here, we discuss these effects, particularly upon the properties of the complexes in aq. soln., for selected families of Ln3+-complexes of oxycarboxylate and aminocarboxylate ligands. The phys. properties of the cations are very different, which is very useful for the elucidation of the configuration, conformation and the dynamics of the complexes by X-ray techniques, NMR spectroscopy, and optical techniques. Often the structural anal. is assisted by computational methods.
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Jordan, R. B. Lanthanide Contraction: What Is Normal?. Inorg. Chem. 2023, 62, 3715– 3721, DOI: 10.1021/acs.inorgchem.2c03674
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Lanthanide Contraction: What is Normal?
Jordan, Robert B.
Inorganic Chemistry (2023), 62 (9), 3715-3721CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
Renewed interest in lanthanide contraction results from its possible effect on the properties and applications of Ln(III) compds. and the theory related to these issues. To understand this effect, it is important to know what is a normal dependence of the contraction on the no. of 4f electrons, n. The normal trend is based on recent values of ionic radii that have a linear dependence on n for coordination nos. (CNs) of 6, 8, and 9. If the normal trend is not followed, then some other interactions in the system are affecting the extent of contraction. However, the suggestion that the variation is curved and fitted by a quadratic function has become popular in recent years. This report examines the Ln(III)-to-ligand atom distances for coordination compds. with CNs of 6-9 and the nitrides and phosphides. Least-squares fits to the linear and quadratic models are applied to all of the bond distances to det. when a quadratic model is justified. The result is that complex systems show a mixt. of linear and quadratic dependencies when individual bond distances are considered and that the linear model is most common and representative of the true lanthanide contraction.
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Bart, S. C. What Is the “Lanthanide Contraction”?. Inorg. Chem. 2023, 62, 3713– 3714, DOI: 10.1021/acs.inorgchem.3c00440
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What is the "Lanthanide Contraction"?
Bart, Suzanne C.
Inorganic Chemistry (2023), 62 (9), 3713-3714CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
There is no expanded citation for this reference.
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Fyfe, W. S. The Problem of Bond Type. Am. Mineral. 1954, 39, 991– 1004
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The problem of bond type
Fyfe, W. S.
American Mineralogist (1954), 39 (), 991-1004CODEN: AMMIAY; ISSN:0003-004X.
cf. C.A. 47, 11868g. Consideration of electronegativities is inadequate for quant. evaluation of the proportions of ionic and covalent bonding in a compd. The overlap integrals give better values, as illustrated for the alkali halides, and by comparison of Si-O and C-O bonds.
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Kawabe, I. Lanthanide Tetrad Effect in the Ln³⁺ Ionic Radii and Refined Spin-Pairing Energy Theory. Geochem. J. 1992, 26 (6), 309– 335, DOI: 10.2343/geochemj.26.309
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Lanthanide tetrad effect in the Ln3+ ionic radii and refined spin-pairing energy theory
Kawabe, Iwao
Geochemical Journal (1992), 26 (6), 309-35CODEN: GEJOBE; ISSN:0016-7002.
The refined spin-pairing energy theory (RSPET) has been improved in order to understand quant. the tetrad or double-double effects recognized in the Ln3+ ionic radii. Since the ionic radii have been detd. from the lattice consts. and structural parameters of LnO1.5 and LnF3, the lattice energies of the compds. and the enthalpy difference of ΔHf°(LnF3) - ΔHf°(LnO1.5) have been examd. by the improved RSPET. The RSPET parameters for the lowest levels of 4fq electronic configurations strongly depend upon the effective nuclear charge (Z*). Such effects due to Z* have been taken into account. This made it possible to sep. the variations in the lattice energies and the enthalpy difference across the Ln3+ series into the following two parts: (1) the large variation as a smooth function of q (the lanthanide contraction trend), and (2) the small zig-zag variation referred to the tetrad or double-double effect. The lattice energy of LnO1.5 and ΔHf°(LnF3) - ΔHf°(LnO1.5) exhibit upward concave tetrad curves in their plots against q of Ln3+. The tetrad effect in the lattice energy of LnF3 is less conspicuous. This means that the Racah parameters for Ln3+ decrease very slightly in going from the gaseous free Ln3+ to LnF3, and then decrease greatly to LnO1.5, in accordance with the nephelauxetic series. The differences in Racah parameters between LnF3 and LnO1.5 have been estd. from ΔHf°(LnF3) - ΔHf°(LnO1.5) by means of an inversion technique based on the improved RSPET. The RSPET results for the thermochem. data are consistent with the careful spectroscopic detns. of Racah parameters for NdF3 and NdO1.5. Both the tetrad effect and the smooth lanthanide contraction seen in the Ln3+ ionic radii can be interpreted in terms of the quantum mech. energetics of 4f electrons.
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Gibbs, G. V.; Tamada, O.; Boisen, M. B., Jr. Atomic and Ionic Radii: A Comparison with Radii Derived from Electron Density Distributions. Phys. Chem. Miner. 1997, 24 (6), 432– 439, DOI: 10.1007/s002690050057
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Atomic and ionic radii: a comparison with radii derived from electron density distributions
Gibbs, G. V.; Tamada, Osamu; Boisen, M. B., Jr.
Physics and Chemistry of Minerals (1997), 24 (6), 432-439CODEN: PCMIDU; ISSN:0342-1791. (Springer)
The bonded radii of anions obtained in topol. analyses of theor. and exptl. electron d. distributions differ from at., ionic and crystal radii in that oxide-, fluoride-, nitride- and sulfide-anion radii are not const. for a given coordination no. They vary in a regular way with bond length and the electronegativity of the cation to which they are bonded, exhibiting radii close to at. radii when bonded to a highly electroneg. cation and radii close to ionic radii when bonded to a highly electropos. cation. The electron d. distributions show that anions are not spherical but exhibit several different radii in different bonded directions. The bonded radii of cations correlate with ionic and at. radii. But unlike ionic radii, the bonded radius of a cation shows a relatively small increase in value with an increase in coordination no. In contrast to at. and ionic radii, the bonded radius of an ion in a crystal or mol. can be used as a reliable and well-defined est. of its radius in the direction of its bonds.
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Gibbs, G. V.; Ross, N. L.; Cox, D. F.; Rosso, K. M.; Iversen, B. B.; Spackman, M. A. Bonded Radii and the Contraction of the Electron Density of the Oxygen Atom by Bonded Interactions. J. Phys. Chem. A 2013, 117 (7), 1632– 1640, DOI: 10.1021/jp310462g
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Bonded Radii and the Contraction of the Electron Density of the Oxygen Atom by Bonded Interactions
Gibbs, Gerald V.; Ross, Nancy L.; Cox, David F.; Rosso, Kevin M.; Iversen, Bo B.; Spackman, Mark A.
Journal of Physical Chemistry A (2013), 117 (7), 1632-1640CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)
The bonded radii for more than 700 bonded pairs of atoms, comprising more than 50 oxide crystals, extd. from exptl. and theor. electron d. distributions, are averaged and compared with the ionic radii for first, second, and third row atoms. At odds with the assumption of a fixed ionic radius of 1.40 Å for the oxide anion, the bonded radius for the anion, rb(O), decreases systematically from 1.40 to 0.65 Å as the electron d. distribution of the atom is progressively polarized and contracted by its bonded interactions. The radii for the more electropos. metal atoms agree with the ionic radii when the electron d. distribution of the anion is largely unpolarized by its bonded interactions. However, those for the more electroneg. metal atoms are progressively larger than the ionic radii as the electron d. distribution of the anion is progressively polarized and contracted along the bond vectors with decreasing bond length. The progressive decrease of rb(O) indicates that the compilation of sets of ionic radii, based on a fixed radius for the oxide anion, is problematic and impacts the accuracy of the ionic radii for the metal atoms. The assumption of a fixed radius for the anion, made in the derivation of sets of radii, not only results in unrealistic neg. ionic radii for the more electroneg. atoms but also in ionic radii that are as much as 0.5 Å smaller than the bonded radii, particularly for the more electroneg. M atoms. The lack of agreement between the ionic and the bonded radii for the more shared bonded interactions is ascribed to the progressive increase in the polarization and contraction of the electron d. of the oxide anion by the bonded interactions with a concomitant decrease in the radius of the anion, a factor that was largely neglected in the compilation of the ionic radii for fluoride, oxide, sulfide, and nitride crystals. The close agreement of the bonded radii and procrystal bonded radii is consistent with the argument that the chem. forces that govern the electron d. distributions and bonded radii are largely at. in nature, resulting in comparable electron d. distributions.
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Rahm, M.; Hoffmann, R.; Ashcroft, N. W. Atomic and Ionic Radii of Elements 1–96. Chem. – Eur. J. 2016, 22 (41), 14625– 14632, DOI: 10.1002/chem.201602949
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Atomic and Ionic Radii of Elements 1-96
Rahm, Martin; Hoffmann, Roald; Ashcroft, N. W.
Chemistry - A European Journal (2016), 22 (41), 14625-14632CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)
Atomic and cationic radii have been calcd. for the first 96 elements, together with selected anionic radii. The metric adopted is the av. distance from the nucleus where the electron d. falls to 0.001 electrons per bohr3, following earlier work by Boyd. Our radii are derived using relativistic all-electron d. functional theory calcns., close to the basis set limit. They offer a systematic quant. measure of the sizes of non-interacting atoms, commonly invoked in the rationalization of chem. bonding, structure, and different properties. Remarkably, the at. radii as defined in this way correlate well with van der Waals radii derived from crystal structures. A rationalization for trends and exceptions in those correlations is provided.
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Liu, J.-B.; Schwarz, W. H. E.; Li, J. On Two Different Objectives of the Concepts of Ionic Radii. Chem. – Eur. J. 2013, 19 (44), 14758– 14767, DOI: 10.1002/chem.201300917
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On Two Different Objectives of the Concepts of Ionic Radii
Liu, Jian-Biao; Schwarz, W. H. Eugen; Li, Jun
Chemistry - A European Journal (2013), 19 (44), 14758-14767CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)
Exptl. and theor. derived interat. distances (D) and ionic radii (R) of more than a hundred monomeric (AX), dimeric (A2X2, ABXY), and cryst. ([AX]) alkali halide species (A=Li, Na, K, Rb, Cs, Fr; X=H, F, Cl, Br, I, At) have been analyzed. Chemists use the word "at. radius" for two antithetic concepts. Let DCiEE'jj' be the "billion" of distances i between two adjacent atoms in the millions of known compds. C from a hundred different elements E in bonding states j. The common chem. aim is partitioning D approx. into increments REj + RE'j'. This can be achieved with a few (say <thousand) predictive consts. REj. An antipodal aim is specifying in hindsight an electron d. feature in the "billion" of different bonds i, by partitioning them into "two billions" of exact bonded radii RECi + RE'Ci. The const. incremental and the variable bonded radii concepts with the same generic name are useful in different fields of research. Different concepts should be well distinguished, since they have different meaning, different numerical values, and different purposes.
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Cordero, B.; Gómez, V.; Platero-Prats, A. E.; Revés, M.; Echeverría, J.; Cremades, E.; Barragán, F.; Alvarez, S. Covalent Radii Revisited. Dalton Trans. 2008, 21, 2832– 2838, DOI: 10.1039/b801115j
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Pyykkö, P.; Atsumi, M. Molecular Single-Bond Covalent Radii for Elements 1–118. Chem. – Eur. J. 2009, 15 (1), 186– 197, DOI: 10.1002/chem.200800987
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Pyykkö, P. Additive Covalent Radii for Single-, Double-, and Triple-Bonded Molecules and Tetrahedrally Bonded Crystals: A Summary. J. Phys. Chem. A 2015, 119 (11), 2326– 2337, DOI: 10.1021/jp5065819
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Additive Covalent Radii for Single-, Double-, and Triple-Bonded Molecules and Tetrahedrally Bonded Crystals: A Summary
Pyykko, Pekka
Journal of Physical Chemistry A (2015), 119 (11), 2326-2337CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)
A review. The recent fits of additive covalent radii RAB = rA + rB for the title systems are reviewed and compared with alternative systems of radii by other authors or with further exptl. data. The agreement of the predicted R with expt. is good, provided that the A-B bond is not too ionic, or the coordination nos. of the two atoms too different from the original input data, used in the fit. Bonds between transition metals and halides are not included in the single-bond set, because of their partial multiple-bond character.
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Gunnlaugsson, T.; Leonard, J. P.; Mulready, S.; Nieuwenhuyzen, M. Three Step vs One Pot Synthesis and X-Ray Crystallographic Investigation of Heptadentate Triamide Cyclen (1,4,7,10-Tetraazacyclododecane) Based Ligands and Some of Their Lanthanide Ion Complexes. Tetrahedron 2004, 60 (1), 105– 113, DOI: 10.1016/j.tet.2003.10.086
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Three step vs. one pot synthesis and X-ray crystallographic investigation of heptadentate triamide cyclen (1,4,7,10-tetraazacyclododecane) based ligands and some of their lanthanide ion complexes
Gunnlaugsson, Thorfinnur; Leonard, Joseph P.; Mulready, Sinead; Nieuwenhuyzen, Mark
Tetrahedron (2004), 60 (1), 105-113CODEN: TETRAB; ISSN:0040-4020. (Elsevier Science B.V.)
The synthesis of several lanthanide complexes from the tris alkylated cyclen (1,4,7,10-tetraazacyclododecane) ligands (I, R = Me, 1;R = H, 2) is described. The prepn. of 1 and 2 were studied by two different synthetic routes (Methods 1 and 2). The 1st of these involves the mono protection of cyclen using 4-methoxyphenylsulfonyl chloride, followed by alkylation of the remaining three secondary amines of cyclen, and deprotection using solvated Na(s). Using this approach only 1 was successfully formed. The x-ray crystal structure of the intermediate, (II = 9) and the corresponding La(III) complex, 9·La is presented. The 2nd method involved the direct synthesis of the two ligands in a single step. The x-ray crystallog. of the Eu(III) complex of one of these ligands is presented. Whereas, Method 1 yielded the product 1 in high purity, but in low overall yield, Method 2 gave higher yields for both ligands (∼50% for both).
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Amin, S.; Morrow, J. R.; Lake, C. H.; Churchill, M. R. Lanthanide(III) Tetraamide Macrocyclic Complexes as Synthetic Ribonucleases: Structure and Catalytic Properties of[La(Tcmc)(CF3SO3)(EtOH)](CF3SO3)2. Angew. Chem., Int. Ed. 1994, 33 (7), 773– 775, DOI: 10.1002/anie.199407731
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Franklin, S. J.; Raymond, K. N. Solution Structure and Dynamics of Lanthanide Complexes of the Macrocyclic Polyamino Carboxylate DTPA-Dien. NMR Study and Crystal Structures of the Lanthanum(III) and Europium(III) Complexes. Inorg. Chem. 1994, 33 (25), 5794– 5804, DOI: 10.1021/ic00103a029
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Solution Structure and Dynamics of Lanthanide Complexes of the Macrocyclic Polyamino Carboxylate DTPA-dien. NMR Study and Crystal Structures of the Lanthanum(III) and Europium(III) Complexes
Franklin, Sonya J.; Raymond, Kenneth N.
Inorganic Chemistry (1994), 33 (25), 5794-804CODEN: INOCAJ; ISSN:0020-1669.
An 18-membered macrocyclic DTPA-bis(amide) ligand (I; DTPA = diethylenetriaminepentaacetic acid) contg. a heteroatom in the amide link was prepd. via the condensation of DTPA-dianhydride and diethylenetriamine. The soln. structures of the two isomeric pairs present in the Ln(III) complexes of DTPA-dien were studied by 1H NMR. One enantiomeric pair exhibits slow exchange on the NMR time scale at low temps. (0-25°) and dynamic behavior at higher temps. The other isomeric pair exhibits an unusual static behavior; exchange remains slow even at 95°. Peak assignments for the Eu(DTPA-dien) spectra are given based on deuteration studies, 2-dimensional COSY spectroscopy, and 2-dimensional EXSY spectroscopy. 2D EXSY spectroscopy at several temps. and mixing times showed that ΔG⧧299 for the dynamic isomerization is 57.5 ± 0.3 kJ/mol, and that the dynamic isomer is an intermediate for the static isomerization, which occurs with a change in backbone amine chirality. The structures of the La(III) and Eu(III) DTPA-dien complexes were detd. by x-ray anal. [La(DTPA-dienH+)H2O]2(CF3SO3-)2·18H2O crystallizes as a carboxylate-bridged dimer about a center of inversion in the orthorhombic space group Pbca with a 12.626(2), b 21.405(3), c 26.422(9) Å, and Z = 8. Each La ion is 11-coordinate with octadentate ligand coordination, an η2 bridging carboxylate, and one H2O. [Eu(DTPA-dienH+)]4(CF3SO3-)4·6NaCF3SO3·20H2O crystallizes as a carboxylate-bridged tetramer with two crystallog. independent Eu(III) positions (Z = 8 for each) in the monoclinic space group C2/c: a 30.94(1), b 23.456(3), c 22.611(4) Å, β 105.78(2)°. The coordination geometries about Eu1 and Eu2 are nearly identical and are described as a nine-coordinate tricapped trigonal prism with octadentate ligand coordination plus an η1 bridging carboxylate. The tendency to oligomerize is attributed to the constraints imposed by the macrocycle and the H bonding available with the link heteroatom. The structural differences between the two complexes are attributed to a difference in La(III) and Eu(III) ionic size. The soln. structure of the dynamic isomer is the same as the monomer unit of the crystal structures, and the static isomer is similar, save for a change in one terminal backbone nitrogens' chirality.
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Nakai, H.; Nonaka, K.; Goto, T.; Seo, J.; Matsumoto, T.; Ogo, S. A Macrocyclic Tetraamine Bearing Four Phenol Groups: A New Class of Heptadentate Ligands to Provide an Oxygen-Sensitive Luminescent Tb(iii) Complex with an Extendable Phenol Pendant Arm. Dalton Trans. 2015, 44 (24), 10923– 10927, DOI: 10.1039/C5DT00816F
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A macrocyclic tetraamine bearing four phenol groups: a new class of heptadentate ligands to provide an oxygen-sensitive luminescent Tb(III) complex with an extendable phenol pendant arm
Nakai, Hidetaka; Nonaka, Kyoshiro; Goto, Takahiro; Seo, Juncheol; Matsumoto, Takahiro; Ogo, Seiji
Dalton Transactions (2015), 44 (24), 10923-10927CODEN: DTARAF; ISSN:1477-9226. (Royal Society of Chemistry)
This paper presents a 1,4,7,10-teraazacyclododecane-based tetrakis-phenol (H4L) as a protonated ligand precursor and its oxygen-sensitive luminescent terbium(III) complex with an extendable phenol pendant arm (Φ = 0.91 under N2, Φ = 0.031 under air), in which the potentially N4O4-octadentate ligand unprecedentedly coordinates to the Tb3+ ion in a N4O3-heptadentate fashion (1, TbL).
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Wen, H.-R.; Zhang, J.-L.; Liang, F.-Y.; Yang, K.; Liu, S.-J.; Liu, C.-M. Multifunctional Lanthanide Complexes Based on Tetraazacyclolamidophenol Ligand with Field-Induced Slow Magnetic Relaxation, Luminescent and SHG Properties: Multifunctional Lanthanide Complexes Based on Tetraazacyclolamidophenol Ligand with Field-Induced Slow Magnetic Relaxation, Luminescent and SHG Proper. Eur. J. Inorg. Chem. 2019, 2019 (10), 1406– 1412, DOI: 10.1002/ejic.201801492
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Multifunctional Lanthanide Complexes Based on Tetraazacyclolamidophenol Ligand with Field-Induced Slow Magnetic Relaxation, Luminescent and SHG Properties
Wen, He-Rui; Zhang, Jia-Li; Liang, Fu-Yong; Yang, Kai; Liu, Sui-Jun; Liu, Cai-Ming
European Journal of Inorganic Chemistry (2019), 2019 (10), 1406-1412CODEN: EJICFO; ISSN:1434-1948. (Wiley-VCH Verlag GmbH & Co. KGaA)
Two multifunctional lanthanide complexes, [Dy(HL)]·MeOH (1) and [Er(HL)]·MeOH (2), [H4L = N,N',N'',N'''-tetra(3,5-dimethyl-2-Hydroxybenzyl)-1,4,7,10-tetraazacyclododecane] were synthesized and structurally characterized. Complexes 1 and 2 are isomorphic and crystallize in the noncentrosym. orthorhombic space group Pca21. Their structure consists of one seven-coordinated LnIII ion with the coordination geometry of trigonal prism, one HL3- ligand and one lattice MeOH mol. They exhibit 2nd-harmonic generation (SHG) effect. Complex 1 displays strong fluorescent emissions, which are typical narrow emission bands of lanthanide ions. Complex 1 features field-induced slow magnetic relaxation behavior. Therefore, complex 1 may be a potential multifunctional mol. material.
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Urbanovský, P.; Kotek, J.; Císařová, I.; Hermann, P. The Solid-State Structures and Ligand Cavity Evaluation of Lanthanide(III) Complexes of a DOTA Analogue with a (Dibenzylamino)Methylphosphinate Pendant Arm. Dalton Trans. 2020, 49 (5), 1555– 1569, DOI: 10.1039/C9DT04056K
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The solid-state structures and ligand cavity evaluation of lanthanide(III) complexes of a DOTA analogue with a (dibenzylamino)methylphosphinate pendant arm
Urbanovsky, Peter; Kotek, Jan; Cisarova, Ivana; Hermann, Petr
Dalton Transactions (2020), 49 (5), 1555-1569CODEN: DTARAF; ISSN:1477-9226. (Royal Society of Chemistry)
A series of lanthanide(III) complexes of a monophosphinate analog of H4dota, 1,4,7,10-tetraazacyclododecane-1,4,7-triacetic-10-methyl[(N,N-dibenzylamino)methyl]phosphinic acid (H4do3apDBAm = H4L1), were prepd. and their solid-state structures were studied using single-crystal X-ray diffraction. In all structures, the ligand anion was octadentately coordinated to the Ln(III) or Sc(III) ions similarly to other DOTA-like ligands, i.e. forming parallel N4- and O4-planes. The lighter lanthanide(III) complexes (till dysprosium) were nonacoordinated in the twisted square-antiprismatic (TSA) configuration with the apical coordination of water mols. or oxygen atoms from the neighboring complex unit. The heavier lanthanide(III) complexes (from terbium) were found as the "anhyd." octacoordinated twisted square-antiprismatic (TSA') isomer. For the terbium(III) ion, both forms were structurally characterized. The structural data of the Ln(III)-H4L1 complexes and complexes of several related DOTA-like ligands were analyzed. It clearly showed that the structural parameters for the square-antiprismatic (SA) isomers were clustered in a small range while those for the TSA/TSA' isomers were significantly more spread. The anal. also gave useful information about the influence of various pendant arms on the structure of the complexes of the DOTA-like ligands. The twist angle (torsion) of the chelate ring contg. a larger phosphorus atom was similar to those of the remaining three acetate pendants. It led to a larger sepn. of the N4···O4 planes and to smaller trans-O-Ln-O angles than the parameters found in the complexes of H4dota and its tetraamide derivs. dotam(R). It resulted in a relatively long bond between the metal ion and the coordinated water mol. It led, together with the neg. charge of the oxygen atoms forming the O4-plane, to an extremely fast water exchange rate reported for the Gd(III)-H4L1 complex and, generally, to a fast water exchange of Gd(III) complexes with the monophosphorus acid analogs of H4dota, H5do3ap/H4do3apR.
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Woods, M.; Payne, K. M.; Valente, E. J.; Kucera, B. E.; Young, V. G. Crystal Structures of DOTMA Chelates from Ce³⁺ to Yb³⁺: Evidence for a Continuum of Metal Ion Hydration States. Chem. – Eur. J. 2019, 25 (42), 9997– 10005, DOI: 10.1002/chem.201902068
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Crystal Structures of DOTMA Chelates from Ce3+ to Yb3+: Evidence for a Continuum of Metal Ion Hydration States
Woods, Mark; Payne, Katherine M.; Valente, Edward J.; Kucera, Benjamin E.; Young, Victor G. Jr.
Chemistry - A European Journal (2019), 25 (42), 9997-10005CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)
The crystal structures of chelates formed between each stable paramagnetic lanthanide ion and the octadentate polyamino carboxylate ligand DOTMA are described. A total of 23 individual chelates structures were obtained; in each chelate the coordination geometry around the metal ion is best described as a twisted square antiprism (torsion angle -25.0°--31.4°). Despite the uniformity of the general coordination geometry provided by the DOTMA ligand, there is a considerable variation in the hydration state of each chelate. The early Ln3+ chelates are assocd. with a single inner sphere water mol.; the Ln-OH2 interaction is remarkable for being very long. After a clear break at gadolinium, the no. of chelates in the unit cell that have a water mol. interacting with the Ln3+ decreases linearly until at Tm3+ no water is found to interact with the metal ion. The Ln-OH2 distance obsd. in the chelates of the later Ln3+ ions are also extremely long and increase as the ions contract (2.550-2.732 Å). No clear break between hydrated and dehydrated chelates is obsd.; rather this series of chelates appear to represent a continuum of hydration states in which the ligand gradually closes around the metal ion as its ionic radius decreases (with decreased hydration) and the metal drops down into the coordination cage.
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Starynowicz, P. Complexes of Divalent Europium with Dotp and Dotpph. New J. Chem. 2021, 45 (13), 5879– 5889, DOI: 10.1039/D1NJ00393C
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Complexes of divalent europium with dotp and dotpph
Starynowicz, Przemyslaw
New Journal of Chemistry (2021), 45 (13), 5879-5889CODEN: NJCHE5; ISSN:1144-0546. (Royal Society of Chemistry)
Two complexes of divalent europium, with 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrakis(methylene phosphonate) (dotp) and 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrakis(methylene P-phenylphosphinate) (dotpph), were obtained by electrochem. synthesis. In both compds., the Eu2+ cation is 8-coordinate, surrounded by 4 oxygen atoms from phosphonate or phosphinate groups and 4 nitrogen atoms. The complex with dotp shows green luminescence at 77 K, while in the dotpph complex the emission is almost completely quenched. The TD DFT calcns. suggest that in both complexes the emission is of anomalous character: s → f for the first complex and π* → f for the other. Polarog. half-wave potentials of both complexes are similar to those of Eu aminopolycarboxylates. The Eu-O bonds, analyzed using topol. methods, are ionic; the Eu-N bonds in the first complex show a certain degree of covalency, while in the other one they are ionic.
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Basal, L. A.; Bailey, M. D.; Romero, J.; Ali, M. M.; Kurenbekova, L.; Yustein, J.; Pautler, R. G.; Allen, M. J. Fluorinated Eu^II -Based Multimodal Contrast Agent for Temperature- and Redox-Responsive Magnetic Resonance Imaging. Chem. Sci. 2017, 8 (12), 8345– 8350, DOI: 10.1039/C7SC03142D
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Fluorinated EuII-based multimodal contrast agent for temperature- and redox-responsive magnetic resonance imaging
Basal, Lina A.; Bailey, Matthew D.; Romero, Jonathan; Ali, Meser M.; Kurenbekova, Lyazat; Yustein, Jason; Pautler, Robia G.; Allen, Matthew J.
Chemical Science (2017), 8 (12), 8345-8350CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)
Magnetic resonance imaging (MRI) using redox-active, EuII-contg. complexes is one of the most promising techniques for noninvasively imaging hypoxia in vivo. In this technique, pos. (T1-weighted) contrast enhancement persists in areas of relatively low oxidizing ability, such as hypoxic tissue. Herein, we describe a fluorinated, EuII-contg. complex in which the redox-active metal is caged by intramol. interactions. The position of the fluorine atoms enables temp.-responsive contrast enhancement in the reduced form of the contrast agent and detection of the oxidized contrast agent via MRI in vivo. Pos. contrast is obsd. in 1H-MRI with Eu in the +2 oxidn. state, and chem. exchange satn. transfer and 19F-MRI signal are obsd. with Eu in the +3 oxidn. state. Contrast enhancement is controlled by the redox state of Eu, and modulated by the fluorous interactions that cage a bound water mol. reduce relaxivity in a temp.-dependent fashion. Together, these advancements constitute the first report of in vivo, redox-responsive imaging using 19F-MRI.
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Burai, L.; Tóth, É.; Seibig, S.; Scopelliti, R.; Merbach, A. E. Solution and Solid-State Characterization of EuII Chelates: A Possible Route Towards Redox Responsive MRI Contrast Agents. Chem. – Eur. J. 2000, 6 (20), 3761– 3770, DOI: 10.1002/1521-3765(20001016)6:20<3761::AID-CHEM3761>3.0.CO;2-6
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Solution and solid-state characterization of EuII chelates: a possible route towards redox responsive MRI contrast agents
Burai, Laszlo; Toth, Eva; Seibig, Sabine; Scopelliti, Rosario; Merbach, Andre E.
Chemistry - A European Journal (2000), 6 (20), 3761-3770CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH)
We report the first solid state X-ray crystal structure for a EuII chelate, [C(NH2)3]3[EuII(DTPA)(H2O)]·8H2O, in comparison with those for the corresponding Sr analog, [C(NH2)3]3[Sr(DTPA)(H2O)]·8H2O and for [Sr(ODDA)]·8H2O (DTPA5- = diethylenetriamine-N,N,N',N",N"-pentaacetate, ODDA2- = 1,4,10,13-tetraoxa-7,16-diaza-cyclooctadecane-7,16-diacetate). The two DTPA complexes are isostructural due to the similar ionic size and charge of Sr2+ and Eu2+. The redox stability of [EuII(ODDA)(H2O)] and [EuII(ODDM)]2- complexes has been investigated by cyclovoltammetry and UV/Vis spectrophotometry (ODDM4- = 1,4,10,13-tetraoxa-7,16-diaza-cyclooctadecane-7,16-dimalonate). The macrocyclic complexes are much more stable against oxidn. than [EuII(DTPA)(H2O)]3- (the redox potentials are E1/2 = -0.82 V, -0.92 V, and -1.35 V vs. Ag/AgCl electrode for [EuIII/II(ODDA)(H2O)], [EuIII/II(ODDM)], and [EuIII/II(DTPA)(H2O)], resp., compared with -0.63 V for EuIII/II aqua). The thermodn. stability consts. of [EuII(ODDA)(H2O)], [EuII(ODDM)]2-, [Sr(ODDA)(H2O)], and [Sr(ODDM)]2- were also detd. by pH potentiometry. They are slightly higher for the EuII complexes than those for the corresponding Sr analogs (logKML = 9.85, 13.07, 8.66, and 11.34 for [EuII(ODDA)(H2O)], [EuII(ODDM)]2-, [Sr(ODDA)(H2O)], and [Sr(ODDM)]2-, resp., 0.1 M (CH3)4NCl). The increased thermodn. and redox stability of the EuII complex formed with ODDA as compared with the traditional ligand DTPA can be of importance when biomedical application is concerned. A variable-temp. 17O-NMR and 1H-nuclear magnetic relaxation dispersion (NMRD) study has been performed on [EuII(ODDA)(H2O)] and [EuII(ODDM)]2- in aq. soln. [EuII(ODDM)]2- has no inner-sphere water mol. which allowed us to use it as an outer-sphere model for [EuII(ODDA)(H2O)]. The water exchange rate (kex298 = 0.43 × 109 s-1) is one third of that obtained for [EuII(DTPA)(H2O)]3-. The variable pressure 17O-NMR study yielded a neg. activation vol., Δν = -3.9 cm3mol-1; this indicates associatively activated water exchange. This water exchange rate is in the optimal range to attain max. proton relaxivities, which are, however, strongly limited by the fast rotation of the small mol. wt. complex.
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Dovrat, G.; Pevzner, S.; Maimon, E.; Vainer, R.; Iliashevsky, O.; Ben-Eliyahu, Y.; Moisy, P.; Bettelheim, A.; Zilbermann, I. DOTP versus DOTA as Ligands for Lanthanide Cations: Novel Structurally Characterized Ce^IV and Ce^III Cyclen-Based Complexes and Clusters in Aqueous Solutions. Chem. – Eur. J. 2022, 28 (61), e20221868 DOI: 10.1002/chem.202201868
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Rodríguez-Rodríguez, A.; Regueiro-Figueroa, M.; Esteban-Gómez, D.; Rodríguez-Blas, T.; Patinec, V.; Tripier, R.; Tircsó, G.; Carniato, F.; Botta, M.; Platas-Iglesias, C. Definition of the Labile Capping Bond Effect in Lanthanide Complexes. Chem. – Eur. J. 2017, 23 (5), 1110– 1117, DOI: 10.1002/chem.201604390
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Definition of the Labile Capping Bond Effect in Lanthanide Complexes
Rodriguez-Rodriguez, Aurora; Regueiro-Figueroa, Martin; Esteban-Gomez, David; Rodriguez-Blas, Teresa; Patinec, Veronique; Tripier, Raphael; Tircso, Gyula; Carniato, Fabio; Botta, Mauro; Platas-Iglesias, Carlos
Chemistry - A European Journal (2017), 23 (5), 1110-1117CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)
Two macrocyclic ligands contg. a cyclen unit, a Me group, a picolinate arm, and two acetate pendant arms attached to two nitrogen atoms of the macrocycle either in trans (1,7-H3Medo2 ampa = 2,2'-(7-((6-carboxypyridin-2-yl)methyl)-10-methyl-1,4,7,10-tetraazacyclododecane-1,4-diyl)diacetic acid) or in cis (1,4-H3Medo2 ampa) positions are reported. These ligands provide eight-coordination to the Ln3+ ions, leaving a coordination position available for a water mol. that occupies a capping position in the twisted square antiprismatic polyhedron (1,4-H3Medo2 ampa) or one of the positions of the square antiprism (1,7-H3Medo2 ampa). The charge neutral [Gd(1,7-Medo2 ampa)] complex presents an unprecedentedly low water-exchange rate (kex298=8.8 × 103 s-1), whereas water exchange in [Gd(1,4-Medo2 ampa)] is three orders of magnitude faster (kex298=6.6 × 106 s-1). These results showcase the labile capping bond phenomenon: A ligand occupying a capping position is hindered by the environment and thus is intrinsically labile.
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Caravan, P.; Esteban-Gómez, D.; Rodríguez-Rodríguez, A.; Platas-Iglesias, C. Water Exchange in Lanthanide Complexes for MRI Applications. Lessons Learned over the Last 25 Years. Dalton Trans. 2019, 48 (30), 11161– 11180, DOI: 10.1039/C9DT01948K
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Water exchange in lanthanide complexes for MRI applications. Lessons learned over the last 25 years
Caravan, Peter; Esteban-Gomez, David; Rodriguez-Rodriguez, Aurora; Platas-Iglesias, Carlos
Dalton Transactions (2019), 48 (30), 11161-11180CODEN: DTARAF; ISSN:1477-9226. (Royal Society of Chemistry)
The water exchange rates of water mols. coordinated to the metal ion in lanthanide complexes have been profusely investigated during the last 25 years, esp. in the case of Gd3+ and Eu3+ complexes. This is mainly related to the important application of some Gd3+ complexes as contrast agents in magnetic resonance imaging (MRI), and the intensive investigation of Eu3+ complexes as contrast agent candidates providing contrast through the chem. exchange satn. transfer mechanism (CEST). Both applications require a fine tunning of the exchange rate of the coordinated water mol. to yield optimal response. Herein we review the progress made in this field to control water exchange in a rational way through ligand design, providing relationships between the obsd. trends, the structures of the complexes and the mechanisms responsible for the water exchange reaction.
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Garda, Z.; Nagy, V.; Rodríguez-Rodríguez, A.; Pujales-Paradela, R.; Patinec, V.; Angelovski, G.; Tóth, É.; Kálmán, F. K.; Esteban-Gómez, D.; Tripier, R.; Platas-Iglesias, C.; Tircsó, G. Unexpected Trends in the Stability and Dissociation Kinetics of Lanthanide(III) Complexes with Cyclen-Based Ligands across the Lanthanide Series. Inorg. Chem. 2020, 59 (12), 8184– 8195, DOI: 10.1021/acs.inorgchem.0c00520
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Unexpected Trends in the Stability and Dissociation Kinetics of Lanthanide(III) Complexes with Cycle-Based Ligands across the Lanthanide Series
Garda, Zoltan; Nagy, Viktoria; Rodriguez-Rodriguez, Aurora; Pujales-Paradela, Rosa; Patinec, Veronique; Angelovski, Goran; Toth, Eva; Kalman, Ferenc K.; Esteban-Gomez, David; Tripier, Raphael; Platas-Iglesias, Carlos; Tircso, Gyula
Inorganic Chemistry (2020), 59 (12), 8184-8195CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
We report a detailed study of the thermodn. stability and dissocn. kinetics of lanthanide complexes with two ligands contg. a cyclen unit, a Me group, a picolinate arm, and two acetate pendant arms linked to two nitrogen atoms of the macrocycle in either cis (1,4-H3DO2APA) or trans (1,7-H3DO2APA) positions. The stability consts. of the Gd3+ complexes with these two ligands are very similar, with log KGdL values of 16.98 and 16.33 for the complexes of 1,4-H3DO2APA and 1,7-H3DO2APA, resp. The stability consts. of complexes with 1,4-H3DO2APA follow the usual trend, increasing from log KLaL = 15.96 to log KLuL = 19.21. However, the stability of [Ln(1,7-DO2APA)] complexes decreases from log K = 16.33 for Gd3+ to 14.24 for Lu3+. The acid-catalyzed dissocn. rates of the Gd3+ complexes differ by a factor of ∼ 15, with rate consts. (k1) of 1.42 and 23.5 M-1 s-1 for [Gd(1,4-DO2APA)] and [Gd(1,7-DO2APA)], resp. This difference is magnified across the lanthanide series to reach a 5 orders of magnitude higher k1 for [Yb(1,7-DO2APA)] (1475 M-1 s-1) than for [Yb(1,4-DO2APA)] (5.79 x 10-3 M-1 s-1). The acid-catalyzed mechanism involves the protonation of a carboxylate group, followed by a cascade of proton-transfer events that result in the protonation of a nitrogen atom of the cyclen unit. D. functional theory calcns. suggest a correlation between the strength of the Ln-Ocarboxylate bonds and the kinetic inertness of the complex, with stronger bonds providing more inert complexes. The 1H NMR resonance of the coordinated water mol. in the [Yb(1,7-DO2APA)] complex at 176 ppm provides a sizable chem. exchange satn. transfer effect thanks to a slow water exchange rate of (15.9 ± 1.6) x 103 s-1. The arrangement of the ligand donor atoms around the lanthanide ion provokes dramatic differences in the thermodn. stabilities and dissocn. kinetics of lanthanide complexes, as demonstrated by investigating the complexes with two isomeric cyclen-based ligands, contg. a picolinate arm and two acetate arms in either positions 1,7 or 1,4 of the macrocyclic structure.
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Jannin, S.; Helm, L.; Bodenhausen, G. Kinetics of Yttrium–Ligand Complexation Monitored Using Hyperpolarized ⁸⁹ Y as a Model for Gadolinium in Contrast Agents. J. Am. Chem. Soc. 2010, 132 (14), 5006– 5007, DOI: 10.1021/ja1013954
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Kinetics of Yttrium-Ligand Complexation Monitored Using Hyperpolarized 89Y as a Model for Gadolinium in Contrast Agents
Mieville, Pascal; Jannin, Sami; Helm, Lothar; Bodenhausen, Geoffrey
Journal of the American Chemical Society (2010), 132 (14), 5006-5007CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
Hyperpolarization by dissoln. dynamic nuclear polarization (DNP) enhances 89Y spin magnetization by 3 to 4 orders of magnitude and provides a way to monitor yttrium-ligand complexation "on the fly" by means of 89Y NMR. In this communication, we show an example of free yttrium Y3+ being complexed with 1,4,7,10-tetrakis(acetamido)-1,4,7,10-tetraazacyclododecane (DOTAM) to form [Y(DOTAM)(H2O)]3+ as a model for gadolinium in contrast agents.
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Tickner, B. J.; Stasiuk, G. J.; Duckett, S. B.; Angelovski, G. The Use of Yttrium in Medical Imaging and Therapy: Historical Background and Future Perspectives. Chem. Soc. Rev. 2020, 49 (17), 6169– 6185, DOI: 10.1039/C9CS00840C
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The use of yttrium in medical imaging and therapy: historical background and future perspectives
Tickner Ben J; Stasiuk Graeme J; Duckett Simon B; Angelovski Goran
Chemical Society reviews (2020), 49 (17), 6169-6185 ISSN:.
Yttrium is a chemically versatile rare earth element that finds use in a range of applications including lasers and superconductors. In medicine, yttrium-based materials are used in medical lasers and biomedical implants. This is extended through the array of available yttrium isotopes to enable roles for (90)Y complexes as radiopharmaceuticals and (86)Y tracers for positron emission tomography (PET) imaging. The naturally abundant isotope (89)Y is proving to be suitable for nuclear magnetic resonance investigations, where initial reports in the emerging field of hyperpolarised magnetic resonance imaging (MRI) are promising. In this review we explore the coordination and radiochemical properties of yttrium, and its role in drugs for radiotherapy, PET imaging agents and perspectives for applications in hyperpolarised MRI.
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Vaughn, B. A.; Koller, A. J.; Chen, Z.; Ahn, S. H.; Loveless, C. S.; Cingoranelli, S. J.; Yang, Y.; Cirri, A.; Johnson, C. J.; Lapi, S. E.; Chapman, K. W.; Boros, E. Homologous Structural, Chemical, and Biological Behavior of Sc and Lu Complexes of the Picaga Bifunctional Chelator: Toward Development of Matched Theranostic Pairs for Radiopharmaceutical Applications. Bioconjugate Chem. 2021, 32 (7), 1232– 1241, DOI: 10.1021/acs.bioconjchem.0c00574
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Homologous Structural, Chemical, and Biological Behavior of Sc and Lu Complexes of the Picaga Bifunctional Chelator: Toward Development of Matched Theranostic Pairs for Radiopharmaceutical Applications
Vaughn, Brett A.; Koller, Angus J.; Chen, Zhihengyu; Ahn, Shin Hye; Loveless, C. Shaun; Cingoranelli, Shelbie J.; Yang, Yi; Cirri, Anthony; Johnson, Christopher J.; Lapi, Suzanne E.; Chapman, Karena W.; Boros, Eszter
Bioconjugate Chemistry (2021), 32 (7), 1232-1241CODEN: BCCHES; ISSN:1043-1802. (American Chemical Society)
The radioactive isotopes scandium-44/47 and lutetium-177 are gaining relevance for radioimaging and radiotherapy, resulting in a surge of studies on their coordination chem. and subsequent applications. Although the trivalent ions of these elements are considered close homologues, dissimilar chem. behavior is obsd. when they are complexed by large ligand architectures due to discrepancies between Lu(III) and Sc(III) ions with respect to size, chem. hardness, and Lewis acidity. Here, authors demonstrate that Lu and Sc complexes of 1,4-bis(methoxycarbonyl)-7-[(6-carboxypyridin-2-yl)methyl]-1,4,7-triazacyclononane (H3mpatcn) and its corresponding bioconjugate picaga-DUPA can be employed to promote analogous structural features and, subsequently, biol. properties for coordination complexes of these ions. The close homol. was evidenced using potentiometric methods, computational modeling, variable temp. mass spectrometry, and pair distribution function anal. of x-ray scattering data. Radiochem. labeling, in vitro stability, and biodistribution studies with Sc-47 and Lu-177 indicate that the 7-coordinate ligand environment of the bifunctional picaga ligand is compatible with biol. applications and the future investigation of β-emitting, picaga-chelated Sc and Lu isotopes for radiotherapy.
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Caravan, P.; Ellison, J. J.; McMurry, T. J.; Lauffer, R. B. Gadolinium(III) Chelates as MRI Contrast Agents: Structure, Dynamics, and Applications. Chem. Rev. 1999, 99 (9), 2293– 2352, DOI: 10.1021/cr980440x
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Gadolinium(III) Chelates as MRI Contrast Agents: Structure, Dynamics, and Applications
Caravan, Peter; Ellison, Jeffrey J.; McMurry, Thomas J.; Lauffer, Randall B.
Chemical Reviews (Washington, D. C.) (1999), 99 (9), 2293-2352CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
A review with 343 refs. on gadolinium(III) chelates judged to be of sufficient stability for in vivo use. Topics covered include soln. and solid state structures, relaxation theory, phys. properties, and macromol. conjugates.
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Le Fur, M.; Molnár, E.; Beyler, M.; Kálmán, F. K.; Fougère, O.; Esteban-Gómez, D.; Rousseaux, O.; Tripier, R.; Tircsó, G.; Platas-Iglesias, C. A Coordination Chemistry Approach to Fine-Tune the Physicochemical Parameters of Lanthanide Complexes Relevant to Medical Applications. Chem. – Eur. J. 2018, 24 (13), 3127– 3131, DOI: 10.1002/chem.201705528
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A Coordination Chemistry Approach to Fine-Tune the Physicochemical Parameters of Lanthanide Complexes Relevant to Medical Applications
Le Fur, Mariane; Molnar, Eniko; Beyler, Maryline; Kalman, Ferenc K.; Fougere, Olivier; Esteban-Gomez, David; Rousseaux, Olivier; Tripier, Raphael; Tircso, Gyula; Platas-Iglesias, Carlos
Chemistry - A European Journal (2018), 24 (13), 3127-3131CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)
The geometric features of two pyclen-based ligands possessing identical donor atoms but different site organization have a profound impact in their complexation properties toward lanthanide ions. The ligand contg. two acetate groups and a picolinate arm arranged in a sym. fashion (L1) forms a Gd3+ complex being two orders of magnitude less stable than its dissym. analog GdL2. Besides, GdL1 experiences a much faster dissocn. following the acid-catalyzed mechanism than GdL2. On the contrary, GdL1 exhibits a lower exchange rate of the coordinated water mol. compared to GdL2. These very different properties are related to different strengths of the Gd-ligand bonds assocd. to steric effects, which hinder the coordination of a water mol. in GdL2 and the binding of acetate groups in GdL1.
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Roca-Sabio, A.; Regueiro-Figueroa, M.; Esteban-Gómez, D.; de Blas, A.; Rodríguez-Blas, T.; Platas-Iglesias, C. Density Functional Dependence of Molecular Geometries in Lanthanide(III) Complexes Relevant to Bioanalytical and Biomedical Applications. Comput. Theor. Chem. 2012, 999, 93– 104, DOI: 10.1016/j.comptc.2012.08.020
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Density functional dependence of molecular geometries in lanthanide(III) complexes relevant to bioanalytical and biomedical applications
Roca-Sabio, Adrian; Regueiro-Figueroa, Martin; Esteban-Gomez, David; de Blas, Andres; Rodriguez-Blas, Teresa; Platas-Iglesias, Carlos
Computational & Theoretical Chemistry (2012), 999 (), 93-104CODEN: CTCOA5; ISSN:2210-271X. (Elsevier B.V.)
A set of 15 lanthanide-contg. model systems was used to evaluate the performance of 15 commonly available d. functionals (SVWN, SPL, BLYP, G96LYP, mPWLYP, B3LYP, BH&HLYP, B3PW91, BB95, mPWB95, TPSS, TPSSh, M06, CAM-B3LYP and wB97XD) in geometry detn., benchmarked against MP2 calcns. The best agreement between DFT optimized geometries and those obtained from MP2 calcns. is provided by meta-GGA and hybrid meta-GGA functionals. The use of hybrid-GGA functionals such as BH&HLYP and B3PW91 also provide reasonably good results, while B3LYP provides an important overestimation of the metal-ligand bonds. The performance of different basis sets to describe the ligand(s) atoms, as well as the use of large-core (LC) RECPs and small-core (SC) RECPs, has been also assessed. Our calcns. show that SCRECP calcns. provide somewhat shorter GdIII-donor distances than the LCRECP approach, the av. contraction of bond distances for the systems investigated amounting to 0.033 Å. However, geometry optimizations with the SCRECP (in combination with the mPWB95 functional and the 6-31G(d) basis set for the ligand atoms) take about 15 times longer than the LC counterparts, and about four times longer than MP2/LCRECP/6-31G(d) calcns. The 6-31G(d), 6-311G(d), 6-311G(d,p) or cc-pVDZ basis sets, in combination with LCRECPs, appear to offer an adequate balance between accuracy and computational cost for the description of mol. geometries of LnIII complexes. Electronic energies calcd. with the the cc-pVxZ family (x = D-6) indicate a relative fast convergence to the complete basis set (CBS) limit with basis set size. The inclusion of bulk solvent effects (IEFPCM) was shown to provoke an important impact on the calcd. geometries, particularly on the metal-nitrogen distances. Calcns. performed on lanthanide complexes relevant for practical applications confirmed the important effect of the solvent on the calcd. geometries.
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Inoue, M. B.; Inoue, M.; Muñoz, I. C.; Bruck, M. A.; Fernando, Q. Syntheses of New 15-Membered and 16-Membered Macrocyclic Ligands with Three Pendant Acetato Groups and the Structures of the Gadolinium(III) Complexes. Inorg. Chim. Acta 1993, 209, 29– 34, DOI: 10.1016/S0020-1693(00)84976-2
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Syntheses of new 15-membered and 16-membered macrocyclic ligands with three pendant acetato groups and the structures of the gadolinium(III) complexes
Inoue, Michiko B.; Inoue, Motomichi; Munoz, Iliana C.; Bruck, Michael A.; Fernando, Quintus
Inorganica Chimica Acta (1993), 209 (1), 29-34CODEN: ICHAA3; ISSN:0020-1693.
A condensation of diethylenetriaminepentaacetic dianhydride with ethylenediamine gave a 15-membered macrocyclic ligand with 3 pendant acetato groups, (15-dtpa-en)H3 = C10H18N5O2(CH2CO2H)3; a 16-membered analog, (16-dtpa-pn)H3 = C11H20N5O2(CH2CO2H)3, was obtained using 1,3-propanediamine instead of ethylenediamine. The structures of their Gd(III) complexes, Gd2(15-dtpa-en)2.16H2O and Gd(16-dtpa-pn).4H2O, were detd. by x-ray analyses. Gd2(15-dtpa-en)2.16H2O crystd. as orthorhombic, space group Pbca, a 18.205(1), b 18.930(1), c 15.609(1) Å, Z = 4, R = 0.026, Rw = 0.042. Two Gd(III) ions are located between 2 ligand mols., forming a binuclear metal chelate mol. with a center of inversion. The coordination geometry around a metal ion is described as a distorted tricapped trigonal prism that consists of 9 coordinated atoms. Gd(16-dtpa-pn).4H2O crystd. as monoclinic, space group P21/c, a 8.246(2), b 14.995(3), c 19.367(4) Å, β 90.258(2)°, Z = 4, R = 0.021, Rw = 0.035. In this compd., a H2O mol. and a single ligand mol. are coordinated to a Gd(III), forming a mononuclear chelate with a tricapped trigonal prism. The structural differences between the 2 Gd(III) complexes are a result of the differences in the favorable conformations assumed by the 2 macrocyclic ligands.
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Bader, R. F. W.; Carroll, M. T.; Cheeseman, J. R.; Chang, C. Properties of Atoms in Molecules: Atomic Volumes. J. Am. Chem. Soc. 1987, 109 (26), 7968– 7979, DOI: 10.1021/ja00260a006
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Properties of atoms in molecules: atomic volumes
Bader, Richard F. W.; Carroll, Marshall T.; Cheeseman, James R.; Chang, Cheng
Journal of the American Chemical Society (1987), 109 (26), 7968-79CODEN: JACSAT; ISSN:0002-7863.
The theory of atoms in mols. defines an atom and the av. values of its properties. The intersection of an at. surface, as defined by a property of the charge d., with a particular envelope of the charge d. defines the vol. of an atom in a mol. The value of the d. envelope used to bound the open portion of an at. region can be chosen on the basis of comparison with measured properties. The nature of the results are, in any event, independent of the choice for envelopes which contain >96% of the total electronic charge and lie within the usual range of van der Waals contact distances. It is shown that the vols. of Me and methylene groups in normal hydrocarbons are transferable properties, as are their charge distributions, populations, and energies. The vol. of a C atom subject to steric crowding decreases as its stability and electron population increase. This behavior is opposite to that found for a C atom in a system with geometric strain as found in cyclic and bicyclic mols. The stability, population, and vol. of a C atom all undergo parallel increases as the atom is subjected to an increasing degree of geometric strain. The vols. of the bridgehead C atoms in bicyclo[1.1.0]butane and [1.1.1]propellane are 1.2 and 1.5 times, resp., the vol. of a Me C atom. As anticipated on the basis of the orbital model, an increase in geometric strain is correlated with an increase in s character and thus finds the electron population, stability, and vol. of a C atom to undergo the same parallel increases in value through the series ethane, ethylene, acetylene. As a first step in the investigation of how atoms fit together, the changes in the at. vols. accompanying the formation of a H bond are detd.
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Neese, F. The ORCA Program System. WIREs Comput. Mol. Sci. 2012, 2 (1), 73– 78, DOI: 10.1002/wcms.81
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The ORCA program system
Neese, Frank
Wiley Interdisciplinary Reviews: Computational Molecular Science (2012), 2 (1), 73-78CODEN: WIRCAH; ISSN:1759-0884. (Wiley-Blackwell)
A review. ORCA is a general-purpose quantum chem. program package that features virtually all modern electronic structure methods (d. functional theory, many-body perturbation and coupled cluster theories, and multireference and semiempirical methods). It is designed with the aim of generality, extendibility, efficiency, and user friendliness. Its main field of application is larger mols., transition metal complexes, and their spectroscopic properties. ORCA uses std. Gaussian basis functions and is fully parallelized. The article provides an overview of its current possibilities and documents its efficiency.
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Neese, F. Software Update: The ORCA Program System, Version 4.0. WIREs Comput. Mol. Sci. 2018, 8 (1), e1327 DOI: 10.1002/wcms.1327
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Reiher, M. Douglas–Kroll–Hess Theory: A Relativistic Electrons-Only Theory for Chemistry. Theor. Chem. Acc. 2006, 116 (1–3), 241– 252, DOI: 10.1007/s00214-005-0003-2
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Douglas-Kroll-Hess Theory: A relativistic electrons-only theory for chemistry
Reiher, Markus
Theoretical Chemistry Accounts (2006), 116 (1-3), 241-252CODEN: TCACFW; ISSN:1432-881X. (Springer GmbH)
A review. A unitary transformation allows to sep. (block-diagonalize) the Dirac Hamiltonian into two parts one part: solely describes electrons, while the other gives rise to neg.-energy states, which are the so-called positronic states. The block-diagonal form of the Hamiltonian no longer accounts for the coupling of both kinds of states. The pos.-energy ('electrons-only') part can serve as a 'fully' relativistic electrons-only theory, which can be understood as a rigorous basis for chem. Recent developments of the Douglas-Kroll-Hess (DKH) method allowed to derive a sequence of expressions, which approx. this electrons-only Hamiltonian up to arbitrary-order. While all previous work focused on the numerical stability and accuracy of these arbitrary-order DKH Hamiltonians, conceptual issues and paradoxa of the method were mostly left aside. In this work, the conceptual side of DKH theory is revisited in order to identify essential aspects of the theory to be distinguished from purely computational consideration.
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Chai, J.-D.; Head-Gordon, M. Long-Range Corrected Hybrid Density Functionals with Damped Atom–Atom Dispersion Corrections. Phys. Chem. Chem. Phys. 2008, 10 (44), 6615– 6620, DOI: 10.1039/b810189b
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Long-range corrected hybrid density functionals with damped atom-atom dispersion corrections
Chai, Jeng-Da; Head-Gordon, Martin
Physical Chemistry Chemical Physics (2008), 10 (44), 6615-6620CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
We report re-optimization of a recently proposed long-range cor. (LC) hybrid d. functional [J.-D. Chai and M. Head-Gordon, J. Chem. Phys., 2008, 128, 084106] to include empirical atom-atom dispersion corrections. The resulting functional, ωB97X-D yields satisfactory accuracy for thermochem., kinetics, and non-covalent interactions. Tests show that for non-covalent systems, ωB97X-D shows slight improvement over other empirical dispersion-cor. d. functionals, while for covalent systems and kinetics it performs noticeably better. Relative to our previous functionals, such as ωB97X, the new functional is significantly superior for non-bonded interactions, and very similar in performance for bonded interactions.
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Chai, J.-D.; Head-Gordon, M. Systematic Optimization of Long-Range Corrected Hybrid Density Functionals. J. Chem. Phys. 2008, 128 (8), 084106 DOI: 10.1063/1.2834918
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Systematic optimization of long-range corrected hybrid density functionals
Chai, Jeng-Da; Head-Gordon, Martin
Journal of Chemical Physics (2008), 128 (8), 084106/1-084106/15CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)
A general scheme for systematically modeling long-range cor. (LC) hybrid d. functionals is proposed. Our resulting two LC hybrid functionals are shown to be accurate in thermochem., kinetics, and noncovalent interactions, when compared with common hybrid d. functionals. The qual. failures of the commonly used hybrid d. functionals in some "difficult problems," such as dissocn. of sym. radical cations and long-range charge-transfer excitations, are significantly reduced by the present LC hybrid d. functionals. (c) 2008 American Institute of Physics.
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Najibi, A.; Goerigk, L. The Nonlocal Kernel in van Der Waals Density Functionals as an Additive Correction: An Extensive Analysis with Special Emphasis on the B97M-V and ωB97M-V Approaches. J. Chem. Theory Comput. 2018, 14 (11), 5725– 5738, DOI: 10.1021/acs.jctc.8b00842
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The Nonlocal Kernel in van der Waals Density Functionals as an Additive Correction: An Extensive Analysis with Special Emphasis on the B97M-V and ωB97M-V Approaches
Najibi, Asim; Goerigk, Lars
Journal of Chemical Theory and Computation (2018), 14 (11), 5725-5738CODEN: JCTCCE; ISSN:1549-9618. (American Chemical Society)
The development of van der Waals d. functional approxns. (vdW-DFAs) has gained considerable interest over the past decade. While in a strictest sense, energy calcns. with vdW-DFAs should be carried out fully self-consistently, we demonstrate conclusively for a total of 11 methods that such a strategy only increases the computational time effort without having any significant effect on energetic properties, electron densities, or orbital-energy differences. The strategy to apply a nonlocal vdW-DFA kernel as an additive correction to a fully converged conventional DFA result is therefore justified and more efficient. As part of our study, we utilize the extensive GMTKN55 database for general main-group thermochem., kinetics, and noncovalent interactions [Phys. Chem. Chem. Phys.2017, 19, 32184], which allows us to analyze the very promising B97M-V [J. Chem. Phys. 2015, 142, 074111] and ωB97M-V [J. Chem. Phys. 2016, 144, 214110] DFAs. We also present new DFT-D3(BJ) based counterparts of these two methods and of ωB97X-V [J. Chem. Theory Comput 2013, 9, 263], which are faster variants with similar accuracy. Our study concludes with updated recommendations for the general method user, based on our current overview of 325 dispersion-cor. and -uncorrected DFA variants analyzed for GMTKN55. VdW-DFAs are the best representatives of the three highest rungs of Jacob's Ladder, namely, B97M-V, ωB97M-V, and DSD-PBEP86-NL.
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Weigend, F.; Ahlrichs, R. Balanced Basis Sets of Split Valence, Triple Zeta Valence and Quadruple Zeta Valence Quality for H to Rn: Design and Assessment of Accuracy. Phys. Chem. Chem. Phys. 2005, 7 (18), 3297– 3305, DOI: 10.1039/b508541a
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Balanced basis sets of split valence, triple zeta valence and quadruple zeta valence quality for H to Rn: Design and assessment of accuracy
Weigend, Florian; Ahlrichs, Reinhart
Physical Chemistry Chemical Physics (2005), 7 (18), 3297-3305CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
Gaussian basis sets of quadruple zeta valence quality for Rb-Rn are presented, as well as bases of split valence and triple zeta valence quality for H-Rn. The latter were obtained by (partly) modifying bases developed previously. A large set of more than 300 mols. representing (nearly) all elements-except lanthanides-in their common oxidn. states was used to assess the quality of the bases all across the periodic table. Quantities investigated were atomization energies, dipole moments and structure parameters for Hartree-Fock, d. functional theory and correlated methods, for which we had chosen Moller-Plesset perturbation theory as an example. Finally recommendations are given which type of basis set is used best for a certain level of theory and a desired quality of results.
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Pantazis, D. A.; Neese, F. All-Electron Scalar Relativistic Basis Sets for the Lanthanides. J. Chem. Theor. Comput. 2009, 5 (9), 2229– 2238, DOI: 10.1021/ct900090f
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All-electron scalar relativistic basis sets for the lanthanides
Pantazis, Dimitrios A.; Neese, Frank
Journal of Chemical Theory and Computation (2009), 5 (9), 2229-2238CODEN: JCTCCE; ISSN:1549-9618. (American Chemical Society)
Segmented all-electron relativistically contracted (SARC) basis sets are constructed for the elements 57La-71Lu and optimized for d. functional theory (DFT) applications. The basis sets are intended for use in combination with the DKH2 or ZORA scalar relativistic Hamiltonians for which individually optimized contractions are provided. Significant computational advantages can be realized owing to the loose contraction of the SARC basis sets compared to generally contracted basis sets, while their compact size allows them to replace effective core potentials for routine studies of lanthanide complexes. The new basis sets are evaluated in DFT calcns. of the first four ionization energies of the lanthanides. They yield results that accurately reproduce the exptl. trends, confirming a balanced treatment of different electronic configurations. The performance of the basis sets is further assessed in mol. systems with a comprehensive study of the lanthanide trihalides. Despite their compact size, the SARC basis sets demonstrate consistent, efficient, and reliable performance and will be esp. useful in calcns. of mol. properties that require explicit treatment of the core electrons.
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Bader, R. F. W. Atoms in Molecules. Acc. Chem. Res. 1985, 18, 9– 15, DOI: 10.1021/ar00109a003
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Atoms in molecules
Bader, R. F. W.
Accounts of Chemical Research (1985), 18 (1), 9-15CODEN: ACHRE4; ISSN:0001-4842.
A review with 21 refs.
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Tosi, M. P.; Fumi, F. G. Ionic Sizes And Born Repulsive Parameters In The NaCl-Type Alkali Halides-II: The Generalized Huggins-Mayer Form. J. Phys. Chem. Solids 1964, 25, 45– 52, DOI: 10.1016/0022-3697(64)90160-X
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Ionic sizes and Born repulsive parameters in the NaCl-type alkali halides. II. Generalized Huggins-Mayer forms
Tosi, M. P.; Fumi, F. G.
Journal of Physics and Chemistry of Solids (1964), 25 (1), 45-52CODEN: JPCSAW; ISSN:0022-3697.
The procedure described for the detn. of the crystal radii of the ions in the individual NaCl-type alkali halides from solid-state data by the Born model is applied, adopting a generalized Huggins-Mayer form for the Born repulsive energy (i.e. allowing the hardness parameter to vary from salt to salt). The resulting values of the crystal radii agree within 0.05 A. with the values obtained with the Huggins-Mayer and Pauling forms. This indicates that the Born model, irrespective of the specific plausible form adopted for the Born repulsive energy, leads to relative values of the crystal radii for the alkali and halogen ions in the NaCl structure exceeding by ∼0.3 A. the traditional relative values, which refer to nearly free ions. Qual. and quant. evidence supporting these ionic deformations is discussed.
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Pauling, L. The Sizes of Ions and the Structure of Ionic Crystals. J. Am. Chem. Soc. 1927, 49 (3), 765– 790, DOI: 10.1021/ja01402a019
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Sizes of ions and structure of ionic crystals
Pauling, Linus
Journal of the American Chemical Society (1927), 49 (), 765-92CODEN: JACSAT; ISSN:0002-7863.
With an at. model derived from the wave mechanics of Schr.ovrddot.odinger, size-screening consts. have been calcd. for the electrons in many-electron atoms and ions. After a discussion of the forces between ions, and of the significance of ionic sizes, values of the univalent crystal radius and the crystal radius are derived for a large no. of ions with the aid of these screening consts., using as a starting point the observed inter-atomic distances in crystals of NaF, KCl, RbBr, CsI and Li2O. The theoretical result is derived that ionic compds. MX2 will crystallize with fluorite structure if the radius ratio RM/RX is greater than 0.65, and with the rutile (or anatase) structure if it is less. This result is exptly. substantiated. Theoretically a binary compd. should have the sphalerite or wurzite structure instead of the NaCl structure if the radius ratio is less than 0.33. The oxide, sulfide, selenide and telluride of Be conform to this requirement, and are to be considered as ionic crystals. It is found, however, that such "tetrahedral" crystals are particularly apt to Show deformation, and it is suggested that this is a tendency of the anion to share an electron pair. with each cation.
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Lu, T.; Chen, F. Multiwfn: A Multifunctional Wavefunction Analyzer. J. Comput. Chem. 2012, 33 (5), 580– 592, DOI: 10.1002/jcc.22885
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Multiwfn: A multifunctional wavefunction analyzer
Lu, Tian; Chen, Feiwu
Journal of Computational Chemistry (2012), 33 (5), 580-592CODEN: JCCHDD; ISSN:0192-8651. (John Wiley & Sons, Inc.)
Multiwfn is a multifunctional program for wavefunction anal. Its main functions are: (1) Calcg. and visualizing real space function, such as electrostatic potential and electron localization function at point, in a line, in a plane or in a spatial scope. (2) Population anal. (3) Bond order anal. (4) Orbital compn. anal. (5) Plot d.-of-states and spectrum. (6) Topol. anal. for electron d. Some other useful utilities involved in quantum chem. studies are also provided. The built-in graph module enables the results of wavefunction anal. to be plotted directly or exported to high-quality graphic file. The program interface is very user-friendly and suitable for both research and teaching purpose. The code of Multiwfn is substantially optimized and parallelized. Its efficiency is demonstrated to be significantly higher than related programs with the same functions. Five practical examples involving a wide variety of systems and anal. methods are given to illustrate the usefulness of Multiwfn. The program is free of charge and open-source. Its precompiled file and source codes are available from http://multiwfn.codeplex.com. © 2011 Wiley Periodicals, Inc. J Comput Chem, 2011.
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Wada, A.; Watanabe, M.; Yamanoi, Y.; Nishihara, H. Modification of the Luminescence Spectra of Chloro(Tetrapyridylcyclotetramine)Europium Complexes by Fine Tuning of the Eu–Cl Distance with Outer-Sphere Counterions in the Solid State, in a Polymer Matrix and in Solution. Chem. Commun. 2008, 1671– 1673, DOI: 10.1039/b716987f
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Modification of the luminescence spectra of chloro(tetrapyridylcyclotetramine)europium complexes by fine tuning of the Eu-Cl distance with outer-sphere counterions in the solid state, in a polymer matrix and in solution
Wada, Atsushi; Watanabe, Masayuki; Yamanoi, Yoshinori; Nishihara, Hiroshi
Chemical Communications (Cambridge, United Kingdom) (2008), (14), 1671-1673CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
Controlling the coordination environments and the luminescence of Eu3+ complexes with outer-sphere counterions was achieved in the solid state, in a polymer matrix and in soln.
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Natrajan, L. S.; Khoabane, N. M.; Dadds, B. L.; Muryn, C. A.; Pritchard, R. G.; Heath, S. L.; Kenwright, A. M.; Kuprov, I.; Faulkner, S. Probing the Structure, Conformation, and Stereochemical Exchange in a Family of Lanthanide Complexes Derived from Tetrapyridyl-Appended Cyclen. Inorg. Chem. 2010, 49 (17), 7700– 7709, DOI: 10.1021/ic100447m
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Probing the Structure, Conformation, and Stereochemical Exchange in a Family of Lanthanide Complexes Derived from Tetrapyridyl-Appended Cyclen
Natrajan, Louise S.; Khoabane, Ntai M.; Dadds, Benjamin L.; Muryn, Christopher A.; Pritchard, Robin G.; Heath, Sarah L.; Kenwright, Alan M.; Kuprov, Ilya; Faulkner, Stephen
Inorganic Chemistry (2010), 49 (17), 7700-7709CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
A series of lanthanide complexes have been synthesized from 1,4,7,10-tetrakis(2-pyridylmethyl)-1,4,7,10-tetraazacyclododecane (LPy). Crystallog. studies indicate that, in the solid phase, all of the lanthanide ions are 9-coordinate and are bound to eight N atoms from the donor ligand, with the ninth site being filled by a counterion or solvent mol. In soln., time-resolved luminescence studies indicate that the luminescence exhibits contributions from two species corresponding to the nonhydrated and hydrated forms. The NMR spectra in protic media show two dominant isomers on the NMR time scale; furthermore, the spectra are very different from those obtained for 1,4,7,10-tetraazacyclododecane-N',N'',N''',N''''-tetraacetic acid (DOTA) and its derivs. The different forms of the complex undergo slow conformational and enantiomeric exchange in soln., which has been measured by NMR. The exchange path has been mapped out by d. functional theory calcns. and shows multiple metastable conformations (with respect to the dihedral angles of the cyclen ring). This contrasts with the established NMR behavior of DOTA complexes, which has been described by a two-state soln. equil.
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Gunnlaugsson, T.; Davies, R. J. H.; Kruger, P. E.; Jensen, P.; McCabe, T.; Mulready, S.; O’Brien, J. E.; Stevenson, C. S.; Fanning, A.-M. Cyclen Based Lanthanide Ion Ribonuclease Mimics: The Effect of Pyridine Cofactors upon Phosphodiester HPNP Hydrolysis. Tetrahedron Lett. 2005, 46 (21), 3761– 3766, DOI: 10.1016/j.tetlet.2005.03.150
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Cyclen based lanthanide ion ribonuclease mimics: the effect of pyridine cofactors upon phosphodiester HPNP hydrolysis
Gunnlaugsson, Thorfinnur; Davies, R. Jeremy H.; Kruger, Paul E.; Jensen, Paul; McCabe, Thomas; Mulready, Sinead; O'Brien, John E.; Stevenson, Clarke S.; Fanning, Ann-Marie
Tetrahedron Letters (2005), 46 (21), 3761-3766CODEN: TELEAY; ISSN:0040-4039. (Elsevier B.V.)
The cyclen based pyridine complexes 1Ln-3Ln (Ln = La(III) and Eu(III); 1-3 = N-(pyridin-x-yl)-2-[2,7,10-tris[(pyridin-x-ylcarbamoyl)methyl]-1,4,7,10-tetraazacyclododec-1-yl]acetamide (x = 2, 3, 4)) were synthesized as metallo-RNase mimics and their ability to hydrolytically cleave the phosphodiester of HPNP ((p-O2NC6H4O)(HOCHMeCH2O)PO2-) at 37° was studied using UV-visible spectroscopy, whereas the binding of the substrate was evaluated using 31P NMR and Eu(III)-luminescent measurements. In contrast 2Ln gave rise to fast pH dependent hydrolysis of HPNP, with max. efficiency at pH ∼8.2, and with a half-life of ∼1 h, the 1Ln and 3Ln complexes are inactive, emphasizing the importance of the nature of the pyridine isomer as a cofactor in the hydrolytic process. The crystal and mol. structures of the La, Eu and Gd complexes with the pyridin-3-yl-derived macrocycle were detd. by x-ray crystallog.
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Gao, J.; Ye, K.; He, M.; Xiong, W.-W.; Cao, W.; Lee, Z. Y.; Wang, Y.; Wu, T.; Huo, F.; Liu, X.; Zhang, Q. Tuning Metal–Carboxylate Coordination in Crystalline Metal–Organic Frameworks through Surfactant Media. J. Solid State Chem. 2013, 206, 27– 31, DOI: 10.1016/j.jssc.2013.07.031
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Tuning metal-carboxylate coordination in crystalline metal-organic frameworks through surfactant media
Gao, Junkuo; Ye, Kaiqi; He, Mi; Xiong, Wei-Wei; Cao, Wenfang; Lee, Zhi Yi; Wang, Yue; Wu, Tom; Huo, Fengwei; Liu, Xiaogang; Zhang, Qichun
Journal of Solid State Chemistry (2013), 206 (), 27-31CODEN: JSSCBI; ISSN:0022-4596. (Elsevier B.V.)
Although it was widely demonstrated that surfactants can efficiently control the size, shape and surface properties of micro/nanocrystals of metal-org. frameworks (MOFs) due to the strong interactions between surfactants and crystal facets of MOFs, the use of surfactants as reaction media to grow MOF single crystals is unprecedented. Compared with ionic liqs., surfactants are much cheaper and can have multifunctional properties such as acidic, basic, neutral, cationic, anionic, or even block. These factors strongly motivate the authors to develop a new synthetic strategy: growing cryst. MOFs in surfactants. Eight new two-dimensional (2D) or three-dimensional (3D) MOFs were successfully synthesized in an industrially-abundant and environmentally-friendly surfactant: polyethylene glycol-200 (PEG-200). Eight different coordination modes of carboxylates, ranging from monodentate η1 mode to tetra-donor coordination μ3-η1:η2:η1 mode, were founded in the authors' research. The magnetic properties of Co-based MOFs were studied and MOF NTU-Z6b showed a phase transition with a Curie temp. (Tc) at 5 K. The authors' strategy of growing cryst. MOFs in surfactant could offer exciting opportunities for prepg. novel MOFs with diverse structures and interesting properties.
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Gao, S.; George, S. J.; Zhou, Z.-H. Interaction of Gd-DTPA with Phosphate and Phosphite: Toward the Reaction Intermediate in Nephrogenic Systemic Fibrosis. Dalton Trans. 2016, 45 (12), 5388– 5394, DOI: 10.1039/C5DT04172D
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Interaction of Gd-DTPA with phosphate and phosphite: toward the reaction intermediate in nephrogenic systemic fibrosis
Gao, Song; George, Simon J.; Zhou, Zhao-Hui
Dalton Transactions (2016), 45 (12), 5388-5394CODEN: DTARAF; ISSN:1477-9226. (Royal Society of Chemistry)
Direct reactions of the MRI contrast agent K2[Gd(DTPA)(H2O)]·5H2O (1) (H5DTPA = diethylenetriaminepentaacetic acid) with dipotassium hydrogen phosphate (K2HPO4) or phosphite (K2HPO3) result in the isolation of well-defined Gd-DTPA phosphite K6[Gd2(DTPA)2(HPO3)]·7H2O (2) or phosphate K6[Gd2(DTPA)2(HPO4)]·10H2O (3), resp. Their lanthanum analogs K4[La2(DTPA)2(H2O)]·8H2O (4), K6[La2(DTPA)2(HPO3)]·7H2O (5) and K6[La2(DTPA)2(HPO4)]·10H2O (6) are used for comparison. The phosphate and phosphite groups are able to substitute the coordinated water mols. in 1 and 4 in a close physiol. aq. soln., and act as bridging ligands to link adjacent Ln(DTPA)2- (Ln = Gd and La) into dimeric structures. Solid state and soln. 13C NMR spectra of dimer 4 show complete dissocn. into its monomeric species in soln., while no dissocn. is obsd. for lanthanum phosphite 5 and phosphate 6 in soln., which show only one set of 13C spectra with the largest downfield shifts at 182.0 and 182.3 ppm resp. Comparisons of the bond distances and spectral data indicate that the interaction between DTPA and central Ln3+ cations are weakened after the substitutions, which support phosphate substituted Gd-DTPA as an initial intermediate in nephrogenic systemic fibrosis.
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Onate, C. A.; Okon, I. B.; Vincent, U. E.; Eyube, E. S.; Onyeaju, M. C.; Omugbe, E.; Egharevba, G. O. Non-Relativistic Molecular Modified Shifted Morse Potential System. Sci. Rep. 2022, 12 (1), 15188, DOI: 10.1038/s41598-022-19179-4
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Non-relativistic molecular modified shifted Morse potential system
Onate, C. A.; Okon, I. B.; Vincent, U. E.; Eyube, E. S.; Onyeaju, M. C.; Omugbe, E.; Egharevba, G. O.
Scientific Reports (2022), 12 (1), 15188CODEN: SRCEC3; ISSN:2045-2322. (Nature Portfolio)
Abstr.: A shifted Morse potential model is modified to fit the study of the vibrational energies of some mols. Using a traditional technique/methodol., the vibrational energy and the un-normalized radial wave functions were calcd. for the modified shifted Morse potential model. The condition that fits the modified potential for mol. description were deduced together with the expression for the screening parameter. The vibrational energies of SiC, NbO, CP, PH, SiF, NH and Cs2 mols. were computed by inserting their resp. spectroscopic consts. into the calcd. energy equation. It was shown that the calcd. results for all the mols. agreement perfectly with the exptl. RKR values. The present potential performs better than Improved Morse and Morse potentials for cesium dimer. Finally, the real Morse potential model was obtained as a special case of the modified shifted potential.
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Janicki, R.; Mondry, A. Structural and Thermodynamic Aspects of Hydration of Gd(iii) Systems. Dalton Trans. 2019, 48, 3380– 3391, DOI: 10.1039/C8DT04869J
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Structural and thermodynamic aspects of hydration of Gd(III) systems
Janicki, Rafal; Mondry, Anna
Dalton Transactions (2019), 48 (10), 3380-3391CODEN: DTARAF; ISSN:1477-9226. (Royal Society of Chemistry)
X-ray crystal structures of Gd(III) and Lu(III) aqua ions as well as their complexes with polyaminopolycarboxylates (EDTA, CDTA, EGTA, DTPA, DOTA) were detd.: [Gd(H2O)9](CF3SO3)3, [Gd(H2O)8]Cl3·C10H20O5, [Lu(H2O)8]Cl3·C12H24O6·4H2O, [C(NH2)3][Gd(EDTA)(H2O)3], [C(NH2)3]2[Lu(EDTA)(H2O)2]ClO4·6H2O, [C(NH2)3][Lu(CDTA)(H2O)2]·6H2O, [C(NH2)3][Gd(EGTA)(H2O)]·2H2O, [C(NH2)2(N2H4)][Gd(HDTPA)(H2O)]·2H2O, Na[Gd(DOTA)(H2O)]·4H2O, and K2[Lu(DOTA)]Cl·4.6H2O. The weighted sums of UV absorption spectra of appropriate crystals were used to reproduce the spectra of the Gd(III) aq. solns. in the temp. range 276-363 K. In aq. soln. the Gd(III)-EGTA, Gd(III)-DTPA and Gd(III)-DOTA complexes exist as almost pure monohydrate [GdL(H2O)]n- species, while in the case of the Gd(III) aqua ion, Gd(III)-EDTA and Gd(III)-CDTA systems the equil. between variously hydrated species were found. The derived molar fractions of these species were used to det. the ΔG, ΔH and ΔS of hydration. These thermodn. functions may be derived not only from the spectra of the hypersensitive transitions, but from other f-f transitions as well. Next the ΔG, ΔH and ΔS values of hydration for the other Ln(III)-EDTA systems (Ln = Pr, Nd, Sm, Eu) were detd. The ΔG298 values of the dehydration reaction for Ln(III)-EDTA complexes (Ln = Pr, Nd, Sm, Eu, Gd, Ho, Er) were almost linearly dependent on the no. of 4f electrons in the whole series of lanthanides. Also, the point, where the ratio of [LnL(H2O)n] : [LnL(H2O)n-1] is 1, shifts along the lanthanide series depending on the ligand denticity - the higher the ligand denticity, the farther the point of the equimolar ratio in the lanthanide series. The presented results are the 1st systematic exptl. study on the thermodn. description of the hydration equil. of Gd(III) compds.
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Graeppi, N.; Hugh Powell, D.; Laurenczy, G.; Zékány, L.; Merbach, A. E. Coordination Equilibria and Water Exchange Kinetics of Lanthanide(III) Propylenediaminetetraacetates and Other Magnetic Resonance Imaging Related Complexes. Inorg. Chim. Acta 1995, 235 (1–2), 311– 326, DOI: 10.1016/0020-1693(95)90073-F
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Coordination equilibria and water exchange kinetics of lanthanide(III) propylenediaminetetraacetates and other magnetic resonance imaging related complexes
Graeppi, Nicole; Powell, D. Hugh; Laurenczy, Gabor; Zekany, Laszlo; Merbach, Andre E.
Inorganica Chimica Acta (1995), 235 (1-2), 311-26CODEN: ICHAA3; ISSN:0020-1693. (Elsevier)
The UV-Vis absorption spectra of aq. solns. of Eu3+ complexes with the hexadentate polyaminocarboxylate ligands EDTA4-, CDTA4-, HDTA3- and PDTA4- were measured as a function of temp. and pressure in the frequency region corresponding to the 7F0→5D0 transition of Eu3+. The results can be explained in terms of equil. between nine-coordinate and eight-coordinate species where the eight-coordinate species contain one less inner sphere water mol. than the nine-coordinate species. The thermodn. parameters, including the reaction vol., for these equil. were detd. 17O NMR transverse relaxation rates and chem. shifts were measured for aq. solns. of the eight-coordinate complexes [Ln(PDTA)(H2O)2]- (Ln = Tb, Dy, Er, Tm, Yb) and [Er(EDTA)(H2O)2]- as a function of temp., pressure and magnetic field. The results were analyzed in terms of the water exchange kinetics on the complexes. The water exchange rate on [Ln(PDTA)(H2O)2]- decreases dramatically with decreasing ionic radius across the lanthanide series from kex298 = (2.4±0.1)×107 s-1 for Ln = Tb to kex298 = (2.8±0.3)×105 s-1 for Ln = Yb. The activation vols. show that this is accompanied by a change of exchange mechanism from associatively activated for Ln = Tb (ΔV # = -7.6±0.3 cm3 mol-1) to dissociatively activated for Ln = Yb (ΔV # = +7.4±0.8 cm3 mol-1). Water exchange on [Er(EDTA)(H2O)2]- (kex298 = (9.8±1.9)×106 s-1) is more than an order of magnitude faster than on [Er(PDTA)(H2O)2]- (kex298 = (5.6±0.5)×105 s-1). These kinetic results can be interpreted in terms of the equil. measured by UV-Vis spectrophotometry. The implications of these observations for the design of new MRI contrast agents are discussed.
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Balogh, E.; Mato-Iglesias, M.; Platas-Iglesias, C.; Tóth, É.; Djanashvili, K.; Peters, J. A.; de Blas, A.; Rodríguez-Blas, T. Pyridine- and Phosphonate-Containing Ligands for Stable Ln Complexation. Extremely Fast Water Exchange on the Gd^III Chelates. Inorg. Chem. 2006, 45 (21), 8719– 8728, DOI: 10.1021/ic0604157
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Pyridine- and Phosphonate-Containing Ligands for Stable Ln Complexation. Extremely Fast Water Exchange on the GdIII Chelates
Balogh, Edina; Mato-Iglesias, Marta; Platas-Iglesias, Carlos; Toth, Eva; Djanashvili, Kristina; Peters, Joop A.; de Blas, Andres; Rodriguez-Blas, Teresa
Inorganic Chemistry (2006), 45 (21), 8719-8728CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
Two novel ligands contg. pyridine units and phosphonate pendant arms, with ethane-1,2-diamine (L2) or cyclohexane-1,2-diamine (L3) backbones, have been synthesized for Ln complexation. The hydration nos. obtained from luminescence lifetime measurements in aq. solns. of the EuIII and TbIII complexes are q = 0.6 (EuL2), 0.7 (TbL2), 0.8 (EuL3), and 0.4 (TbL3). To further assess the hydration equil., we have performed a variable-temp. and -pressure UV-vis spectrophotometric study on the EuIII complexes. The reaction enthalpy, entropy, and vol. for the hydration equil. EuL ↔ EuL(H2O) were calcd. to be ΔH° = -(11.6 ± 2) kJ mol-1, ΔS° = -(34.2 ± 5) J mol-1 K-1, and KEu298 = 1.8 ± 0.3 for EuL2 and ΔH° = -(13.5 ± 1) kJ mol-1, ΔS° = -(41 ± 4) J mol-1 K-1, and KEu298 = 1.7 ± 0.3 for EuL3, resp. Variable-temp. 17O NMR and nuclear magnetic relaxation dispersion (NMRD) were measured for GdL2(H2O)q and GdL3(H2O)q systems. Given the presence of phosphonate groups in the ligand backbone, a second-sphere relaxation mechanism has been included for the anal. of the longitudinal 17O and 1H NMR relaxation rates. The water exchange rate on GdL2(H2O)q, kex298 = (7.0 ± 0.8) × 108 s-1, is extremely high and comparable to that on the GdIII aqua ion, while it is slightly reduced for GdL3(H2O)q, kex298 = (1.5 ± 0.1) × 108 s-1. This fast exchange can be rationalized in terms of a very flexible inner coordination sphere, which is slightly rigidified for L3 by the introduction of the cyclohexyl group on the amine backbone. The water exchange proceeds via a dissociative interchange mechanism, evidenced by the pos. activation vols. obtained from variable-pressure 17O NMR for both GdL2(H2O)q and GdL3(H2O)q (ΔV⧧ = +8.3 ± 1.0 and 8.7 ± 1.0 cm3 mol-1, resp.).
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Janicki, R.; Mondry, A. A New Approach to Determination of Hydration Equilibria Constants for the Case of [Er(EDTA)(H₂O)_n ]⁻ Complexes. Phys. Chem. Chem. Phys. 2014, 16 (48), 26823– 26831, DOI: 10.1039/C4CP04093G
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A new approach to determination of hydration equilibria constants for the case of [Er(EDTA)(H2O)n]- complexes
Janicki, Rafal; Mondry, Anna
Physical Chemistry Chemical Physics (2014), 16 (48), 26823-26831CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
Two anionic complexes [Er(EDTA)(H2O)2]- and [Er(EDTA)(H2O)3]- were obtained as the following compds.: [C(NH2)3]2[Er(EDTA)(H2O)2]ClO4·6H2O (1) and Na[Er(EDTA)(H2O)3]·5H2O (2), resp. The UV-visible-NIR absorption spectra of both monocrystals were measured at room temp. and at 4.2 K. The influence of coordination no. on intensities of the f-f transitions and the crystal field splitting of 2S+1LJ multiplets are discussed. The weighted sum of molar absorptivities of f-f transitions in the spectra of 1 and 2 was used to reproduce the absorption bands of the Er3+-EDTA complex in aq. soln. This approach allowed the authors to est. that the complex in soln. exists in 95% as the 8-coordinate [Er(EDTA)(H2O)2]- species and in 5% as the 9-coordinate [Er(EDTA)(H2O)3]- ones as well as to calc. the conditional hydration equil. const. (Kaqua) of the reaction: [Er(EDTA)(H2O)3]- ↔ [Er(EDTA)(H2O)2]- + H2O which is rather difficult to det. by using other methods. The Kaqua value is 19 ± 1.
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Zhang, J.; Dolg, M. Labile Capping Bonds in Lanthanide(III) Complexes: Shorter and Weaker. J. Phys. Chem. A 2015, 119 (4), 774– 780, DOI: 10.1021/jp511043c
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Labile Capping Bonds in Lanthanide(III) Complexes: Shorter and Weaker
Zhang, Jun; Dolg, Michael
Journal of Physical Chemistry A (2015), 119 (4), 774-780CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)
For a wide range of trivalent lanthanide ion coordination complexes of tricapped trigonal prism or monocapped square antiprism configurations, the bonds between the central lanthanide ions and the capping ligands are found to violate Badger's rule: they can get weaker as they get shorter. We demonstrate that this observation originates from the screening and repulsion effect of the prism ligands. Both effects enhance as the elec. field of the central ion or the softness of the prism ligands increases. Thus, for heavier lanthanides, despite the fact that the capping bond could be shorter, it is more efficient to be weakened by the prism ligands, being inherently labile. This concept of "labile capping bonds phenomenon" is then successfully used to interpret many problems in lanthanide(III) hydration, e.g., why the water exchange rate of a lanthanide(III) complex is much higher in a twisted square antiprism than in square antiprism configuration. Thus, the theory proposed in this paper offers new insights in understanding chem. problems.
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Quici, S.; Marzanni, G.; Forni, A.; Accorsi, G.; Barigelletti, F. New Lanthanide Complexes for Sensitized Visible and Near-IR Light Emission: Synthesis, ¹H NMR, and X-Ray Structural Investigation and Photophysical Properties. Inorg. Chem. 2004, 43 (4), 1294– 1301, DOI: 10.1021/ic035143b
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New Lanthanide Complexes for Sensitized Visible and Near-IR Light Emission: Synthesis, 1H NMR, and X-ray Structural Investigation and Photophysical Properties
Quici, Silvio; Marzanni, Giovanni; Forni, Alessandra; Accorsi, Gianluca; Barigelletti, Francesco
Inorganic Chemistry (2004), 43 (4), 1294-1301CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
The authors describe the syntheses, the 1H NMR studies in CD3OD and D2O as solvent, the x-ray characterization, and the luminescence properties in D2O soln. of the two complexes EuL and ErL (H3L = I), in which the phenanthroline unit which plays the role of light antenna for the sensitization process of the metal centered luminescence. In a previous report (Inorg. Chem. 2002, 41, 2777), for EuL there are no H2O mols. within the 1st coordination sphere. X-ray and 1H NMR results reported here are consistent with full satn. of the nine coordination sites within the EuL and ErL complexes. These studies provide important details regarding the conformations, square antiprism (SAP) and twisted square antiprism (TSAP), adopted in soln. by these complexes. The luminescence results are consistent with both an effective intersystem crossing (ISC) at the light absorbing phenanthroline unit (λexc = 278 nm) and an effective energy transfer (en) process from the phenanthroline donor to the cation acceptor (with unit or close to unit efficiency for both steps). In D2O solvent, the overall sensitization efficiency, φse, is 0.3 and 5 × 10-6, for EuL (main luminescence peaks at 585, 612, 699 nm) and ErL (luminescence peak at 1530 nm), resp. The photophys. properties of both complexes are discussed with ref. to their structural features as elucidated by the obtained 1H NMR and x-ray results.
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Storm Thomsen, M.; Andersen, H. O. B.; So̷rensen, T. J. Long Story Short: Donor Set Symmetry in [Eu(DOTA)(H₂O)]⁻ Crystals Determines the Electronic Structure. Dalton Trans. 2022, 51 (37), 14118– 14124, DOI: 10.1039/D2DT02172B
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Long story short: donor set symmetry in [Eu(DOTA)(H2O)]- crystals determines the electronic structure
Storm Thomsen, Maria; Andersen, Helene Obel Boech; Soerensen, Thomas Just
Dalton Transactions (2022), 51 (37), 14118-14124CODEN: DTARAF; ISSN:1477-9226. (Royal Society of Chemistry)
Lanthanide complexes of 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid DOTA have been studied in great detail due to their use as MRI contrast agents. Since the first report from Desreux in 1980, the Ln[DOTA]- complexes of gadolinium(III) in particular have been thoroughly investigated. The forms of the nine-coordinated [Ln(DOTA)(H2O)]- complexes are well known, and the ligand backbone has been used extensively to create functional MRI contrast agents, luminescent probes, and as a model system for studying the properties of lanthanide(III) ions. In soln., the photophys. properties have been mapped, but as the structures are not known, direct structure-property relationships have not been created. Here, the electronic properties of two Eu[DOTA] compds. (1 and 2) and a Eu[DOTA]-like compd. (3) were studied using single-crystal luminescence spectroscopy. The donor set in the three compds. is identical (4N 4O 1O), and using the symmetry deviation value σ-ideal it was shown that the coordination geometry is close to identical. Nevertheless, the electronic properties evaluated using the luminescence spectrum were found to differ significantly between the three compds. The magnitude of the crystal field splitting was found not to scale with the symmetry of the coordination geometry. It was concluded that the donor set dictates the splitting, yet the structure-property relationships governing the electronic properties of europium(III) ions still elude us.
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Howard, J. A. K.; Kenwright, A. M.; Moloney, J. M.; Parker, D.; Woods, M.; Howard, J. A. K.; Port, M.; Navet, M.; Rousseau, O. Structure and Dynamics of All of the Stereoisomers of Europium Complexes of Tetra(Carboxyethyl) Derivatives of Dota: Ring Inversion Is Decoupled from Cooperative Arm Rotation in the RRRR and RRRS Isomers. Chem. Commun. 1998, 13, 1381– 1382, DOI: 10.1039/a802847h
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83
Janicki, R.; Mondry, A. Structural and Thermodynamic Aspects of Hydration of Gd(iii) Systems. Dalton Trans. 2019, 48 (10), 3380– 3391, DOI: 10.1039/C8DT04869J
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83
Structural and thermodynamic aspects of hydration of Gd(III) systems
Janicki, Rafal; Mondry, Anna
Dalton Transactions (2019), 48 (10), 3380-3391CODEN: DTARAF; ISSN:1477-9226. (Royal Society of Chemistry)
X-ray crystal structures of Gd(III) and Lu(III) aqua ions as well as their complexes with polyaminopolycarboxylates (EDTA, CDTA, EGTA, DTPA, DOTA) were detd.: [Gd(H2O)9](CF3SO3)3, [Gd(H2O)8]Cl3·C10H20O5, [Lu(H2O)8]Cl3·C12H24O6·4H2O, [C(NH2)3][Gd(EDTA)(H2O)3], [C(NH2)3]2[Lu(EDTA)(H2O)2]ClO4·6H2O, [C(NH2)3][Lu(CDTA)(H2O)2]·6H2O, [C(NH2)3][Gd(EGTA)(H2O)]·2H2O, [C(NH2)2(N2H4)][Gd(HDTPA)(H2O)]·2H2O, Na[Gd(DOTA)(H2O)]·4H2O, and K2[Lu(DOTA)]Cl·4.6H2O. The weighted sums of UV absorption spectra of appropriate crystals were used to reproduce the spectra of the Gd(III) aq. solns. in the temp. range 276-363 K. In aq. soln. the Gd(III)-EGTA, Gd(III)-DTPA and Gd(III)-DOTA complexes exist as almost pure monohydrate [GdL(H2O)]n- species, while in the case of the Gd(III) aqua ion, Gd(III)-EDTA and Gd(III)-CDTA systems the equil. between variously hydrated species were found. The derived molar fractions of these species were used to det. the ΔG, ΔH and ΔS of hydration. These thermodn. functions may be derived not only from the spectra of the hypersensitive transitions, but from other f-f transitions as well. Next the ΔG, ΔH and ΔS values of hydration for the other Ln(III)-EDTA systems (Ln = Pr, Nd, Sm, Eu) were detd. The ΔG298 values of the dehydration reaction for Ln(III)-EDTA complexes (Ln = Pr, Nd, Sm, Eu, Gd, Ho, Er) were almost linearly dependent on the no. of 4f electrons in the whole series of lanthanides. Also, the point, where the ratio of [LnL(H2O)n] : [LnL(H2O)n-1] is 1, shifts along the lanthanide series depending on the ligand denticity - the higher the ligand denticity, the farther the point of the equimolar ratio in the lanthanide series. The presented results are the 1st systematic exptl. study on the thermodn. description of the hydration equil. of Gd(III) compds.
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Kriemen, E.; Holzapfel, M.; Ruf, E.; Rehbein, J.; Maison, W. Synthesis and Structural Analysis of 1,4,7,10-Tetraazacyclododecane-1,4,7,10-tetraazidoethylacetic Acid (DOTAZA) Complexes. Eur. J. Inorg. Chem. 2015, 2015 (32), 5368– 5378, DOI: 10.1002/ejic.201500789
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Synthesis and Structural Analysis of 1,4,7,10-Tetraazacyclododecane-1,4,7,10--tetraazidoethylacetic Acid (DOTAZA) Complexes
Kriemen, Ella; Holzapfel, Malte; Ruf, Erik; Rehbein, Julia; Maison, Wolfgang
European Journal of Inorganic Chemistry (2015), 2015 (32), 5368-5378CODEN: EJICFO; ISSN:1434-1948. (Wiley-VCH Verlag GmbH & Co. KGaA)
Herein, the authors present the synthesis and structural anal. of metal complexes of enantiomerically pure 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraazidoethylacetic acid (DOTAZA, I). DOTAZA is a new tunable analog of DOTA, a clin. approved chelator for various pharmaceutically relevant metal ions. The authors study the complexation chem. of DOTAZA and report the crystal structures of a no. of complexes with pharmaceutically relevant metal ions such as Gd3+ [magnetic resonance imaging (MRI)], Eu3+ (luminescence spectroscopy), Y3+ [positron emission tomog. (PET)], In3+ [single-photon-emission computed tomog. (SPECT)], and Na+. These structures provide useful information for imaging applications and demonstrate the potential of DOTAZA to form stable complexes. Owing to its clickable azide functionalities, it may be used for the development of tailored imaging reagents that retain the pos. complexation chem. of the parent compd. DOTA.
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Siega, P.; Wuerges, J.; Arena, F.; Gianolio, E.; Fedosov, S. N.; Dreos, R.; Geremia, S.; Aime, S.; Randaccio, L. Release of Toxic Gd³⁺ Ions to Tumour Cells by Vitamin B₁₂ Bioconjugates. Chem. – Eur. J. 2009, 15 (32), 7980– 7989, DOI: 10.1002/chem.200802680
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Release of Toxic Gd3+ Ions to Tumour Cells by Vitamin B12 Bioconjugates
Siega, Patrizia; Wuerges, Jochen; Arena, Francesca; Gianolio, Eliana; Fedosov, Sergey N.; Dreos, Renata; Geremia, Silvano; Aime, Silvio; Randaccio, Lucio
Chemistry - A European Journal (2009), 15 (32), 7980-7989, S7980/1-S7980/7CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)
Two probes consisting of vitamin B12 (CNCbl) conjugated to Gd chelates by esterification of the ribose 5'-OH moiety, Gd-DTPA-CNCbl (1; DTPA= diethylenetriamine-N,N,N',N'',N''-pentaacetic acid) and Gd-TTHA-CNCbl (2; TTHA= triethylenetetramine-N,N,N',N'',N''',N'''-hexaacetic acid), have been synthesized and characterized. The crystal structure of a dimeric form of 1, obtained by crystn. with an excess of GdCl3, has been detd. The kinetics of binding to and dissocn. from transcobalamin II show that 1 and 2 maintain high-affinity binding to the vitamin B12 transport protein. Complex 2 is very stable with respect to Gd3+ release owing to the satd. co-ordination of the Gd3+ ion by four amino and five carboxylate groups. Hydrolysis of the ester functionality occurs on the time scale of several hours. The lack of satn. and the possible involvement of the ester functionality in co-ordination result in lower stability of 1 towards hydrolysis and in a considerable release of Gd3+ in vitro. Gd3+ ions released from 1 are avidly taken up by the K562 tumor cells to an extent corresponding to approx. 1010 Gd3+ per cell. The internalization of toxic Gd3+ ions causes a marked decrease in cell viability as assessed by Trypan blue and WST-1 tests. On the contrary, the expts. with the more stable 2 did not show any significant cell internalization of Gd3+ ions and any influence on cell viability. The results point to new avenues of in situ generation of cytotoxic pathways based on the release of toxic Gd3+ ions by vitamin B12 bioconjugates.
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Campello, M. P. C.; Lacerda, S.; Santos, I. C.; Pereira, G. A.; Geraldes, C. F. G. C.; Kotek, J.; Hermann, P.; Vaněk, J.; Lubal, P.; Kubíček, V.; Tóth, É.; Santos, I. Lanthanide(III) Complexes of 4,10-Bis(Phosphonomethyl)-1,4,7,10-Tetraazacyclododecane-1,7-Diacetic Acid (Trans-H6do2a2p) in Solution and in the Solid State: Structural Studies Along the Series. Chem. – Eur. J. 2010, 16 (28), 8446– 8465, DOI: 10.1002/chem.201000320
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Lanthanide(III) Complexes of 4,10-Bis(phosphonomethyl)-1,4,7,10-tetraazacyclododecane-1,7-diacetic acid (trans-H6do2a2p) in Solution and in the Solid State: Structural Studies Along the Series
Campello, M. Paula C.; Lacerda, Sara; Santos, Isabel C.; Pereira, Giovannia A.; Geraldes, Carlos F. G. C.; Kotek, Jan; Hermann, Petr; Vanek, Jakub; Lubal, Premysl; Kubicek, Vojtech; Toth, Eva; Santos, Isabel
Chemistry - A European Journal (2010), 16 (28), 8446-8465, S8446/1-S8446/33CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)
Complexes of 4,10-bis(phosphonomethyl)-1,4,7,10-tetraazacyclododecane-1,7-diacetic acid (trans-H6do2a2p, H6L) with transition metal and lanthanide(III) ions were studied. The stability const. values of the divalent and trivalent metal-ion complexes are between the corresponding values of H4dota and H8dotp complexes, as a consequence of the ligand basicity. The solid-state structures of the ligand and of nine lanthanide(III) complexes were detd. by x-ray diffraction. All the complexes are present as twisted-square-antiprismatic isomers and their structures can be divided into two series. The first one involves nonacoordinated complexes of the large lanthanide(III) ions (Ce, Nd, Sm) with a coordinated H2O mol. For Sm, Eu, Tb, Dy, Er, Yb, the complexes are octacoordinated only by the ligand donor atoms and their coordination cages are more irregular. The formation kinetics and the acid-assisted dissocn. of several LnIII-H6L complexes were studied at different temps. and compared with analogous data for complexes of other dota-like ligands. The [Ce(L)(H2O)]3- complex is the most kinetically inert among complexes of the studied lanthanide(III) ions (Ce, Eu, Gd, Yb). Among mixed phosphonate-acetate dota analogs, kinetic inertness of the Ce(III) complexes is increased with a higher no. of phosphonate arms in the ligand, whereas the opposite is true for Eu(III) complexes. According to the 1H NMR spectroscopic pseudo-contact shifts for the Ce-Eu and Tb-Yb series, the soln. structures of the complexes reflect the structures of the [Ce(HL)(H2O)]2- and [Yb(HL)]2- anions, resp., found in the solid state. However, these soln. NMR spectroscopic studies showed that there is no unambiguous relation between 31P/1H lanthanide-induced shift (LIS) values and coordination of H2O in the complexes; the values rather express a relative position of the central ions between the N4 and O4 planes.
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Vojtíšek, P.; Cígler, P.; Kotek, J.; Rudovský, J.; Hermann, P.; Lukeš, I. Crystal Structures of Lanthanide(III) Complexes with Cyclen Derivative Bearing Three Acetate and One Methylphosphonate Pendants. Inorg. Chem. 2005, 44 (16), 5591– 5599, DOI: 10.1021/ic048190s
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Crystal Structures of Lanthanide(III) Complexes with Cyclen Derivative Bearing Three Acetate and One Methylphosphonate Pendants
Vojtisek, Pavel; Cigler, Petr; Kotek, Jan; Rudovsky, Jakub; Hermann, Petr; Lukes, Ivan
Inorganic Chemistry (2005), 44 (16), 5591-5599CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
Lanthanide(III) complexes formulated as M[Ln(Hdo3ap)]·xH2O (M = Li; Ln = Tb, Dy, Lu, Y and M = H; Ln = Er, Lu) with the monophosphonate analog of H4dota, 1,4,7,10-tetraazacyclododecane-1,4,7-triacetic-10-methylphosphonic acid (I; H5do3ap), were prepd. and studied using x-ray crystallog. All of the structures show that the (Hdo3ap)4- anion is octadentate coordinated to a lanthanide(III) ion similarly to the other H4dota-like ligands, i.e., forming O4 and N4 planes that are parallel and have mutual angle smaller than 3°. The lanthanide(III) ions lie between these planes, closer to the O4 base than to the N4 plane. All of the structures present the lanthanide(III) complexes in their twisted-square-antiprismatic (TSA) configuration. Twist angles of the pendants vary in the range between -24 and -30°, and for each complex, they lie in a very narrow region of 1°. The coordinated phosphonate oxygen is located slightly above (0.02-0.19 Å) the O3 plane formed with the coordinated acetates. The Dy, Y and Lu complexes are isostructural and can be formulated as [{Li(H2O)3}{M(Hdo3ap)}]·2H2O. These three complexes have a tetrahedral lithium coordinated only to one acetate O and 3 water mols. A water mol. is coordinated only in the terbium(III) and neodymium(III) complexes. The bond distance Tb-Ow is unusually long (2.678 Å). The O-Ln-O angles decrease from 140° [Nd(III)] to 121° [Lu(III)], thus confirming the increasing steric crowding around the water binding site. A comparison of a no. of structures of Ln(III) complexes with DOTA-like ligands shows that the TSA arrangement is flexible. However, the SA arrangement is rigid, and the derived structural parameters are almost identical for different ligands and lanthanide(III) ions.
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Bondi, A. Van Der Waals Volumes and Radii. J. Phys. Chem. 1964, 68 (3), 441– 451, DOI: 10.1021/j100785a001
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van der Waals volumes and radii
Bondi, A.
Journal of Physical Chemistry (1964), 68 (3), 441-51CODEN: JPCHAX; ISSN:0022-3654.
Intermol. van der Waals radii of the nonmetallic elements were assembled into a list of recommended values for vol. calcns. These values were arrived at by selecting from the most reliable x-ray diffraction data those which could be reconciled with crystal d. at 0°K. (to give reasonable packing d.), gas kinetic collision cross section, crit. d., and with liquid state properties. A qual. understanding of the nature of van der Waals radii is provided by correlation with the de Broglie wavelength of the outermost valence electron. Tentative values for the van der Waals radii of metallic elements in organometallic compds. are proposed. A list of increments for the vol. of mols. impenetrable to thermal collision, the so-called van der Waals vol., and of the corresponding increments in area per mol. is given.
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Rowland, R. S.; Taylor, R. Intermolecular Nonbonded Contact Distances in Organic Crystal Structures: Comparison with Distances Expected from van Der Waals Radii. J. Phys. Chem. 1996, 100 (18), 7384– 7391, DOI: 10.1021/jp953141+
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Intermolecular Nonbonded Contact Distances in Organic Crystal Structures: Comparison with Distances Expected from van der Waals Radii
Rowland, R. Scott; Taylor, Robin
Journal of Physical Chemistry (1996), 100 (18), 7384-91CODEN: JPCHAX; ISSN:0022-3654. (American Chemical Society)
The conclusions derived from systematic analyses of intermol. contact distances in org. crystals may be affected by the values assumed for van der Waals radii. The most widely used tabulations of van der Waals radii date back 30 yr or more. Also, many of the tabulated values were chosen to reproduce vols., not contact distances, in crystals. Literally millions of nonbonded contact distances were characterized by crystallog. since the tabulations were compiled. A study has therefore been performed to establish the degree of consistency between these accumulated crystallog. data and the van der Waals radii of the common nonmetallic elements, as compiled by Pauling and Bondi. For halogens and S, the results show a remarkable agreement between obsd. contact distances and the Bondi radii. Agreement is slightly less good for C, N, and O, but discrepancies are still only ∼0.05 Å. However, there is a significant difference for H, where the Bondi value of 1.2 Å is probably too high by ∼0.1 Å.
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Fernández-Fernández, M. D. C.; Bastida, R.; Macías, A.; Pérez-Lourido, P.; Platas-Iglesias, C.; Valencia, L. Lanthanide(III) Complexes with a Tetrapyridine Pendant-Armed Macrocyclic Ligand: 1H NMR Structural Determination in Solution, X-Ray Diffraction, and Density-Functional Theory Calculations. Inorg. Chem. 2006, 45 (11), 4484– 4496, DOI: 10.1021/ic0603508
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Lanthanide(III) Complexes with a Tetrapyridine Pendant-Armed Macrocyclic Ligand: 1H NMR Structural Determination in Solution, X-ray Diffraction, and Density-Functional Theory Calculations
Fernandez-Fernandez, M. del C.; Bastida, R.; Macias, A.; Perez-Lourido, P.; Platas-Iglesias, C.; Valencia, L.
Inorganic Chemistry (2006), 45 (11), 4484-4496CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
Complexes between the tetrapyridyl pendant-armed macrocyclic ligand (L) and the trivalent lanthanide ions were synthesized, and structural studies were made both in the solid state and in aq. soln. The crystal structures of the La, Ce, Pr, Gd, Tb, Er, and Tm complexes were detd. by single-crystal x-ray crystallog. In the solid state, all the cation complexes show a 10-coordinated geometry close to a distorted bicapped antiprism, with the pyridine pendants situated alternatively above and below the main plane of the macrocycle. The conformations of the two five-membered chelate rings present in the complexes change along the lanthanide series. The La(III) and Ce(III) complexes show a λδ (or δλ) conformation, while the complexes of the heavier lanthanide ions present λλ (or δδ) conformation. The cationic [Ln(L)]3+ complexes (Ln = La, Pr, Eu, Tb, and Tm) were also characterized by theor. calcns. at the d.-functional theory (DFT) B3LYP level. The theor. calcns. predict a stabilization of the λλ (or δδ) conformation on decreasing the ionic radius of the Ln(III) ion, in agreement with the exptl. evidence. The soln. structures show a good agreement with the calcd. ones, as demonstrated by paramagnetic NMR measurements (lanthanide induced shifts and relaxation rate enhancements). The 1H NMR spectra indicate an effective D2 symmetry of the complexes in D2O soln. The 1H lanthanide induced shifts (LIS) obsd. for the Ce(III), Tm(III), and Yb(III) complexes can be fit to a theor. model assuming that dipolar contributions are dominant for all protons. The resulting calcd. values are consistent with highly rhombic magnetic susceptibility tensors with the magnetic axes being coincident with the symmetry axes of the mol. In contrast with the solid-state structure, the anal. of the LIS data indicates that the Ce(III) complexes present a λλ (or δδ) conformation in soln.
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Castro, G.; Regueiro-Figueroa, M.; Esteban-Gómez, D.; Bastida, R.; Macías, A.; Pérez-Lourido, P.; Platas-Iglesias, C.; Valencia, L. Exceptionally Inert Lanthanide(III) PARACEST MRI Contrast Agents Based on an 18-Membered Macrocyclic Platform. Chem. – Eur. J. 2015, 21 (51), 18662– 18670, DOI: 10.1002/chem.201502937
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Exceptionally Inert Lanthanide(III) PARACEST MRI Contrast Agents Based on an 18-Membered Macrocyclic Platform
Castro, Goretti; Regueiro-Figueroa, Martin; Esteban-Gomez, David; Bastida, Rufina; Macias, Alejandro; Perez-Lourido, Paulo; Platas-Iglesias, Carlos; Valencia, Laura
Chemistry - A European Journal (2015), 21 (51), 18662-18670CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)
We report a macrocyclic ligand based on a 3,6,10,13-tetraaza-1,8(2,6)-dipyridinacyclotetradecaphane platform contg. four hydroxyethyl pendant arms (L1) that forms extraordinary inert complexes with Ln3+ ions. The [EuL1]3+ complex does not undergo dissocn. in 1 M HCl over a period of months at room temp. Furthermore, high concns. of phosphate and Zn2+ ions at room temp. do not provoke metal-complex dissocn. The X-ray crystal structures of six Ln3+ complexes reveal ten coordination of the ligand to the metal ions through the six nitrogen atoms of the macrocycle and the four oxygen atoms of the hydroxyethyl pendant arms. The anal. of the Yb3+- and Pr3+-induced paramagnetic 1H NMR shifts show that the solid-state structures are retained in aq. soln. The intensity of the 1H NMR signal of bulk water can be modulated by satn. of the signals of the hydroxy protons of Pr3+, Eu3+, and Yb3+ complexes following chem.-exchange satn. transfer (CEST). The ability of these complexes to provide large CEST effects at 25 and 37 °C and pH 7.4 was confirmed by using CEST magnetic resonance imaging expts.
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Xing, Y.; Jindal, A. K.; Regueiro-Figueroa, M.; Le Fur, M.; Kervarec, N.; Zhao, P.; Kovacs, Z.; Valencia, L.; Pérez-Lourido, P.; Tripier, R.; Esteban-Gómez, D.; Platas-Iglesias, C.; Sherry, A. D. The Relationship between NMR Chemical Shifts of Thermally Polarized and Hyperpolarized 89Y Complexes and Their Solution Structures. Chem. – Eur. J. 2016, 22 (46), 16657– 16667, DOI: 10.1002/chem.201602901
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The Relationship between NMR Chemical Shifts of Thermally Polarized and Hyperpolarized 89Y Complexes and Their Solution Structures
Xing, Yixun; Jindal, Ashish K.; Regueiro-Figueroa, Martin; Le Fur, Mariane; Kervarec, Nelly; Zhao, Piyu; Kovacs, Zoltan; Valencia, Laura; Perez-Lourido, Paulo; Tripier, Raphael; Esteban-Gomez, David; Platas-Iglesias, Carlos; Sherry, A. Dean
Chemistry - A European Journal (2016), 22 (46), 16657-16667CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)
Recently developed dynamic nuclear polarization (DNP) technol. offers the potential of increasing the NMR sensitivity of even rare nuclei for biol. imaging applications. Hyperpolarized 89Y is an ideal candidate because of its narrow NMR linewidth, favorable spin quantum no. (I=1/2), and long longitudinal relaxation times (T1). Strong NMR signals were detected in hyperpolarized 89Y samples of a variety of yttrium complexes. A dataset of 89Y NMR data composed of 23 complexes with polyaminocarboxylate ligands was obtained using hyperpolarized 89Y measurements or 1H,89Y-HMQC spectroscopy. These data were used to derive an empirical equation that describes the correlation between the 89Y chem. shift and the chem. structure of the complexes. This empirical correlation serves as a guide for the design of 89Y sensors. Relativistic (DKH2) DFT calcns. were found to predict the exptl. 89Y chem. shifts to a rather good accuracy.
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Gambino, T.; Valencia, L.; Pérez-Lourido, P.; Esteban-Gómez, D.; Zaiss, M.; Platas-Iglesias, C.; Angelovski, G. Inert Macrocyclic Eu ³⁺ Complex with Affirmative paraCEST Features. Inorg. Chem. Front. 2020, 7 (12), 2274– 2286, DOI: 10.1039/C9QI01612K
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Inert macrocyclic Eu3+ complex with affirmative paraCEST features
Gambino, Tanja; Valencia, Laura; Perez-Lourido, Paulo; Esteban-Gomez, David; Zaiss, Moritz; Platas-Iglesias, Carlos; Angelovski, Goran
Inorganic Chemistry Frontiers (2020), 7 (12), 2274-2286CODEN: ICFNAW; ISSN:2052-1553. (Royal Society of Chemistry)
We report on a macrocyclic platform based on an 18-membered macrocycle that forms kinetically highly inert paramagnetic complexes and possesses an excellent outlook for the development of bioresponsive paraCEST (paramagnetic chem. exchange satn. transfer) contrast agents. The investigated europium(III) chelate is non-hydrated and contains four amide groups, each possessing two paramagnetically shifted proton resonances distant from bulk water. The X-ray crystal structure and soln. studies indicate that the metal ion is ten-coordinated, being directly bound to the six N atoms of the macrocycle and the four amide O atoms of the pendant arms. The complex presents an excellent inertness with respect to dissocn., being stable under a variety of harsh conditions, including highly acidic and basic media or elevated temps. The amide protons are in slow-to-intermediate exchange with bulk water, which gives rise to the generation of a strong CEST effect at low probe concn. and satn. powers (~ 25% at 5 mM, B1 = 5 μT, 37 °C). We demonstrate the potential of this platform for mapping pH in its microenvironment and foresee potential for the development of diverse paraCEST probes and sensors.
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Harriswangler, C.; Caneda-Martínez, L.; Rousseaux, O.; Esteban-Gómez, D.; Fougère, O.; Pujales-Paradela, R.; Valencia, L.; Fernández, M. I.; Lepareur, N.; Platas-Iglesias, C. Versatile Macrocyclic Platform for the Complexation of [natY/90Y]Yttrium and Lanthanide Ions. Inorg. Chem. 2022, 61 (16), 6209– 6222, DOI: 10.1021/acs.inorgchem.2c00378
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Versatile Macrocyclic Platform for the Complexation of [natY/90Y]Yttrium and Lanthanide Ions
Harriswangler, Charlene; Caneda-Martinez, Laura; Rousseaux, Olivier; Esteban-Gomez, David; Fougere, Olivier; Pujales-Paradela, Rosa; Valencia, Laura; Fernandez, M. Isabel; Lepareur, Nicolas; Platas-Iglesias, Carlos
Inorganic Chemistry (2022), 61 (16), 6209-6222CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
We report a macrocyclic ligand (H3L6) based on a 3,6,10,13-tetraaza-1,8(2,6)-dipyridinacyclotetradecaphane platform contg. three acetate pendant arms and a benzyl group attached to the fourth nitrogen atom of the macrocycle. The X-ray structures of the YL6 and TbL6 complexes reveal nine coordination of the ligand to the metal ions through the six nitrogen atoms of the macrocycle and three oxygen atoms of the carboxylate pendants. A combination of NMR spectroscopic studies (1H, 13C, and 89Y) and DFT calcns. indicated that the structure of the YL6 complex in the solid state is maintained in an aq. soln. The detailed study of the emission spectra of the EuL6 and TbL6 complexes revealed Ln3+-centered emission with quantum yields of 7.0 and 60%, resp. Emission lifetime measurements indicate that the ligand offers good protection of the metal ions from surrounding water mols., preventing the coordination of water mols. The YL6 complex is remarkably inert with respect to complex dissocn., with a lifetime of 1.7 h in 1 M HCl. On the other hand, complex formation is fast (~ 1 min at pH 5.4, 2 × 10-5 M). Studies using the 90Y-nuclide confirmed fast radiolabeling since [90Y]YL6 is nearly quant. formed (radiochem. yield (RCY) > 95) in a short time over a broad range of pH values from ca. 2.4 to 9.0. Challenging expts. in the presence of excess EDTA and in human serum revealed good stability of the [90Y]YL6 complex. All of these expts. combined suggest the potential application of H3L6 derivs. as Y-based radiopharmaceuticals.
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Inorganic Chemistry

Cite this: Inorg. Chem. 2023, 62, 41, 17030–17040

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https://doi.org/10.1021/acs.inorgchem.3c03126

Published October 2, 2023

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Abstract
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Chart 1
Chart 1. Structures of Ligands Discussed in the Present Work
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Figure 1
Figure 1. Coordination numbers observed in the X-ray structures of the Ln(III) DOTA^4– and DTPA^5– derivatives.
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Figure 2
Figure 2. Histograms showing the bond distances involving the Ln(III) ion, carboxylate-O donor atoms, and amine N atoms. Top panel: Gd(III) complexes with CN 9 (347 Gd–O_C and 450 Gd–N_A distances); central panel: Yb(III) complexes with CN 9 (63 Yb–O_C and 155 Yb–N_A distances). Low panel: Yb(III) complexes with CN 8 (30 Yb–O_C and 89 Yb–N_A distances).
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Figure 3
Figure 3. Electron densities (ρ) calculated along the Ln-donor paths for different lanthanide complexes with the metal ion placed at the origin. The position of the donor atom corresponds to the maximum of ρ around 2.5 Å; CPs indicated with crosses: (a) [Gd(DTPA)(H₂O)]^2–, CSD code FEPREY; (b) Ln–O_C bonds in [Ln(DTPA)(H₂O)]^2–, Ln = Nd, Yb, CSD codes CUVZOI and KOLGIB); (c) La–O_AM bonds in [La(DOTAM)]³⁺ (CN 8) and [La(DOTAM)(CF₃SO₃)(EtOH)]³⁺ (CN 10), CSD codes PIBGOW and PIRSEO; (d) Eu–O_Phos bonds in [Eu^III(DOTP)]^5– and [Eu^II(DOTP)]^6–, CSD codes AXAMET and ONETEJ. Electron densities were calculated with Multiwfn. (68)
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Figure 4
Figure 4. Plot according to eq 1 of bond distances (d_Ln–D) involving amine N atoms versus crystal radii.
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Figure 5
Figure 5. Plots according to eq 1 of bond distances (d_Ln–D) involving chloride (green circles) and fluoride (blue circles). The orange circles correspond to distances erroneously assigned to Ln–Cl bonds instead of Ln–F bonds (see test).
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Figure 6
Figure 6. Structure of the [Eu(L^py)(H₂O)]³⁺ cation present in the crystals of [Eu(L^py)(H₂O)](PF₆)₃·2H₂O.
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Figure 7
Figure 7. Histograms showing the differences between experimental and calculated bond distances involving the Ln(III) ion and carboxylate O donor atoms and amine N atoms (Δd = d^exp – d^cal, with d^cal = r_D + CR_Ln).
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Figure 8
Figure 8. Histograms showing the differences between experimental and calculated bond distances involving the rare-earth ion and different donor atoms (Δd = d^cal – d^exp, with d^cal = r_D + CR_Ln). Histograms were constructed from data obtained for all rare-earth cations. The numbers within parentheses indicate the number of data points.
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References
This article references 94 other publications.
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  Parker, David; Dickins, Rachel S.; Puschmann, Horst; Crossland, Clare; Howard, Judith A. K.
  Chemical Reviews (Washington, DC, United States) (2002), 102 (6), 1977-2010CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
  A review. Lanthanide (Ln) coordination complexes are reviewed with emphasis on structural anal. of 9-coordinate aqua-Ln species, chirality in aq. soln., exchange dynamics, excited-state chem. and magnetic resonance applications.
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2. 2
  Marcus, Y. Thermodynamics of Solvation of Ions. J. Chem. Soc., Faraday Trans. 1991, 87, 2995– 2999, DOI: 10.1039/FT9918702995
  2
  Thermodynamics of solvation of ions. 5. Gibbs free energy of hydration at 298.15 K
  Marcus, Yizhak
  Journal of the Chemical Society, Faraday Transactions (1991), 87 (18), 2995-9CODEN: JCFTEV; ISSN:0956-5000.
  The std. molar free energies of hydration, ΔhvdG0, of 109 (mainly inorg.) ions ranging in their charges from -3 to +4 were compiled and interpreted in terms of a model used previously for other thermodn. quantities of hydration. The main contributions to ΔhydG0 are the electrostatic effects, resulting in solvent immobilization, electrostriction, and dielec. satn. in a hydration shell of specified thickness, and further such effects on the water that surrounds this shell. Other effects contribute to ΔhydG0 to a minor extent only.
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3. 3
  Regueiro-Figueroa, M.; Esteban-Gómez, D.; de Blas, A.; Rodríguez-Blas, T.; Platas-Iglesias, C. Understanding Stability Trends along the Lanthanide Series. Chem. – Eur. J. 2014, 20 (14), 3974– 3981, DOI: 10.1002/chem.201304469
  3
  Understanding Stability Trends along the Lanthanide Series
  Regueiro-Figueroa, Martin; Esteban-Gomez, David; de Blas, Andres; Rodriguez-Blas, Teresa; Platas-Iglesias, Carlos
  Chemistry - A European Journal (2014), 20 (14), 3974-3981CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)
  The stability trends across the lanthanide series of complexes with the polyaminocarboxylate ligands TETA4- (H4TETA = 2,2',2'',2'''-(1,4,8,11-tetraazacyclotetradecane-1,4,8,11-tetrayl)tetraacetic acid), BCAED4- (H4BCAED = 2,2',2'',2'''-{[(1,4-diazepane-1,4-diyl)bis(ethane-2,1-diyl)]bis(azanetriyl)}tetraacetic acid), and BP18C62- (H2BP18C6 = 6,6'-[(1,4,10,13-tetraoxa-7,16-diazacyclooctadecane-7,16-diyl)bis(methylene)]dipicolinic acid) were investigated using DFT calcns. Geometry optimizations performed at the TPSSh/6-31G(d,p) level, and using a 46 + 4fn ECP for lanthanides, provide bond lengths of the metal coordination environments in good agreement with the exptl. values obsd. in the X-ray structures. The contractions of the Ln3+ coordination spheres follow quadratic trends, as obsd. previously for different isostructural series of complexes. We show here that the parameters obtained from the quant. anal. of these data can be used to rationalize the obsd. stability trends across the 4f period. The stability trends along the lanthanide series were also evaluated by calcg. the free energy for the reaction [La(L)]n+/-(sol) + Ln3+(sol)→[Ln(L)]n+/-(sol) + La3+(sol). A parameterization of the Ln3+ radii was performed by minimizing the differences between exptl. and calcd. std. hydration free energies. The calcd. stability trends are in good agreement with the exptl. stability consts., which increase markedly across the series for BCAED4- complexes, increase smoothly for the TETA4- analogs, and decrease in the case of BP18C62- complexes. The resulting stability trend is the result of a subtle balance between the increased binding energies of the ligand across the lanthanide series, which contribute to an increasing complex stability, and the increase in the abs. values of hydration energies along the 4f period.
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4. 4
  Pearson, R. Hard and Soft Acids and Bases. J. Am. Chem. Soc. 1963, 85, 3533– 3539, DOI: 10.1021/ja00905a001
  4
  Hard and soft acids and bases
  Pearson, Ralph G.
  Journal of the American Chemical Society (1963), 85 (22), 3533-9CODEN: JACSAT; ISSN:0002-7863.
  A number of Lewis acids of diverse types are classified as (a) or (b) following the criterion of Ahrland, et al. (CA 53, 960c). Other, auxiliary criteria are proposed. Class (a) acids prefer to bind to "hard" or nonpolarizable bases. Class (b) acids prefer to bind to "soft" or polarizable bases. Since class (a) acids are themselves "hard" and since class (b) acids are "soft" a simple, useful rule is proposed: hard acids bind strongly to hard bases and soft acids bind strongly to soft bases. The explanations for such behavior include: (1) various degrees of ionic and covalent σ-bonding; (2) π-bonding; (3) electron correlation phenomena; (4) solvation effects.
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5. 5
  Cotton, S. A. Establishing Coordination Numbers for the Lanthanides in Simple Complexes. C. R. Chim. 2005, 8 (2), 129– 145, DOI: 10.1016/j.crci.2004.07.002
  5
  Establishing coordination numbers for the lanthanides in simple complexes
  Cotton, Simon A.
  Comptes Rendus Chimie (2005), 8 (2), 129-145CODEN: CRCOCR; ISSN:1631-0748. (Editions Scientifiques et Medicales Elsevier)
  A review. This article reviews the development of the understanding of the coordination no. in lanthanide complexes, showing how it was realized in the 1960s that lanthanide complexes frequently had much higher coordination nos. than 6, and how it subsequently became possible for chemists to synthesize compds. with coordination nos. as low as 2, 3 and 4. Subsequent sections examine how coordination of solvent can cause uncertainties in coordination nos.; the detn. of the coordination no. of the aqua ions and in hydrated salts; variations (or not) in coordination no. across the lanthanide series; the effect of counterion upon coordination no.; and agostic interactions and interactions with distant atoms (when is a bond not a bond).
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6. 6
  Bünzli, J.-C. G. Review: Lanthanide Coordination Chemistry: From Old Concepts to Coordination Polymers. J. Coord. Chem. 2014, 67 (23–24), 3706– 3733, DOI: 10.1080/00958972.2014.957201
  There is no corresponding record for this reference.
7. 7
  Moeller, T.; Thompson, L. C. Observations on the Rare Earths--LXXV. The Stabilities of Diethylenetriaminepentaacetic Acid Chelates. J. Inorg. Nucl. Chem. 1962, 24, 499– 510, DOI: 10.1016/0022-1902(62)80236-X
  7
  The rare earths. LXXV. The stabilities of diethylenetriaminepentaacetic acid chelates
  Moeller, T.; Thompson, L. C.
  Journal of Inorganic and Nuclear Chemistry (1962), 24 (), 499-510CODEN: JINCAO; ISSN:0022-1902.
  cf. CA 56, 6727b, 11002h. The interaction between diethylenetriaminepentaacetic acid (H5DTPA or H5Z) and rare earth metal ions (Ln+++) was investigated. The acid formation consts. of the H chelates (LnHZ-) and the formation consts. of the normal chelates (LnZ--) were obtained at 10, 20, and 30°, and an ionic strength of 0.1 (KNO3), the former by a titration technique and the latter by a Hg indicator electrode technique. δH° and δS° were detd. Although errors in these functions are substantial, the functions were related to observed trends in stability. The dissocn. consts. for the last 3 protons of diethylenetriaminepentaacetic acid were measured as a function of temp. at ionic strength 0.1 (KNO3) and converted to thermodynamic functions by least squares analysis. These functions were compared with corresponding values for related chelating agents.
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8. 8
  Loncin, M. F.; Desreux, J. F.; Merciny, E. Coordination of Lanthanides by Two Polyamino Polycarboxylic Macrocycles: Formation of Highly Stable Lanthanide Complexes. Inorg. Chem. 1986, 25 (15), 2646– 2648, DOI: 10.1021/ic00235a031
  8
  Coordination of lanthanides by two polyamino polycarboxylic macrocycles: formation of highly stable lanthanide complexes
  Loncin, M. F.; Desreux, J. F.; Merciny, E.
  Inorganic Chemistry (1986), 25 (15), 2646-8CODEN: INOCAJ; ISSN:0020-1669.
  The formation consts. of a few lanthanide complexes with DOTA (1,4,7,10-tetraazacyclododecane-N,N',N'',N'''-tetraacetic acid) and TETA (1,4,8,11-tetraazacyclotetradecane-N,N',N'',N'''-tetraacetic acid) were measured by potentiometric and competition methods. The ligand DOTA forms the most stable lanthanide chelates known so far (log KML = 28.2-29.2) while the stability of the TETA compds. at 80° (log KML = 14.5-16.5) is comparable to the stability of the EDTA complexes. A competition method with the C2O42- anion as a probe had to be used for detg. the formation consts. of the DOTA lanthanide chelates because of the high stability of these compds. The relative stability of the DOTA and TETA complexes is accounted for by steric factors with ref. to known soln.- and solid-state structures.
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9. 9
  Clough, T. J.; Jiang, L.; Wong, K.-L.; Long, N. J. Ligand Design Strategies to Increase Stability of Gadolinium-Based Magnetic Resonance Imaging Contrast Agents. Nat. Commun. 2019, 10 (1), 1420, DOI: 10.1038/s41467-019-09342-3
  9
  Ligand design strategies to increase stability of gadolinium-based magnetic resonance imaging contrast agents
  Clough Thomas J; Jiang Lijun; Long Nicholas J; Jiang Lijun; Wong Ka-Leung
  Nature communications (2019), 10 (1), 1420 ISSN:.
  Gadolinium(III) complexes have been widely utilised as magnetic resonance imaging (MRI) contrast agents for decades. In recent years however, concerns have developed about their toxicity, believed to derive from demetallation of the complexes in vivo, and the relatively large quantities of compound required for a successful scan. Recent efforts have sought to enhance the relaxivity of trivalent gadolinium complexes without sacrificing their stability. This review aims to examine the strategic design of ligands synthesised for this purpose, provide an overview of recent successes in gadolinium-based contrast agent development and assess the requirements for clinical translation.
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10. 10
  Uzal-Varela, R.; Rodríguez-Rodríguez, A.; Wang, H.; Esteban-Gómez, D.; Brandariz, I.; Gale, E. M.; Caravan, P.; Platas-Iglesias, C. Prediction of Gd(III) Complex Thermodynamic Stability. Coord. Chem. Rev. 2022, 467, 214606 DOI: 10.1016/j.ccr.2022.214606
  10
  Prediction of Gd(III) complex thermodynamic stability
  Uzal-Varela, Rocio; Rodriguez-Rodriguez, Aurora; Wang, Huan; Esteban-Gomez, David; Brandariz, Isabel; Gale, Eric M.; Caravan, Peter; Platas-Iglesias, Carlos
  Coordination Chemistry Reviews (2022), 467 (), 214606CODEN: CCHRAM; ISSN:0010-8545. (Elsevier B.V.)
  Gadolinium(III) complexes are widely employed as contrast agents in diagnostic magnetic resonance imaging, and the development of new contrast agents remains a highly active field. A key requisite for contrast agents is high thermodn. stability of the complex to ensure that the Gd(III) ion is not released in the body. Here we utilized published stability consts. spanning 20 orders of magnitude to develop empirical expressions based on structural descriptors to predict the Gd(III)-ligand formation const. as well as pGd at pH 7.4. We then tested the predictive power of these expressions and found excellent agreement with a mean deviation of 1.0 log K units. The magnitudes of the structural descriptors are useful for guiding ligand design for Gd(III), and the empirical stability const. expressions can be used to screen potential ligands. This methodol. is readily extended to other aq. metal ion systems.
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11. 11
  Wahsner, J.; Gale, E. M.; Rodríguez-Rodríguez, A.; Caravan, P. Chemistry of MRI Contrast Agents: Current Challenges and New Frontiers. Chem. Rev. 2019, 119 (2), 957– 1057, DOI: 10.1021/acs.chemrev.8b00363
  11
  Chemistry of MRI Contrast Agents: Current Challenges and New Frontiers
  Wahsner, Jessica; Gale, Eric M.; Rodriguez-Rodriguez, Aurora; Caravan, Peter
  Chemical Reviews (Washington, DC, United States) (2019), 119 (2), 957-1057CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
  A review. Tens of millions of contrast-enhanced magnetic resonance imaging (MRI) exams are performed annually around the world. The contrast agents, which improve diagnostic accuracy, are almost exclusively small, hydrophilic gadolinium(III) based chelates. In recent years concerns have arisen surrounding the long-term safety of these compds., and this has spurred research into alternatives. There has also been a push to develop new molecularly targeted contrast agents or agents that can sense pathol. changes in the local environment. This comprehensive review describes the state of the art of clin. approved contrast agents, their mechanism of action, and factors influencing their safety. From there we describe different mechanisms of generating MR image contrast such as relaxation, chem. exchange satn. transfer, and direct detection and the types of mols. that are effective for these purposes. Next we describe efforts to make safer contrast agents either by increasing relaxivity, increasing resistance to metal ion release, or by moving to gadolinium(III)-free alternatives. Finally we survey approaches to make contrast agents more specific for pathol. either by direct biochem. targeting or by the design of responsive or activatable contrast agents.
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12. 12
  Kostelnik, T. I.; Orvig, C. Radioactive Main Group and Rare Earth Metals for Imaging and Therapy. Chem. Rev. 2019, 119 (2), 902– 956, DOI: 10.1021/acs.chemrev.8b00294
  12
  Radioactive Main Group and Rare Earth Metals for Imaging and Therapy
  Kostelnik, Thomas I.; Orvig, Chris
  Chemical Reviews (Washington, DC, United States) (2019), 119 (2), 902-956CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
  Radiometals possess an exceptional breadth of decay properties and have been applied to medicine with great success for several decades. The majority of current clin. use involves diagnostic procedures, which use either positron-emission tomog. (PET) or single-photon imaging to detect anat. abnormalities that are difficult to visualize using conventional imaging techniques (e.g., MRI and X-ray). The potential of therapeutic radiometals has more recently been realized and relies on ionizing radiation to induce irreversible DNA damage, resulting in cell death. In both cases, radiopharmaceutical development has been largely geared toward the field of oncol.; thus, selective tumor targeting is often essential for efficacious drug use. To this end, the rational design of four-component radiopharmaceuticals has become popularized. This Review introduces fundamental concepts of drug design and applications, with particular emphasis on bifunctional chelators (BFCs), which ensure secure consolidation of the radiometal and targeting vector and are integral for optimal drug performance. Also presented are detailed accounts of prodn., chelation chem., and biol. use of selected main group and rare earth radiometals.
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13. 13
  Bünzli, J.-C. G. Lanthanide Luminescence for Biomedical Analyses and Imaging. Chem. Rev. 2010, 110 (5), 2729– 2755, DOI: 10.1021/cr900362e
  13
  Lanthanide Luminescence for Biomedical Analyses and Imaging
  Bunzli, Jean-Claude G.
  Chemical Reviews (Washington, DC, United States) (2010), 110 (5), 2729-2755CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
  A review. This review addresses the problematics of lanthanide luminescent bioprobes (LLB) from the standpoint of their photophys. and biochem. properties; a broad overview of the various applications in which LLBs have been applied is given.
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14. 14
  Bünzli, J.-C. G. On the Design of Highly Luminescent Lanthanide Complexes. Coord. Chem. Rev. 2015, 293–294, 19– 47, DOI: 10.1016/j.ccr.2014.10.013
  14
  On the design of highly luminescent lanthanide complexes
  Bunzli, Jean-Claude G.
  Coordination Chemistry Reviews (2015), 293-294 (), 19-47CODEN: CCHRAM; ISSN:0010-8545. (Elsevier B.V.)
  Presently, phosphors and luminescent materials for lighting, telecommunications, displays, security inks and marking, as well as for probes in biosciences represent one third of the total value of the lanthanides used worldwide. If optical glasses and laser materials are added, this figure is close to 40%, explaining the large interest that the scientific community is devoting to such materials. The present review focuses on the design of highly luminescent lanthanide complexes and discusses all aspects needing optimization. Ref. is made to the mastering of the various energy migration processes in luminescence sensitization by org. ligands, to minimizing non-radiative deactivation mechanisms, as well as to other parameters such as the radiative lifetime, the refractive index, and the benefit of inserting luminescent complexes into inorg.-hybrid structures. Comparative tables list the most luminescent complexes emitting in the visible and near-IR ranges and the best chromophores are pointed out.
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15. 15
  Nonat, A. M.; Charbonnière, L. J. Upconversion of Light with Molecular and Supramolecular Lanthanide Complexes. Coord. Chem. Rev. 2020, 409, 213192 DOI: 10.1016/j.ccr.2020.213192
  15
  Upconversion of light with molecular and supramolecular lanthanide complexes
  Nonat, Aline M.; Charbonniere, Loic J.
  Coordination Chemistry Reviews (2020), 409 (), 213192CODEN: CCHRAM; ISSN:0010-8545. (Elsevier B.V.)
  A review. Upconversion (UC) is the process by which the energy of multiple photons is absorbed by a compd. and restored in the form of a photon of higher energy than the incident light, resulting in an anti-Stokes process. Although studied theor. since the middle of the last century and exptl. obsd. in the 1960's, the process was up to recently mainly restricted to solid state devices and ultimately to nanoparticles at the end of the century. At the same period, different researches were directed towards the possibility to observe UC at the mol. level and it is only recently that the phenomenon could be obsd. in discrete mol. entities in soln. with still very few examples. This review aims at explaining the difficulties encountered at the mol. level compared to the solid state and summarizes the results reported to date on UC at the mol. scale.
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16. 16
  Aboshyan-Sorgho, L.; Cantuel, M.; Petoud, S.; Hauser, A.; Piguet, C. Optical Sensitization and Upconversion in Discrete Polynuclear Chromium–Lanthanide Complexes. Coord. Chem. Rev. 2012, 256 (15–16), 1644– 1663, DOI: 10.1016/j.ccr.2011.12.013
  16
  Optical sensitization and upconversion in discrete polynuclear chromium-lanthanide complexes
  Aboshyan-Sorgho, Lilit; Cantuel, Martine; Petoud, Stephane; Hauser, Andreas; Piguet, Claude
  Coordination Chemistry Reviews (2012), 256 (15-16), 1644-1663CODEN: CCHRAM; ISSN:0010-8545. (Elsevier B.V.)
  A review. Due to its extreme kinetic inertness, trivalent chromium, Cr(III), has been rarely combined with labile trivalent lanthanides, Ln(III), to give discrete self-assembled (supra)mol. polynuclear complexes. However, the plethora of accessible metal-centered excited states possessing variable lifetimes and emissive properties, combined with the design of efficient intramol. Cr(III) ↔ Ln(III) energy transfer processes open attractive perspectives for programming directional light-conversion within these heterometallic mols. Efforts made to address this exciting challenge for both light-sensitization and light-upconversion are discussed in this article.
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17. 17
  Bernot, K.; Daiguebonne, C.; Calvez, G.; Suffren, Y.; Guillou, O. A Journey in Lanthanide Coordination Chemistry: From Evaporable Dimers to Magnetic Materials and Luminescent Devices. Acc. Chem. Res. 2021, 54 (2), 427– 440, DOI: 10.1021/acs.accounts.0c00684
  17
  A Journey in Lanthanide Coordination Chemistry: From Evaporable Dimers to Magnetic Materials and Luminescent Devices
  Bernot, Kevin; Daiguebonne, Carole; Calvez, Guillaume; Suffren, Yan; Guillou, Olivier
  Accounts of Chemical Research (2021), 54 (2), 427-440CODEN: ACHRE4; ISSN:0001-4842. (American Chemical Society)
  A review. Conspectus: Lanthanide ions are prime ingredients for the design of compds., materials, and devices with unique magnetic and optical properties. Accordingly, coordination chem. is one of the best tools for building mol. edifices from these ions because it allows careful control of the ions' environment and of the dimensionality of the final compd. In this Account, the authors review the authors' results on lanthanide-based dimers. A pure fundamental study on lanthanide coordination chem. allows the study of a full continuum of results from the compd. to materials and then to devices. The conversion of mols. into materials is a tricky task because it requires strong mol. robustness toward the surface deposition processes as well as the preservation and detectability of the mol. properties in the material. Addnl., the passage of a material toward a device implies a material with a given function, for example, a tailored response to an external stimulus. To do so, the authors targeted neutral and isolated mols. whose transfer on surfaces by chemi- or physisorption is much easier than that of charged mols. or extended coordination networks. Then, the authors focused on mols. with very strong evaporability to avoid wet chem. deposition processes that are more likely to damage the mols. and/or distort their geometries. The authors thus designed lanthanide dimers based on fluorinated β-diketonates and pyridine-N-oxide ligands. As expected, they show remarkable evaporability but also strong luminescence and interesting magnetic behavior because they behave as single-mol. magnets (SMMs). Ligand substitutions and stoichiometric modifications allow the optimization of the geometric organization of the dimers in the crystal packing as well as their evaporability, SMM behavior, luminescent properties, or their ability to be anchored on surfaces. Most of all, this family of mols. shows a strong ability to form thick films on various substrates. This allows converting these mols. to magnetic materials and luminescent devices. Magnetic materials can be designed by creating thick films of the dimers deposited on gold. These films were designed and studied with the most advanced techniques of on-surface imaging (at. force microscopy, AFM), on-surface physicochem. characterization (XPS, time of flight-secondary ion mass spectroscopy (Tof-SIMS)), and on-surface magnetic study (low-energy muon spin relaxation (LE-μSR)). Contrary to what was previously obsd. on other SMM films, no depth dependence of the SMM behavior was obsd. This means that the dimers do not suffer from the vacuum or substrate interface and behave similarly, whatever their localization. This exceptional magnetic robustness is a key ingredient in the creation of materials for mol. magnetic data storage. Luminescent devices can be obtained by layering mol. films of the dimers with a copper-rich solid-state electrolyte between ITO/Pt electrodes. The electromigration of Cu2+ ions into films of Eu3+, Tb3+, and Dy3+ dimers quenches their luminescence. This luminescence tuning by electromigration is reversible, and this setup can be considered to be a proof of concept of full solid-state luminescent device where reversible coding can be tailored by an elec. field. It is envisioned for optical data storage purposes. In the future, it could also benefit from the SMM properties of the mols. to pave the way toward multifunctional mol. data storage devices.
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18. 18
  Cucinotta, G.; Perfetti, M.; Luzon, J.; Etienne, M.; Car, P.-E.; Caneschi, A.; Calvez, G.; Bernot, K.; Sessoli, R. Magnetic Anisotropy in a Dysprosium/DOTA Single-Molecule Magnet: Beyond Simple Magneto-Structural Correlations. Angew. Chem., Int. Ed. 2012, 51 (7), 1606– 1610, DOI: 10.1002/anie.201107453
  18
  Magnetic Anisotropy in a Dysprosium/DOTA Single-Molecule Magnet: Beyond Simple Magneto-Structural Correlations
  Cucinotta, Giuseppe; Perfetti, Mauro; Luzon, Javier; Etienne, Mael; Car, Pierre-Emmanuel; Caneschi, Andrea; Calvez, Guillaume; Bernot, Kevin; Sessoli, Roberta
  Angewandte Chemie, International Edition (2012), 51 (7), 1606-1610, S1606/1-S1606/11CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
  Single-crystal magnetic investigations have been shown to be required to study mol. systems that are based on anisotropic lanthanide ions. The detailed exptl. and theor. investigation on one of the most studied lanthanide coordination compds. has provided several key results. The most important one is that simple magnetostructural correlations based on the coordination environment can fail to predict, even approx., the correct magnetic anisotropy of anisotropic lanthanide ions in a low-symmetry environment. Subtle structural details, like the position of hydrogen atoms and the consequent orientation of the nonbonding orbitals of the axial ligand can overcome the symmetry imposed by the coordination polyhedron. The well-resolved luminescence spectra, which allow the energy splitting of the 6H15n multiplet to be detd., have provided precious indications, which confirm that the first excited doublet plays a key role in the magnetization dynamics. .Finally, post Hartree-Fock ab initio calcns. were confirmed to be an invaluable method for the prediction and rationalization of the magnetic anisotropy, provided that subtle structural details are also correctly taken into account. The evaluation of the energy splitting seems, however, even more critically dependent on which structural model and basis sets are used. In modeling the relaxivity effects it is generally assumed that the orientation of the M-Owater of DOTA-like complexes corresponds to the anisotropy axis and that the apical water mols. lie in the cone of highest susceptibility. The authors have shown here that this is probably not the case and we also suspect that the mechanism of contrast in the nuclear relaxation is more complex because the labile water mol. modifies the magnetic anisotropy of the lanthanide ion.
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19. 19
  Shannon, R. D. Revised Effective Ionic Radii and Systematic Studies of Interatomic Distances in Halides and Chaleogenides. Acta Crystallogr., A 1976, 32, 751– 767, DOI: 10.1107/S0567739476001551
  There is no corresponding record for this reference.
20. 20
  Baloch, A. A. B.; Alqahtani, S. M.; Mumtaz, F.; Muqaibel, A. H.; Rashkeev, S. N.; Alharbi, F. H. Extending Shannon’s Ionic Radii Database Using Machine Learning. Phys. Rev. Mater. 2021, 5 (4), 043804 DOI: 10.1103/PhysRevMaterials.5.043804
  20
  Extending Shannon's ionic radii database using machine learning
  Baloch, Ahmer A. B.; Alqahtani, Saad M.; Mumtaz, Faisal; Muqaibel, Ali H.; Rashkeev, Sergey N.; Alharbi, Fahhad H.
  Physical Review Materials (2021), 5 (4), 043804CODEN: PRMHBS; ISSN:2475-9953. (American Physical Society)
  In computational material design, ionic radius is one of the most important phys. parameters used to predict material properties. Motivated by the progress in computational materials science and material informatics, we extend the renowned Shannon's table from 475 ions to 987 ions. Accordingly, a rigorous machine learning (ML) approach is employed to extend the ionic radii table using all possible combinations of oxidn. states (OS) and coordination nos. (CN) available in crystallog. repositories. An ionic-radius regression model for Shannon's database is developed as a function of the period no., the valence orbital configuration, OS, CN, and ionization potential. In the Gaussian process regression (GPR) model, the reached R2 accuracy is 99while the root mean square error of radii is 0.0332 Å. The optimized GPR model is then employed for predicting a new set of ionic radii for uncommon combinations of OS and CN extd. by harnessing crystal structures from materials project databases. The generated data are consolidated with the reputable Shannon's data and are made available online in a database repository.
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21. 21
  Lundberg, D.; Persson, I.; Eriksson, L.; D’Angelo, P.; De Panfilis, S. Structural Study of the N,N′ -Dimethylpropyleneurea Solvated Lanthanoid(III) Ions in Solution and Solid State with an Analysis of the Ionic Radii of Lanthanoid(III) Ions. Inorg. Chem. 2010, 49 (10), 4420– 4432, DOI: 10.1021/ic100034q
  21
  Structural Study of the N,N'-Dimethylpropyleneurea Solvated Lanthanoid(III) Ions in Solution and Solid State with an Analysis of the Ionic Radii of Lanthanoid(III) Ions
  Lundberg, Daniel; Persson, Ingmar; Eriksson, Lars; D'Angelo, Paola; De Panfilis, Simone
  Inorganic Chemistry (2010), 49 (10), 4420-4432CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
  The structures of the N,N'-dimethylpropyleneurea (dmpu) solvated lanthanoid(III) ions have been studied in dmpu soln. (La-Nd, Sm-Lu) and in solid iodide salts (La-Nd, Sm, Gd-Lu) by extended X-ray absorption fine structure (EXAFS), and single crystal X-ray diffraction (La, Pr, Nd, Gd, Tb, Er, Yb, and Lu); the EXAFS studies were performed on both K and LIII absorption edges. Because of the space-demanding properties of dmpu upon coordination, dmpu solvated metal ions often show coordination nos. lower than those found in corresponding hydrates and solvates of oxygen donor solvents without steric requirements beyond the size of the donor atom. All lanthanoid(III) ions are seven-coordinate in soln., except lutetium(III) which is six-coordinated in regular octahedral fashion, whereas in the solid iodide salts the dmpu solvated lanthanoid(III) ions are all six-coordinate in regular octahedral fashion. A comparison of Ln-O bond lengths in a large no. of lanthanoid(III) complexes with neutral oxygen donor ligands and different configurations shows that the metal ion-oxygen distance is specific for each coordination no. with a narrow bond distance distribution. This also shows that the radius of the coordinated oxygen atom in these compds. can be assumed to be 1.34 Å as proposed for coordinated water, while for ethers such as THF it is somewhat larger. Using this at. radius of oxygen in coordinated water mols., we have calcd. the ionic radii of the lanthanoid(III) ions in four- to nine-coordination and evaluated using the bond lengths reported for homo- and heteroleptic complexes in oxygen donor solvates in soln. and solid state. This yields new and revised ionic radii which in some instances are significantly different from the ionic radii normally referenced in the literature, including interpolated values for the elusive promethium(III) ion.
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22. 22
  Seitz, M.; Oliver, A. G.; Raymond, K. N. The Lanthanide Contraction Revisited. J. Am. Chem. Soc. 2007, 129 (36), 11153– 11160, DOI: 10.1021/ja072750f
  22
  The Lanthanide Contraction Revisited
  Seitz, Michael; Oliver, Allen G.; Raymond, Kenneth N.
  Journal of the American Chemical Society (2007), 129 (36), 11153-11160CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
  A complete, isostructural series of complexes with La-Lu (except Pm) with the ligand TREN-1,2-HOIQO (I), [M(TREN-1,2-HOIQO-3H)(H2O)]·H2O, was synthesized and structurally characterized by single-crystal x-ray anal. All complexes are 1-dimensional polymeric species in the solid state, with the lanthanide being in an eight-coordinate, distorted trigonal-dodecahedral environment with a donor set of eight unique oxygen atoms. This series constitutes the 1st complete set of isostructural complexes from La-Lu (without Pm) with a ligand of denticity greater than two. The geometric arrangement of the chelating moieties slightly deviates across the lanthanide series, as analyzed by a shape parameter metric based on the comparison of the dihedral angles along all edges of the coordination polyhedron. The apparent lanthanide contraction in the individual Ln-O bond lengths deviates considerably from the expected quadratic decrease that was found previously in a no. of complexes with ligands of low denticity. The sum of all bond lengths around the trivalent metal cation, however, is more regular, showing an almost ideal quadratic behavior across the entire series. The quadratic nature of the lanthanide contraction is derived theor. from Slater's model for the calcn. of ionic radii. The sum of all distances along the edges of the coordination polyhedron show exactly the same quadratic dependence as the Ln-X bond lengths. The universal validity of this coordination sphere contraction, concomitant with the quadratic decrease in Ln-X bond lengths, was confirmed by reexamn. of four other, previously published series of lanthanide complexes. Owing to the importance of multidentate ligands for the chelation of rare-earth metals, this result provides a significant advance for the prediction and rationalization of the geometric features of the corresponding lanthanide complexes, with great potential impact for all aspects of lanthanide coordination.
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23. 23
  Peters, J. A.; Djanashvili, K.; Geraldes, C. F. G. C.; Platas-Iglesias, C. The Chemical Consequences of the Gradual Decrease of the Ionic Radius along the Ln-Series. Coord. Chem. Rev. 2020, 406, 213146 DOI: 10.1016/j.ccr.2019.213146
  23
  The chemical consequences of the gradual decrease of the ionic radius along the Ln-series
  Peters, Joop A.; Djanashvili, Kristina; Geraldes, Carlos F. G. C.; Platas-Iglesias, Carlos
  Coordination Chemistry Reviews (2020), 406 (), 213146CODEN: CCHRAM; ISSN:0010-8545. (Elsevier B.V.)
  In the periodical system, the lanthanides (the 15 elements in the periodic table between barium and hafnium) are unique in the sense that their trivalent cations have their valence electrons hidden behind the 5s and 5p electrons. They show a gradual decrease in ionic radius with increasing at. no. (also known as the lanthanide contraction). The resulting steric effects det. to a large extent the geometries of complexes of these ions. Here, we discuss these effects, particularly upon the properties of the complexes in aq. soln., for selected families of Ln3+-complexes of oxycarboxylate and aminocarboxylate ligands. The phys. properties of the cations are very different, which is very useful for the elucidation of the configuration, conformation and the dynamics of the complexes by X-ray techniques, NMR spectroscopy, and optical techniques. Often the structural anal. is assisted by computational methods.
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24. 24
  Jordan, R. B. Lanthanide Contraction: What Is Normal?. Inorg. Chem. 2023, 62, 3715– 3721, DOI: 10.1021/acs.inorgchem.2c03674
  24
  Lanthanide Contraction: What is Normal?
  Jordan, Robert B.
  Inorganic Chemistry (2023), 62 (9), 3715-3721CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
  Renewed interest in lanthanide contraction results from its possible effect on the properties and applications of Ln(III) compds. and the theory related to these issues. To understand this effect, it is important to know what is a normal dependence of the contraction on the no. of 4f electrons, n. The normal trend is based on recent values of ionic radii that have a linear dependence on n for coordination nos. (CNs) of 6, 8, and 9. If the normal trend is not followed, then some other interactions in the system are affecting the extent of contraction. However, the suggestion that the variation is curved and fitted by a quadratic function has become popular in recent years. This report examines the Ln(III)-to-ligand atom distances for coordination compds. with CNs of 6-9 and the nitrides and phosphides. Least-squares fits to the linear and quadratic models are applied to all of the bond distances to det. when a quadratic model is justified. The result is that complex systems show a mixt. of linear and quadratic dependencies when individual bond distances are considered and that the linear model is most common and representative of the true lanthanide contraction.
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25. 25
  Bart, S. C. What Is the “Lanthanide Contraction”?. Inorg. Chem. 2023, 62, 3713– 3714, DOI: 10.1021/acs.inorgchem.3c00440
  25
  What is the "Lanthanide Contraction"?
  Bart, Suzanne C.
  Inorganic Chemistry (2023), 62 (9), 3713-3714CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
  There is no expanded citation for this reference.
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26. 26
  Fyfe, W. S. The Problem of Bond Type. Am. Mineral. 1954, 39, 991– 1004
  26
  The problem of bond type
  Fyfe, W. S.
  American Mineralogist (1954), 39 (), 991-1004CODEN: AMMIAY; ISSN:0003-004X.
  cf. C.A. 47, 11868g. Consideration of electronegativities is inadequate for quant. evaluation of the proportions of ionic and covalent bonding in a compd. The overlap integrals give better values, as illustrated for the alkali halides, and by comparison of Si-O and C-O bonds.
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27. 27
  Kawabe, I. Lanthanide Tetrad Effect in the Ln³⁺ Ionic Radii and Refined Spin-Pairing Energy Theory. Geochem. J. 1992, 26 (6), 309– 335, DOI: 10.2343/geochemj.26.309
  27
  Lanthanide tetrad effect in the Ln3+ ionic radii and refined spin-pairing energy theory
  Kawabe, Iwao
  Geochemical Journal (1992), 26 (6), 309-35CODEN: GEJOBE; ISSN:0016-7002.
  The refined spin-pairing energy theory (RSPET) has been improved in order to understand quant. the tetrad or double-double effects recognized in the Ln3+ ionic radii. Since the ionic radii have been detd. from the lattice consts. and structural parameters of LnO1.5 and LnF3, the lattice energies of the compds. and the enthalpy difference of ΔHf°(LnF3) - ΔHf°(LnO1.5) have been examd. by the improved RSPET. The RSPET parameters for the lowest levels of 4fq electronic configurations strongly depend upon the effective nuclear charge (Z*). Such effects due to Z* have been taken into account. This made it possible to sep. the variations in the lattice energies and the enthalpy difference across the Ln3+ series into the following two parts: (1) the large variation as a smooth function of q (the lanthanide contraction trend), and (2) the small zig-zag variation referred to the tetrad or double-double effect. The lattice energy of LnO1.5 and ΔHf°(LnF3) - ΔHf°(LnO1.5) exhibit upward concave tetrad curves in their plots against q of Ln3+. The tetrad effect in the lattice energy of LnF3 is less conspicuous. This means that the Racah parameters for Ln3+ decrease very slightly in going from the gaseous free Ln3+ to LnF3, and then decrease greatly to LnO1.5, in accordance with the nephelauxetic series. The differences in Racah parameters between LnF3 and LnO1.5 have been estd. from ΔHf°(LnF3) - ΔHf°(LnO1.5) by means of an inversion technique based on the improved RSPET. The RSPET results for the thermochem. data are consistent with the careful spectroscopic detns. of Racah parameters for NdF3 and NdO1.5. Both the tetrad effect and the smooth lanthanide contraction seen in the Ln3+ ionic radii can be interpreted in terms of the quantum mech. energetics of 4f electrons.
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28. 28
  Gibbs, G. V.; Tamada, O.; Boisen, M. B., Jr. Atomic and Ionic Radii: A Comparison with Radii Derived from Electron Density Distributions. Phys. Chem. Miner. 1997, 24 (6), 432– 439, DOI: 10.1007/s002690050057
  28
  Atomic and ionic radii: a comparison with radii derived from electron density distributions
  Gibbs, G. V.; Tamada, Osamu; Boisen, M. B., Jr.
  Physics and Chemistry of Minerals (1997), 24 (6), 432-439CODEN: PCMIDU; ISSN:0342-1791. (Springer)
  The bonded radii of anions obtained in topol. analyses of theor. and exptl. electron d. distributions differ from at., ionic and crystal radii in that oxide-, fluoride-, nitride- and sulfide-anion radii are not const. for a given coordination no. They vary in a regular way with bond length and the electronegativity of the cation to which they are bonded, exhibiting radii close to at. radii when bonded to a highly electroneg. cation and radii close to ionic radii when bonded to a highly electropos. cation. The electron d. distributions show that anions are not spherical but exhibit several different radii in different bonded directions. The bonded radii of cations correlate with ionic and at. radii. But unlike ionic radii, the bonded radius of a cation shows a relatively small increase in value with an increase in coordination no. In contrast to at. and ionic radii, the bonded radius of an ion in a crystal or mol. can be used as a reliable and well-defined est. of its radius in the direction of its bonds.
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29. 29
  Gibbs, G. V.; Ross, N. L.; Cox, D. F.; Rosso, K. M.; Iversen, B. B.; Spackman, M. A. Bonded Radii and the Contraction of the Electron Density of the Oxygen Atom by Bonded Interactions. J. Phys. Chem. A 2013, 117 (7), 1632– 1640, DOI: 10.1021/jp310462g
  29
  Bonded Radii and the Contraction of the Electron Density of the Oxygen Atom by Bonded Interactions
  Gibbs, Gerald V.; Ross, Nancy L.; Cox, David F.; Rosso, Kevin M.; Iversen, Bo B.; Spackman, Mark A.
  Journal of Physical Chemistry A (2013), 117 (7), 1632-1640CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)
  The bonded radii for more than 700 bonded pairs of atoms, comprising more than 50 oxide crystals, extd. from exptl. and theor. electron d. distributions, are averaged and compared with the ionic radii for first, second, and third row atoms. At odds with the assumption of a fixed ionic radius of 1.40 Å for the oxide anion, the bonded radius for the anion, rb(O), decreases systematically from 1.40 to 0.65 Å as the electron d. distribution of the atom is progressively polarized and contracted by its bonded interactions. The radii for the more electropos. metal atoms agree with the ionic radii when the electron d. distribution of the anion is largely unpolarized by its bonded interactions. However, those for the more electroneg. metal atoms are progressively larger than the ionic radii as the electron d. distribution of the anion is progressively polarized and contracted along the bond vectors with decreasing bond length. The progressive decrease of rb(O) indicates that the compilation of sets of ionic radii, based on a fixed radius for the oxide anion, is problematic and impacts the accuracy of the ionic radii for the metal atoms. The assumption of a fixed radius for the anion, made in the derivation of sets of radii, not only results in unrealistic neg. ionic radii for the more electroneg. atoms but also in ionic radii that are as much as 0.5 Å smaller than the bonded radii, particularly for the more electroneg. M atoms. The lack of agreement between the ionic and the bonded radii for the more shared bonded interactions is ascribed to the progressive increase in the polarization and contraction of the electron d. of the oxide anion by the bonded interactions with a concomitant decrease in the radius of the anion, a factor that was largely neglected in the compilation of the ionic radii for fluoride, oxide, sulfide, and nitride crystals. The close agreement of the bonded radii and procrystal bonded radii is consistent with the argument that the chem. forces that govern the electron d. distributions and bonded radii are largely at. in nature, resulting in comparable electron d. distributions.
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30. 30
  Rahm, M.; Hoffmann, R.; Ashcroft, N. W. Atomic and Ionic Radii of Elements 1–96. Chem. – Eur. J. 2016, 22 (41), 14625– 14632, DOI: 10.1002/chem.201602949
  30
  Atomic and Ionic Radii of Elements 1-96
  Rahm, Martin; Hoffmann, Roald; Ashcroft, N. W.
  Chemistry - A European Journal (2016), 22 (41), 14625-14632CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)
  Atomic and cationic radii have been calcd. for the first 96 elements, together with selected anionic radii. The metric adopted is the av. distance from the nucleus where the electron d. falls to 0.001 electrons per bohr3, following earlier work by Boyd. Our radii are derived using relativistic all-electron d. functional theory calcns., close to the basis set limit. They offer a systematic quant. measure of the sizes of non-interacting atoms, commonly invoked in the rationalization of chem. bonding, structure, and different properties. Remarkably, the at. radii as defined in this way correlate well with van der Waals radii derived from crystal structures. A rationalization for trends and exceptions in those correlations is provided.
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31. 31
  Liu, J.-B.; Schwarz, W. H. E.; Li, J. On Two Different Objectives of the Concepts of Ionic Radii. Chem. – Eur. J. 2013, 19 (44), 14758– 14767, DOI: 10.1002/chem.201300917
  31
  On Two Different Objectives of the Concepts of Ionic Radii
  Liu, Jian-Biao; Schwarz, W. H. Eugen; Li, Jun
  Chemistry - A European Journal (2013), 19 (44), 14758-14767CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)
  Exptl. and theor. derived interat. distances (D) and ionic radii (R) of more than a hundred monomeric (AX), dimeric (A2X2, ABXY), and cryst. ([AX]) alkali halide species (A=Li, Na, K, Rb, Cs, Fr; X=H, F, Cl, Br, I, At) have been analyzed. Chemists use the word "at. radius" for two antithetic concepts. Let DCiEE'jj' be the "billion" of distances i between two adjacent atoms in the millions of known compds. C from a hundred different elements E in bonding states j. The common chem. aim is partitioning D approx. into increments REj + RE'j'. This can be achieved with a few (say <thousand) predictive consts. REj. An antipodal aim is specifying in hindsight an electron d. feature in the "billion" of different bonds i, by partitioning them into "two billions" of exact bonded radii RECi + RE'Ci. The const. incremental and the variable bonded radii concepts with the same generic name are useful in different fields of research. Different concepts should be well distinguished, since they have different meaning, different numerical values, and different purposes.
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32. 32
  Cordero, B.; Gómez, V.; Platero-Prats, A. E.; Revés, M.; Echeverría, J.; Cremades, E.; Barragán, F.; Alvarez, S. Covalent Radii Revisited. Dalton Trans. 2008, 21, 2832– 2838, DOI: 10.1039/b801115j
  There is no corresponding record for this reference.
33. 33
  Pyykkö, P.; Atsumi, M. Molecular Single-Bond Covalent Radii for Elements 1–118. Chem. – Eur. J. 2009, 15 (1), 186– 197, DOI: 10.1002/chem.200800987
  There is no corresponding record for this reference.
34. 34
  Pyykkö, P. Additive Covalent Radii for Single-, Double-, and Triple-Bonded Molecules and Tetrahedrally Bonded Crystals: A Summary. J. Phys. Chem. A 2015, 119 (11), 2326– 2337, DOI: 10.1021/jp5065819
  34
  Additive Covalent Radii for Single-, Double-, and Triple-Bonded Molecules and Tetrahedrally Bonded Crystals: A Summary
  Pyykko, Pekka
  Journal of Physical Chemistry A (2015), 119 (11), 2326-2337CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)
  A review. The recent fits of additive covalent radii RAB = rA + rB for the title systems are reviewed and compared with alternative systems of radii by other authors or with further exptl. data. The agreement of the predicted R with expt. is good, provided that the A-B bond is not too ionic, or the coordination nos. of the two atoms too different from the original input data, used in the fit. Bonds between transition metals and halides are not included in the single-bond set, because of their partial multiple-bond character.
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35. 35
  Gunnlaugsson, T.; Leonard, J. P.; Mulready, S.; Nieuwenhuyzen, M. Three Step vs One Pot Synthesis and X-Ray Crystallographic Investigation of Heptadentate Triamide Cyclen (1,4,7,10-Tetraazacyclododecane) Based Ligands and Some of Their Lanthanide Ion Complexes. Tetrahedron 2004, 60 (1), 105– 113, DOI: 10.1016/j.tet.2003.10.086
  35
  Three step vs. one pot synthesis and X-ray crystallographic investigation of heptadentate triamide cyclen (1,4,7,10-tetraazacyclododecane) based ligands and some of their lanthanide ion complexes
  Gunnlaugsson, Thorfinnur; Leonard, Joseph P.; Mulready, Sinead; Nieuwenhuyzen, Mark
  Tetrahedron (2004), 60 (1), 105-113CODEN: TETRAB; ISSN:0040-4020. (Elsevier Science B.V.)
  The synthesis of several lanthanide complexes from the tris alkylated cyclen (1,4,7,10-tetraazacyclododecane) ligands (I, R = Me, 1;R = H, 2) is described. The prepn. of 1 and 2 were studied by two different synthetic routes (Methods 1 and 2). The 1st of these involves the mono protection of cyclen using 4-methoxyphenylsulfonyl chloride, followed by alkylation of the remaining three secondary amines of cyclen, and deprotection using solvated Na(s). Using this approach only 1 was successfully formed. The x-ray crystal structure of the intermediate, (II = 9) and the corresponding La(III) complex, 9·La is presented. The 2nd method involved the direct synthesis of the two ligands in a single step. The x-ray crystallog. of the Eu(III) complex of one of these ligands is presented. Whereas, Method 1 yielded the product 1 in high purity, but in low overall yield, Method 2 gave higher yields for both ligands (∼50% for both).
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36. 36
  Amin, S.; Morrow, J. R.; Lake, C. H.; Churchill, M. R. Lanthanide(III) Tetraamide Macrocyclic Complexes as Synthetic Ribonucleases: Structure and Catalytic Properties of[La(Tcmc)(CF3SO3)(EtOH)](CF3SO3)2. Angew. Chem., Int. Ed. 1994, 33 (7), 773– 775, DOI: 10.1002/anie.199407731
  There is no corresponding record for this reference.
37. 37
  Franklin, S. J.; Raymond, K. N. Solution Structure and Dynamics of Lanthanide Complexes of the Macrocyclic Polyamino Carboxylate DTPA-Dien. NMR Study and Crystal Structures of the Lanthanum(III) and Europium(III) Complexes. Inorg. Chem. 1994, 33 (25), 5794– 5804, DOI: 10.1021/ic00103a029
  37
  Solution Structure and Dynamics of Lanthanide Complexes of the Macrocyclic Polyamino Carboxylate DTPA-dien. NMR Study and Crystal Structures of the Lanthanum(III) and Europium(III) Complexes
  Franklin, Sonya J.; Raymond, Kenneth N.
  Inorganic Chemistry (1994), 33 (25), 5794-804CODEN: INOCAJ; ISSN:0020-1669.
  An 18-membered macrocyclic DTPA-bis(amide) ligand (I; DTPA = diethylenetriaminepentaacetic acid) contg. a heteroatom in the amide link was prepd. via the condensation of DTPA-dianhydride and diethylenetriamine. The soln. structures of the two isomeric pairs present in the Ln(III) complexes of DTPA-dien were studied by 1H NMR. One enantiomeric pair exhibits slow exchange on the NMR time scale at low temps. (0-25°) and dynamic behavior at higher temps. The other isomeric pair exhibits an unusual static behavior; exchange remains slow even at 95°. Peak assignments for the Eu(DTPA-dien) spectra are given based on deuteration studies, 2-dimensional COSY spectroscopy, and 2-dimensional EXSY spectroscopy. 2D EXSY spectroscopy at several temps. and mixing times showed that ΔG⧧299 for the dynamic isomerization is 57.5 ± 0.3 kJ/mol, and that the dynamic isomer is an intermediate for the static isomerization, which occurs with a change in backbone amine chirality. The structures of the La(III) and Eu(III) DTPA-dien complexes were detd. by x-ray anal. [La(DTPA-dienH+)H2O]2(CF3SO3-)2·18H2O crystallizes as a carboxylate-bridged dimer about a center of inversion in the orthorhombic space group Pbca with a 12.626(2), b 21.405(3), c 26.422(9) Å, and Z = 8. Each La ion is 11-coordinate with octadentate ligand coordination, an η2 bridging carboxylate, and one H2O. [Eu(DTPA-dienH+)]4(CF3SO3-)4·6NaCF3SO3·20H2O crystallizes as a carboxylate-bridged tetramer with two crystallog. independent Eu(III) positions (Z = 8 for each) in the monoclinic space group C2/c: a 30.94(1), b 23.456(3), c 22.611(4) Å, β 105.78(2)°. The coordination geometries about Eu1 and Eu2 are nearly identical and are described as a nine-coordinate tricapped trigonal prism with octadentate ligand coordination plus an η1 bridging carboxylate. The tendency to oligomerize is attributed to the constraints imposed by the macrocycle and the H bonding available with the link heteroatom. The structural differences between the two complexes are attributed to a difference in La(III) and Eu(III) ionic size. The soln. structure of the dynamic isomer is the same as the monomer unit of the crystal structures, and the static isomer is similar, save for a change in one terminal backbone nitrogens' chirality.
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38. 38
  Nakai, H.; Nonaka, K.; Goto, T.; Seo, J.; Matsumoto, T.; Ogo, S. A Macrocyclic Tetraamine Bearing Four Phenol Groups: A New Class of Heptadentate Ligands to Provide an Oxygen-Sensitive Luminescent Tb(iii) Complex with an Extendable Phenol Pendant Arm. Dalton Trans. 2015, 44 (24), 10923– 10927, DOI: 10.1039/C5DT00816F
  38
  A macrocyclic tetraamine bearing four phenol groups: a new class of heptadentate ligands to provide an oxygen-sensitive luminescent Tb(III) complex with an extendable phenol pendant arm
  Nakai, Hidetaka; Nonaka, Kyoshiro; Goto, Takahiro; Seo, Juncheol; Matsumoto, Takahiro; Ogo, Seiji
  Dalton Transactions (2015), 44 (24), 10923-10927CODEN: DTARAF; ISSN:1477-9226. (Royal Society of Chemistry)
  This paper presents a 1,4,7,10-teraazacyclododecane-based tetrakis-phenol (H4L) as a protonated ligand precursor and its oxygen-sensitive luminescent terbium(III) complex with an extendable phenol pendant arm (Φ = 0.91 under N2, Φ = 0.031 under air), in which the potentially N4O4-octadentate ligand unprecedentedly coordinates to the Tb3+ ion in a N4O3-heptadentate fashion (1, TbL).
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39. 39
  Wen, H.-R.; Zhang, J.-L.; Liang, F.-Y.; Yang, K.; Liu, S.-J.; Liu, C.-M. Multifunctional Lanthanide Complexes Based on Tetraazacyclolamidophenol Ligand with Field-Induced Slow Magnetic Relaxation, Luminescent and SHG Properties: Multifunctional Lanthanide Complexes Based on Tetraazacyclolamidophenol Ligand with Field-Induced Slow Magnetic Relaxation, Luminescent and SHG Proper. Eur. J. Inorg. Chem. 2019, 2019 (10), 1406– 1412, DOI: 10.1002/ejic.201801492
  39
  Multifunctional Lanthanide Complexes Based on Tetraazacyclolamidophenol Ligand with Field-Induced Slow Magnetic Relaxation, Luminescent and SHG Properties
  Wen, He-Rui; Zhang, Jia-Li; Liang, Fu-Yong; Yang, Kai; Liu, Sui-Jun; Liu, Cai-Ming
  European Journal of Inorganic Chemistry (2019), 2019 (10), 1406-1412CODEN: EJICFO; ISSN:1434-1948. (Wiley-VCH Verlag GmbH & Co. KGaA)
  Two multifunctional lanthanide complexes, [Dy(HL)]·MeOH (1) and [Er(HL)]·MeOH (2), [H4L = N,N',N'',N'''-tetra(3,5-dimethyl-2-Hydroxybenzyl)-1,4,7,10-tetraazacyclododecane] were synthesized and structurally characterized. Complexes 1 and 2 are isomorphic and crystallize in the noncentrosym. orthorhombic space group Pca21. Their structure consists of one seven-coordinated LnIII ion with the coordination geometry of trigonal prism, one HL3- ligand and one lattice MeOH mol. They exhibit 2nd-harmonic generation (SHG) effect. Complex 1 displays strong fluorescent emissions, which are typical narrow emission bands of lanthanide ions. Complex 1 features field-induced slow magnetic relaxation behavior. Therefore, complex 1 may be a potential multifunctional mol. material.
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40. 40
  Urbanovský, P.; Kotek, J.; Císařová, I.; Hermann, P. The Solid-State Structures and Ligand Cavity Evaluation of Lanthanide(III) Complexes of a DOTA Analogue with a (Dibenzylamino)Methylphosphinate Pendant Arm. Dalton Trans. 2020, 49 (5), 1555– 1569, DOI: 10.1039/C9DT04056K
  40
  The solid-state structures and ligand cavity evaluation of lanthanide(III) complexes of a DOTA analogue with a (dibenzylamino)methylphosphinate pendant arm
  Urbanovsky, Peter; Kotek, Jan; Cisarova, Ivana; Hermann, Petr
  Dalton Transactions (2020), 49 (5), 1555-1569CODEN: DTARAF; ISSN:1477-9226. (Royal Society of Chemistry)
  A series of lanthanide(III) complexes of a monophosphinate analog of H4dota, 1,4,7,10-tetraazacyclododecane-1,4,7-triacetic-10-methyl[(N,N-dibenzylamino)methyl]phosphinic acid (H4do3apDBAm = H4L1), were prepd. and their solid-state structures were studied using single-crystal X-ray diffraction. In all structures, the ligand anion was octadentately coordinated to the Ln(III) or Sc(III) ions similarly to other DOTA-like ligands, i.e. forming parallel N4- and O4-planes. The lighter lanthanide(III) complexes (till dysprosium) were nonacoordinated in the twisted square-antiprismatic (TSA) configuration with the apical coordination of water mols. or oxygen atoms from the neighboring complex unit. The heavier lanthanide(III) complexes (from terbium) were found as the "anhyd." octacoordinated twisted square-antiprismatic (TSA') isomer. For the terbium(III) ion, both forms were structurally characterized. The structural data of the Ln(III)-H4L1 complexes and complexes of several related DOTA-like ligands were analyzed. It clearly showed that the structural parameters for the square-antiprismatic (SA) isomers were clustered in a small range while those for the TSA/TSA' isomers were significantly more spread. The anal. also gave useful information about the influence of various pendant arms on the structure of the complexes of the DOTA-like ligands. The twist angle (torsion) of the chelate ring contg. a larger phosphorus atom was similar to those of the remaining three acetate pendants. It led to a larger sepn. of the N4···O4 planes and to smaller trans-O-Ln-O angles than the parameters found in the complexes of H4dota and its tetraamide derivs. dotam(R). It resulted in a relatively long bond between the metal ion and the coordinated water mol. It led, together with the neg. charge of the oxygen atoms forming the O4-plane, to an extremely fast water exchange rate reported for the Gd(III)-H4L1 complex and, generally, to a fast water exchange of Gd(III) complexes with the monophosphorus acid analogs of H4dota, H5do3ap/H4do3apR.
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41. 41
  Woods, M.; Payne, K. M.; Valente, E. J.; Kucera, B. E.; Young, V. G. Crystal Structures of DOTMA Chelates from Ce³⁺ to Yb³⁺: Evidence for a Continuum of Metal Ion Hydration States. Chem. – Eur. J. 2019, 25 (42), 9997– 10005, DOI: 10.1002/chem.201902068
  41
  Crystal Structures of DOTMA Chelates from Ce3+ to Yb3+: Evidence for a Continuum of Metal Ion Hydration States
  Woods, Mark; Payne, Katherine M.; Valente, Edward J.; Kucera, Benjamin E.; Young, Victor G. Jr.
  Chemistry - A European Journal (2019), 25 (42), 9997-10005CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)
  The crystal structures of chelates formed between each stable paramagnetic lanthanide ion and the octadentate polyamino carboxylate ligand DOTMA are described. A total of 23 individual chelates structures were obtained; in each chelate the coordination geometry around the metal ion is best described as a twisted square antiprism (torsion angle -25.0°--31.4°). Despite the uniformity of the general coordination geometry provided by the DOTMA ligand, there is a considerable variation in the hydration state of each chelate. The early Ln3+ chelates are assocd. with a single inner sphere water mol.; the Ln-OH2 interaction is remarkable for being very long. After a clear break at gadolinium, the no. of chelates in the unit cell that have a water mol. interacting with the Ln3+ decreases linearly until at Tm3+ no water is found to interact with the metal ion. The Ln-OH2 distance obsd. in the chelates of the later Ln3+ ions are also extremely long and increase as the ions contract (2.550-2.732 Å). No clear break between hydrated and dehydrated chelates is obsd.; rather this series of chelates appear to represent a continuum of hydration states in which the ligand gradually closes around the metal ion as its ionic radius decreases (with decreased hydration) and the metal drops down into the coordination cage.
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42. 42
  Starynowicz, P. Complexes of Divalent Europium with Dotp and Dotpph. New J. Chem. 2021, 45 (13), 5879– 5889, DOI: 10.1039/D1NJ00393C
  42
  Complexes of divalent europium with dotp and dotpph
  Starynowicz, Przemyslaw
  New Journal of Chemistry (2021), 45 (13), 5879-5889CODEN: NJCHE5; ISSN:1144-0546. (Royal Society of Chemistry)
  Two complexes of divalent europium, with 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrakis(methylene phosphonate) (dotp) and 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrakis(methylene P-phenylphosphinate) (dotpph), were obtained by electrochem. synthesis. In both compds., the Eu2+ cation is 8-coordinate, surrounded by 4 oxygen atoms from phosphonate or phosphinate groups and 4 nitrogen atoms. The complex with dotp shows green luminescence at 77 K, while in the dotpph complex the emission is almost completely quenched. The TD DFT calcns. suggest that in both complexes the emission is of anomalous character: s → f for the first complex and π* → f for the other. Polarog. half-wave potentials of both complexes are similar to those of Eu aminopolycarboxylates. The Eu-O bonds, analyzed using topol. methods, are ionic; the Eu-N bonds in the first complex show a certain degree of covalency, while in the other one they are ionic.
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43. 43
  Basal, L. A.; Bailey, M. D.; Romero, J.; Ali, M. M.; Kurenbekova, L.; Yustein, J.; Pautler, R. G.; Allen, M. J. Fluorinated Eu^II -Based Multimodal Contrast Agent for Temperature- and Redox-Responsive Magnetic Resonance Imaging. Chem. Sci. 2017, 8 (12), 8345– 8350, DOI: 10.1039/C7SC03142D
  43
  Fluorinated EuII-based multimodal contrast agent for temperature- and redox-responsive magnetic resonance imaging
  Basal, Lina A.; Bailey, Matthew D.; Romero, Jonathan; Ali, Meser M.; Kurenbekova, Lyazat; Yustein, Jason; Pautler, Robia G.; Allen, Matthew J.
  Chemical Science (2017), 8 (12), 8345-8350CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)
  Magnetic resonance imaging (MRI) using redox-active, EuII-contg. complexes is one of the most promising techniques for noninvasively imaging hypoxia in vivo. In this technique, pos. (T1-weighted) contrast enhancement persists in areas of relatively low oxidizing ability, such as hypoxic tissue. Herein, we describe a fluorinated, EuII-contg. complex in which the redox-active metal is caged by intramol. interactions. The position of the fluorine atoms enables temp.-responsive contrast enhancement in the reduced form of the contrast agent and detection of the oxidized contrast agent via MRI in vivo. Pos. contrast is obsd. in 1H-MRI with Eu in the +2 oxidn. state, and chem. exchange satn. transfer and 19F-MRI signal are obsd. with Eu in the +3 oxidn. state. Contrast enhancement is controlled by the redox state of Eu, and modulated by the fluorous interactions that cage a bound water mol. reduce relaxivity in a temp.-dependent fashion. Together, these advancements constitute the first report of in vivo, redox-responsive imaging using 19F-MRI.
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44. 44
  Burai, L.; Tóth, É.; Seibig, S.; Scopelliti, R.; Merbach, A. E. Solution and Solid-State Characterization of EuII Chelates: A Possible Route Towards Redox Responsive MRI Contrast Agents. Chem. – Eur. J. 2000, 6 (20), 3761– 3770, DOI: 10.1002/1521-3765(20001016)6:20<3761::AID-CHEM3761>3.0.CO;2-6
  44
  Solution and solid-state characterization of EuII chelates: a possible route towards redox responsive MRI contrast agents
  Burai, Laszlo; Toth, Eva; Seibig, Sabine; Scopelliti, Rosario; Merbach, Andre E.
  Chemistry - A European Journal (2000), 6 (20), 3761-3770CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH)
  We report the first solid state X-ray crystal structure for a EuII chelate, [C(NH2)3]3[EuII(DTPA)(H2O)]·8H2O, in comparison with those for the corresponding Sr analog, [C(NH2)3]3[Sr(DTPA)(H2O)]·8H2O and for [Sr(ODDA)]·8H2O (DTPA5- = diethylenetriamine-N,N,N',N",N"-pentaacetate, ODDA2- = 1,4,10,13-tetraoxa-7,16-diaza-cyclooctadecane-7,16-diacetate). The two DTPA complexes are isostructural due to the similar ionic size and charge of Sr2+ and Eu2+. The redox stability of [EuII(ODDA)(H2O)] and [EuII(ODDM)]2- complexes has been investigated by cyclovoltammetry and UV/Vis spectrophotometry (ODDM4- = 1,4,10,13-tetraoxa-7,16-diaza-cyclooctadecane-7,16-dimalonate). The macrocyclic complexes are much more stable against oxidn. than [EuII(DTPA)(H2O)]3- (the redox potentials are E1/2 = -0.82 V, -0.92 V, and -1.35 V vs. Ag/AgCl electrode for [EuIII/II(ODDA)(H2O)], [EuIII/II(ODDM)], and [EuIII/II(DTPA)(H2O)], resp., compared with -0.63 V for EuIII/II aqua). The thermodn. stability consts. of [EuII(ODDA)(H2O)], [EuII(ODDM)]2-, [Sr(ODDA)(H2O)], and [Sr(ODDM)]2- were also detd. by pH potentiometry. They are slightly higher for the EuII complexes than those for the corresponding Sr analogs (logKML = 9.85, 13.07, 8.66, and 11.34 for [EuII(ODDA)(H2O)], [EuII(ODDM)]2-, [Sr(ODDA)(H2O)], and [Sr(ODDM)]2-, resp., 0.1 M (CH3)4NCl). The increased thermodn. and redox stability of the EuII complex formed with ODDA as compared with the traditional ligand DTPA can be of importance when biomedical application is concerned. A variable-temp. 17O-NMR and 1H-nuclear magnetic relaxation dispersion (NMRD) study has been performed on [EuII(ODDA)(H2O)] and [EuII(ODDM)]2- in aq. soln. [EuII(ODDM)]2- has no inner-sphere water mol. which allowed us to use it as an outer-sphere model for [EuII(ODDA)(H2O)]. The water exchange rate (kex298 = 0.43 × 109 s-1) is one third of that obtained for [EuII(DTPA)(H2O)]3-. The variable pressure 17O-NMR study yielded a neg. activation vol., Δν = -3.9 cm3mol-1; this indicates associatively activated water exchange. This water exchange rate is in the optimal range to attain max. proton relaxivities, which are, however, strongly limited by the fast rotation of the small mol. wt. complex.
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45. 45
  Dovrat, G.; Pevzner, S.; Maimon, E.; Vainer, R.; Iliashevsky, O.; Ben-Eliyahu, Y.; Moisy, P.; Bettelheim, A.; Zilbermann, I. DOTP versus DOTA as Ligands for Lanthanide Cations: Novel Structurally Characterized Ce^IV and Ce^III Cyclen-Based Complexes and Clusters in Aqueous Solutions. Chem. – Eur. J. 2022, 28 (61), e20221868 DOI: 10.1002/chem.202201868
  There is no corresponding record for this reference.
46. 46
  Rodríguez-Rodríguez, A.; Regueiro-Figueroa, M.; Esteban-Gómez, D.; Rodríguez-Blas, T.; Patinec, V.; Tripier, R.; Tircsó, G.; Carniato, F.; Botta, M.; Platas-Iglesias, C. Definition of the Labile Capping Bond Effect in Lanthanide Complexes. Chem. – Eur. J. 2017, 23 (5), 1110– 1117, DOI: 10.1002/chem.201604390
  46
  Definition of the Labile Capping Bond Effect in Lanthanide Complexes
  Rodriguez-Rodriguez, Aurora; Regueiro-Figueroa, Martin; Esteban-Gomez, David; Rodriguez-Blas, Teresa; Patinec, Veronique; Tripier, Raphael; Tircso, Gyula; Carniato, Fabio; Botta, Mauro; Platas-Iglesias, Carlos
  Chemistry - A European Journal (2017), 23 (5), 1110-1117CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)
  Two macrocyclic ligands contg. a cyclen unit, a Me group, a picolinate arm, and two acetate pendant arms attached to two nitrogen atoms of the macrocycle either in trans (1,7-H3Medo2 ampa = 2,2'-(7-((6-carboxypyridin-2-yl)methyl)-10-methyl-1,4,7,10-tetraazacyclododecane-1,4-diyl)diacetic acid) or in cis (1,4-H3Medo2 ampa) positions are reported. These ligands provide eight-coordination to the Ln3+ ions, leaving a coordination position available for a water mol. that occupies a capping position in the twisted square antiprismatic polyhedron (1,4-H3Medo2 ampa) or one of the positions of the square antiprism (1,7-H3Medo2 ampa). The charge neutral [Gd(1,7-Medo2 ampa)] complex presents an unprecedentedly low water-exchange rate (kex298=8.8 × 103 s-1), whereas water exchange in [Gd(1,4-Medo2 ampa)] is three orders of magnitude faster (kex298=6.6 × 106 s-1). These results showcase the labile capping bond phenomenon: A ligand occupying a capping position is hindered by the environment and thus is intrinsically labile.
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47. 47
  Caravan, P.; Esteban-Gómez, D.; Rodríguez-Rodríguez, A.; Platas-Iglesias, C. Water Exchange in Lanthanide Complexes for MRI Applications. Lessons Learned over the Last 25 Years. Dalton Trans. 2019, 48 (30), 11161– 11180, DOI: 10.1039/C9DT01948K
  47
  Water exchange in lanthanide complexes for MRI applications. Lessons learned over the last 25 years
  Caravan, Peter; Esteban-Gomez, David; Rodriguez-Rodriguez, Aurora; Platas-Iglesias, Carlos
  Dalton Transactions (2019), 48 (30), 11161-11180CODEN: DTARAF; ISSN:1477-9226. (Royal Society of Chemistry)
  The water exchange rates of water mols. coordinated to the metal ion in lanthanide complexes have been profusely investigated during the last 25 years, esp. in the case of Gd3+ and Eu3+ complexes. This is mainly related to the important application of some Gd3+ complexes as contrast agents in magnetic resonance imaging (MRI), and the intensive investigation of Eu3+ complexes as contrast agent candidates providing contrast through the chem. exchange satn. transfer mechanism (CEST). Both applications require a fine tunning of the exchange rate of the coordinated water mol. to yield optimal response. Herein we review the progress made in this field to control water exchange in a rational way through ligand design, providing relationships between the obsd. trends, the structures of the complexes and the mechanisms responsible for the water exchange reaction.
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48. 48
  Garda, Z.; Nagy, V.; Rodríguez-Rodríguez, A.; Pujales-Paradela, R.; Patinec, V.; Angelovski, G.; Tóth, É.; Kálmán, F. K.; Esteban-Gómez, D.; Tripier, R.; Platas-Iglesias, C.; Tircsó, G. Unexpected Trends in the Stability and Dissociation Kinetics of Lanthanide(III) Complexes with Cyclen-Based Ligands across the Lanthanide Series. Inorg. Chem. 2020, 59 (12), 8184– 8195, DOI: 10.1021/acs.inorgchem.0c00520
  48
  Unexpected Trends in the Stability and Dissociation Kinetics of Lanthanide(III) Complexes with Cycle-Based Ligands across the Lanthanide Series
  Garda, Zoltan; Nagy, Viktoria; Rodriguez-Rodriguez, Aurora; Pujales-Paradela, Rosa; Patinec, Veronique; Angelovski, Goran; Toth, Eva; Kalman, Ferenc K.; Esteban-Gomez, David; Tripier, Raphael; Platas-Iglesias, Carlos; Tircso, Gyula
  Inorganic Chemistry (2020), 59 (12), 8184-8195CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
  We report a detailed study of the thermodn. stability and dissocn. kinetics of lanthanide complexes with two ligands contg. a cyclen unit, a Me group, a picolinate arm, and two acetate pendant arms linked to two nitrogen atoms of the macrocycle in either cis (1,4-H3DO2APA) or trans (1,7-H3DO2APA) positions. The stability consts. of the Gd3+ complexes with these two ligands are very similar, with log KGdL values of 16.98 and 16.33 for the complexes of 1,4-H3DO2APA and 1,7-H3DO2APA, resp. The stability consts. of complexes with 1,4-H3DO2APA follow the usual trend, increasing from log KLaL = 15.96 to log KLuL = 19.21. However, the stability of [Ln(1,7-DO2APA)] complexes decreases from log K = 16.33 for Gd3+ to 14.24 for Lu3+. The acid-catalyzed dissocn. rates of the Gd3+ complexes differ by a factor of ∼ 15, with rate consts. (k1) of 1.42 and 23.5 M-1 s-1 for [Gd(1,4-DO2APA)] and [Gd(1,7-DO2APA)], resp. This difference is magnified across the lanthanide series to reach a 5 orders of magnitude higher k1 for [Yb(1,7-DO2APA)] (1475 M-1 s-1) than for [Yb(1,4-DO2APA)] (5.79 x 10-3 M-1 s-1). The acid-catalyzed mechanism involves the protonation of a carboxylate group, followed by a cascade of proton-transfer events that result in the protonation of a nitrogen atom of the cyclen unit. D. functional theory calcns. suggest a correlation between the strength of the Ln-Ocarboxylate bonds and the kinetic inertness of the complex, with stronger bonds providing more inert complexes. The 1H NMR resonance of the coordinated water mol. in the [Yb(1,7-DO2APA)] complex at 176 ppm provides a sizable chem. exchange satn. transfer effect thanks to a slow water exchange rate of (15.9 ± 1.6) x 103 s-1. The arrangement of the ligand donor atoms around the lanthanide ion provokes dramatic differences in the thermodn. stabilities and dissocn. kinetics of lanthanide complexes, as demonstrated by investigating the complexes with two isomeric cyclen-based ligands, contg. a picolinate arm and two acetate arms in either positions 1,7 or 1,4 of the macrocyclic structure.
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49. 49
  Jannin, S.; Helm, L.; Bodenhausen, G. Kinetics of Yttrium–Ligand Complexation Monitored Using Hyperpolarized ⁸⁹ Y as a Model for Gadolinium in Contrast Agents. J. Am. Chem. Soc. 2010, 132 (14), 5006– 5007, DOI: 10.1021/ja1013954
  49
  Kinetics of Yttrium-Ligand Complexation Monitored Using Hyperpolarized 89Y as a Model for Gadolinium in Contrast Agents
  Mieville, Pascal; Jannin, Sami; Helm, Lothar; Bodenhausen, Geoffrey
  Journal of the American Chemical Society (2010), 132 (14), 5006-5007CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
  Hyperpolarization by dissoln. dynamic nuclear polarization (DNP) enhances 89Y spin magnetization by 3 to 4 orders of magnitude and provides a way to monitor yttrium-ligand complexation "on the fly" by means of 89Y NMR. In this communication, we show an example of free yttrium Y3+ being complexed with 1,4,7,10-tetrakis(acetamido)-1,4,7,10-tetraazacyclododecane (DOTAM) to form [Y(DOTAM)(H2O)]3+ as a model for gadolinium in contrast agents.
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50. 50
  Tickner, B. J.; Stasiuk, G. J.; Duckett, S. B.; Angelovski, G. The Use of Yttrium in Medical Imaging and Therapy: Historical Background and Future Perspectives. Chem. Soc. Rev. 2020, 49 (17), 6169– 6185, DOI: 10.1039/C9CS00840C
  50
  The use of yttrium in medical imaging and therapy: historical background and future perspectives
  Tickner Ben J; Stasiuk Graeme J; Duckett Simon B; Angelovski Goran
  Chemical Society reviews (2020), 49 (17), 6169-6185 ISSN:.
  Yttrium is a chemically versatile rare earth element that finds use in a range of applications including lasers and superconductors. In medicine, yttrium-based materials are used in medical lasers and biomedical implants. This is extended through the array of available yttrium isotopes to enable roles for (90)Y complexes as radiopharmaceuticals and (86)Y tracers for positron emission tomography (PET) imaging. The naturally abundant isotope (89)Y is proving to be suitable for nuclear magnetic resonance investigations, where initial reports in the emerging field of hyperpolarised magnetic resonance imaging (MRI) are promising. In this review we explore the coordination and radiochemical properties of yttrium, and its role in drugs for radiotherapy, PET imaging agents and perspectives for applications in hyperpolarised MRI.
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51. 51
  Vaughn, B. A.; Koller, A. J.; Chen, Z.; Ahn, S. H.; Loveless, C. S.; Cingoranelli, S. J.; Yang, Y.; Cirri, A.; Johnson, C. J.; Lapi, S. E.; Chapman, K. W.; Boros, E. Homologous Structural, Chemical, and Biological Behavior of Sc and Lu Complexes of the Picaga Bifunctional Chelator: Toward Development of Matched Theranostic Pairs for Radiopharmaceutical Applications. Bioconjugate Chem. 2021, 32 (7), 1232– 1241, DOI: 10.1021/acs.bioconjchem.0c00574
  51
  Homologous Structural, Chemical, and Biological Behavior of Sc and Lu Complexes of the Picaga Bifunctional Chelator: Toward Development of Matched Theranostic Pairs for Radiopharmaceutical Applications
  Vaughn, Brett A.; Koller, Angus J.; Chen, Zhihengyu; Ahn, Shin Hye; Loveless, C. Shaun; Cingoranelli, Shelbie J.; Yang, Yi; Cirri, Anthony; Johnson, Christopher J.; Lapi, Suzanne E.; Chapman, Karena W.; Boros, Eszter
  Bioconjugate Chemistry (2021), 32 (7), 1232-1241CODEN: BCCHES; ISSN:1043-1802. (American Chemical Society)
  The radioactive isotopes scandium-44/47 and lutetium-177 are gaining relevance for radioimaging and radiotherapy, resulting in a surge of studies on their coordination chem. and subsequent applications. Although the trivalent ions of these elements are considered close homologues, dissimilar chem. behavior is obsd. when they are complexed by large ligand architectures due to discrepancies between Lu(III) and Sc(III) ions with respect to size, chem. hardness, and Lewis acidity. Here, authors demonstrate that Lu and Sc complexes of 1,4-bis(methoxycarbonyl)-7-[(6-carboxypyridin-2-yl)methyl]-1,4,7-triazacyclononane (H3mpatcn) and its corresponding bioconjugate picaga-DUPA can be employed to promote analogous structural features and, subsequently, biol. properties for coordination complexes of these ions. The close homol. was evidenced using potentiometric methods, computational modeling, variable temp. mass spectrometry, and pair distribution function anal. of x-ray scattering data. Radiochem. labeling, in vitro stability, and biodistribution studies with Sc-47 and Lu-177 indicate that the 7-coordinate ligand environment of the bifunctional picaga ligand is compatible with biol. applications and the future investigation of β-emitting, picaga-chelated Sc and Lu isotopes for radiotherapy.
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52. 52
  Caravan, P.; Ellison, J. J.; McMurry, T. J.; Lauffer, R. B. Gadolinium(III) Chelates as MRI Contrast Agents: Structure, Dynamics, and Applications. Chem. Rev. 1999, 99 (9), 2293– 2352, DOI: 10.1021/cr980440x
  52
  Gadolinium(III) Chelates as MRI Contrast Agents: Structure, Dynamics, and Applications
  Caravan, Peter; Ellison, Jeffrey J.; McMurry, Thomas J.; Lauffer, Randall B.
  Chemical Reviews (Washington, D. C.) (1999), 99 (9), 2293-2352CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
  A review with 343 refs. on gadolinium(III) chelates judged to be of sufficient stability for in vivo use. Topics covered include soln. and solid state structures, relaxation theory, phys. properties, and macromol. conjugates.
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53. 53
  Le Fur, M.; Molnár, E.; Beyler, M.; Kálmán, F. K.; Fougère, O.; Esteban-Gómez, D.; Rousseaux, O.; Tripier, R.; Tircsó, G.; Platas-Iglesias, C. A Coordination Chemistry Approach to Fine-Tune the Physicochemical Parameters of Lanthanide Complexes Relevant to Medical Applications. Chem. – Eur. J. 2018, 24 (13), 3127– 3131, DOI: 10.1002/chem.201705528
  53
  A Coordination Chemistry Approach to Fine-Tune the Physicochemical Parameters of Lanthanide Complexes Relevant to Medical Applications
  Le Fur, Mariane; Molnar, Eniko; Beyler, Maryline; Kalman, Ferenc K.; Fougere, Olivier; Esteban-Gomez, David; Rousseaux, Olivier; Tripier, Raphael; Tircso, Gyula; Platas-Iglesias, Carlos
  Chemistry - A European Journal (2018), 24 (13), 3127-3131CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)
  The geometric features of two pyclen-based ligands possessing identical donor atoms but different site organization have a profound impact in their complexation properties toward lanthanide ions. The ligand contg. two acetate groups and a picolinate arm arranged in a sym. fashion (L1) forms a Gd3+ complex being two orders of magnitude less stable than its dissym. analog GdL2. Besides, GdL1 experiences a much faster dissocn. following the acid-catalyzed mechanism than GdL2. On the contrary, GdL1 exhibits a lower exchange rate of the coordinated water mol. compared to GdL2. These very different properties are related to different strengths of the Gd-ligand bonds assocd. to steric effects, which hinder the coordination of a water mol. in GdL2 and the binding of acetate groups in GdL1.
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54. 54
  Roca-Sabio, A.; Regueiro-Figueroa, M.; Esteban-Gómez, D.; de Blas, A.; Rodríguez-Blas, T.; Platas-Iglesias, C. Density Functional Dependence of Molecular Geometries in Lanthanide(III) Complexes Relevant to Bioanalytical and Biomedical Applications. Comput. Theor. Chem. 2012, 999, 93– 104, DOI: 10.1016/j.comptc.2012.08.020
  54
  Density functional dependence of molecular geometries in lanthanide(III) complexes relevant to bioanalytical and biomedical applications
  Roca-Sabio, Adrian; Regueiro-Figueroa, Martin; Esteban-Gomez, David; de Blas, Andres; Rodriguez-Blas, Teresa; Platas-Iglesias, Carlos
  Computational & Theoretical Chemistry (2012), 999 (), 93-104CODEN: CTCOA5; ISSN:2210-271X. (Elsevier B.V.)
  A set of 15 lanthanide-contg. model systems was used to evaluate the performance of 15 commonly available d. functionals (SVWN, SPL, BLYP, G96LYP, mPWLYP, B3LYP, BH&HLYP, B3PW91, BB95, mPWB95, TPSS, TPSSh, M06, CAM-B3LYP and wB97XD) in geometry detn., benchmarked against MP2 calcns. The best agreement between DFT optimized geometries and those obtained from MP2 calcns. is provided by meta-GGA and hybrid meta-GGA functionals. The use of hybrid-GGA functionals such as BH&HLYP and B3PW91 also provide reasonably good results, while B3LYP provides an important overestimation of the metal-ligand bonds. The performance of different basis sets to describe the ligand(s) atoms, as well as the use of large-core (LC) RECPs and small-core (SC) RECPs, has been also assessed. Our calcns. show that SCRECP calcns. provide somewhat shorter GdIII-donor distances than the LCRECP approach, the av. contraction of bond distances for the systems investigated amounting to 0.033 Å. However, geometry optimizations with the SCRECP (in combination with the mPWB95 functional and the 6-31G(d) basis set for the ligand atoms) take about 15 times longer than the LC counterparts, and about four times longer than MP2/LCRECP/6-31G(d) calcns. The 6-31G(d), 6-311G(d), 6-311G(d,p) or cc-pVDZ basis sets, in combination with LCRECPs, appear to offer an adequate balance between accuracy and computational cost for the description of mol. geometries of LnIII complexes. Electronic energies calcd. with the the cc-pVxZ family (x = D-6) indicate a relative fast convergence to the complete basis set (CBS) limit with basis set size. The inclusion of bulk solvent effects (IEFPCM) was shown to provoke an important impact on the calcd. geometries, particularly on the metal-nitrogen distances. Calcns. performed on lanthanide complexes relevant for practical applications confirmed the important effect of the solvent on the calcd. geometries.
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55. 55
  Inoue, M. B.; Inoue, M.; Muñoz, I. C.; Bruck, M. A.; Fernando, Q. Syntheses of New 15-Membered and 16-Membered Macrocyclic Ligands with Three Pendant Acetato Groups and the Structures of the Gadolinium(III) Complexes. Inorg. Chim. Acta 1993, 209, 29– 34, DOI: 10.1016/S0020-1693(00)84976-2
  55
  Syntheses of new 15-membered and 16-membered macrocyclic ligands with three pendant acetato groups and the structures of the gadolinium(III) complexes
  Inoue, Michiko B.; Inoue, Motomichi; Munoz, Iliana C.; Bruck, Michael A.; Fernando, Quintus
  Inorganica Chimica Acta (1993), 209 (1), 29-34CODEN: ICHAA3; ISSN:0020-1693.
  A condensation of diethylenetriaminepentaacetic dianhydride with ethylenediamine gave a 15-membered macrocyclic ligand with 3 pendant acetato groups, (15-dtpa-en)H3 = C10H18N5O2(CH2CO2H)3; a 16-membered analog, (16-dtpa-pn)H3 = C11H20N5O2(CH2CO2H)3, was obtained using 1,3-propanediamine instead of ethylenediamine. The structures of their Gd(III) complexes, Gd2(15-dtpa-en)2.16H2O and Gd(16-dtpa-pn).4H2O, were detd. by x-ray analyses. Gd2(15-dtpa-en)2.16H2O crystd. as orthorhombic, space group Pbca, a 18.205(1), b 18.930(1), c 15.609(1) Å, Z = 4, R = 0.026, Rw = 0.042. Two Gd(III) ions are located between 2 ligand mols., forming a binuclear metal chelate mol. with a center of inversion. The coordination geometry around a metal ion is described as a distorted tricapped trigonal prism that consists of 9 coordinated atoms. Gd(16-dtpa-pn).4H2O crystd. as monoclinic, space group P21/c, a 8.246(2), b 14.995(3), c 19.367(4) Å, β 90.258(2)°, Z = 4, R = 0.021, Rw = 0.035. In this compd., a H2O mol. and a single ligand mol. are coordinated to a Gd(III), forming a mononuclear chelate with a tricapped trigonal prism. The structural differences between the 2 Gd(III) complexes are a result of the differences in the favorable conformations assumed by the 2 macrocyclic ligands.
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56. 56
  Bader, R. F. W.; Carroll, M. T.; Cheeseman, J. R.; Chang, C. Properties of Atoms in Molecules: Atomic Volumes. J. Am. Chem. Soc. 1987, 109 (26), 7968– 7979, DOI: 10.1021/ja00260a006
  56
  Properties of atoms in molecules: atomic volumes
  Bader, Richard F. W.; Carroll, Marshall T.; Cheeseman, James R.; Chang, Cheng
  Journal of the American Chemical Society (1987), 109 (26), 7968-79CODEN: JACSAT; ISSN:0002-7863.
  The theory of atoms in mols. defines an atom and the av. values of its properties. The intersection of an at. surface, as defined by a property of the charge d., with a particular envelope of the charge d. defines the vol. of an atom in a mol. The value of the d. envelope used to bound the open portion of an at. region can be chosen on the basis of comparison with measured properties. The nature of the results are, in any event, independent of the choice for envelopes which contain >96% of the total electronic charge and lie within the usual range of van der Waals contact distances. It is shown that the vols. of Me and methylene groups in normal hydrocarbons are transferable properties, as are their charge distributions, populations, and energies. The vol. of a C atom subject to steric crowding decreases as its stability and electron population increase. This behavior is opposite to that found for a C atom in a system with geometric strain as found in cyclic and bicyclic mols. The stability, population, and vol. of a C atom all undergo parallel increases as the atom is subjected to an increasing degree of geometric strain. The vols. of the bridgehead C atoms in bicyclo[1.1.0]butane and [1.1.1]propellane are 1.2 and 1.5 times, resp., the vol. of a Me C atom. As anticipated on the basis of the orbital model, an increase in geometric strain is correlated with an increase in s character and thus finds the electron population, stability, and vol. of a C atom to undergo the same parallel increases in value through the series ethane, ethylene, acetylene. As a first step in the investigation of how atoms fit together, the changes in the at. vols. accompanying the formation of a H bond are detd.
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57. 57
  Neese, F. The ORCA Program System. WIREs Comput. Mol. Sci. 2012, 2 (1), 73– 78, DOI: 10.1002/wcms.81
  57
  The ORCA program system
  Neese, Frank
  Wiley Interdisciplinary Reviews: Computational Molecular Science (2012), 2 (1), 73-78CODEN: WIRCAH; ISSN:1759-0884. (Wiley-Blackwell)
  A review. ORCA is a general-purpose quantum chem. program package that features virtually all modern electronic structure methods (d. functional theory, many-body perturbation and coupled cluster theories, and multireference and semiempirical methods). It is designed with the aim of generality, extendibility, efficiency, and user friendliness. Its main field of application is larger mols., transition metal complexes, and their spectroscopic properties. ORCA uses std. Gaussian basis functions and is fully parallelized. The article provides an overview of its current possibilities and documents its efficiency.
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58. 58
  Neese, F. Software Update: The ORCA Program System, Version 4.0. WIREs Comput. Mol. Sci. 2018, 8 (1), e1327 DOI: 10.1002/wcms.1327
  There is no corresponding record for this reference.
59. 59
  Reiher, M. Douglas–Kroll–Hess Theory: A Relativistic Electrons-Only Theory for Chemistry. Theor. Chem. Acc. 2006, 116 (1–3), 241– 252, DOI: 10.1007/s00214-005-0003-2
  59
  Douglas-Kroll-Hess Theory: A relativistic electrons-only theory for chemistry
  Reiher, Markus
  Theoretical Chemistry Accounts (2006), 116 (1-3), 241-252CODEN: TCACFW; ISSN:1432-881X. (Springer GmbH)
  A review. A unitary transformation allows to sep. (block-diagonalize) the Dirac Hamiltonian into two parts one part: solely describes electrons, while the other gives rise to neg.-energy states, which are the so-called positronic states. The block-diagonal form of the Hamiltonian no longer accounts for the coupling of both kinds of states. The pos.-energy ('electrons-only') part can serve as a 'fully' relativistic electrons-only theory, which can be understood as a rigorous basis for chem. Recent developments of the Douglas-Kroll-Hess (DKH) method allowed to derive a sequence of expressions, which approx. this electrons-only Hamiltonian up to arbitrary-order. While all previous work focused on the numerical stability and accuracy of these arbitrary-order DKH Hamiltonians, conceptual issues and paradoxa of the method were mostly left aside. In this work, the conceptual side of DKH theory is revisited in order to identify essential aspects of the theory to be distinguished from purely computational consideration.
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60. 60
  Chai, J.-D.; Head-Gordon, M. Long-Range Corrected Hybrid Density Functionals with Damped Atom–Atom Dispersion Corrections. Phys. Chem. Chem. Phys. 2008, 10 (44), 6615– 6620, DOI: 10.1039/b810189b
  60
  Long-range corrected hybrid density functionals with damped atom-atom dispersion corrections
  Chai, Jeng-Da; Head-Gordon, Martin
  Physical Chemistry Chemical Physics (2008), 10 (44), 6615-6620CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
  We report re-optimization of a recently proposed long-range cor. (LC) hybrid d. functional [J.-D. Chai and M. Head-Gordon, J. Chem. Phys., 2008, 128, 084106] to include empirical atom-atom dispersion corrections. The resulting functional, ωB97X-D yields satisfactory accuracy for thermochem., kinetics, and non-covalent interactions. Tests show that for non-covalent systems, ωB97X-D shows slight improvement over other empirical dispersion-cor. d. functionals, while for covalent systems and kinetics it performs noticeably better. Relative to our previous functionals, such as ωB97X, the new functional is significantly superior for non-bonded interactions, and very similar in performance for bonded interactions.
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61. 61
  Chai, J.-D.; Head-Gordon, M. Systematic Optimization of Long-Range Corrected Hybrid Density Functionals. J. Chem. Phys. 2008, 128 (8), 084106 DOI: 10.1063/1.2834918
  61
  Systematic optimization of long-range corrected hybrid density functionals
  Chai, Jeng-Da; Head-Gordon, Martin
  Journal of Chemical Physics (2008), 128 (8), 084106/1-084106/15CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)
  A general scheme for systematically modeling long-range cor. (LC) hybrid d. functionals is proposed. Our resulting two LC hybrid functionals are shown to be accurate in thermochem., kinetics, and noncovalent interactions, when compared with common hybrid d. functionals. The qual. failures of the commonly used hybrid d. functionals in some "difficult problems," such as dissocn. of sym. radical cations and long-range charge-transfer excitations, are significantly reduced by the present LC hybrid d. functionals. (c) 2008 American Institute of Physics.
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62. 62
  Najibi, A.; Goerigk, L. The Nonlocal Kernel in van Der Waals Density Functionals as an Additive Correction: An Extensive Analysis with Special Emphasis on the B97M-V and ωB97M-V Approaches. J. Chem. Theory Comput. 2018, 14 (11), 5725– 5738, DOI: 10.1021/acs.jctc.8b00842
  62
  The Nonlocal Kernel in van der Waals Density Functionals as an Additive Correction: An Extensive Analysis with Special Emphasis on the B97M-V and ωB97M-V Approaches
  Najibi, Asim; Goerigk, Lars
  Journal of Chemical Theory and Computation (2018), 14 (11), 5725-5738CODEN: JCTCCE; ISSN:1549-9618. (American Chemical Society)
  The development of van der Waals d. functional approxns. (vdW-DFAs) has gained considerable interest over the past decade. While in a strictest sense, energy calcns. with vdW-DFAs should be carried out fully self-consistently, we demonstrate conclusively for a total of 11 methods that such a strategy only increases the computational time effort without having any significant effect on energetic properties, electron densities, or orbital-energy differences. The strategy to apply a nonlocal vdW-DFA kernel as an additive correction to a fully converged conventional DFA result is therefore justified and more efficient. As part of our study, we utilize the extensive GMTKN55 database for general main-group thermochem., kinetics, and noncovalent interactions [Phys. Chem. Chem. Phys.2017, 19, 32184], which allows us to analyze the very promising B97M-V [J. Chem. Phys. 2015, 142, 074111] and ωB97M-V [J. Chem. Phys. 2016, 144, 214110] DFAs. We also present new DFT-D3(BJ) based counterparts of these two methods and of ωB97X-V [J. Chem. Theory Comput 2013, 9, 263], which are faster variants with similar accuracy. Our study concludes with updated recommendations for the general method user, based on our current overview of 325 dispersion-cor. and -uncorrected DFA variants analyzed for GMTKN55. VdW-DFAs are the best representatives of the three highest rungs of Jacob's Ladder, namely, B97M-V, ωB97M-V, and DSD-PBEP86-NL.
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63. 63
  Weigend, F.; Ahlrichs, R. Balanced Basis Sets of Split Valence, Triple Zeta Valence and Quadruple Zeta Valence Quality for H to Rn: Design and Assessment of Accuracy. Phys. Chem. Chem. Phys. 2005, 7 (18), 3297– 3305, DOI: 10.1039/b508541a
  63
  Balanced basis sets of split valence, triple zeta valence and quadruple zeta valence quality for H to Rn: Design and assessment of accuracy
  Weigend, Florian; Ahlrichs, Reinhart
  Physical Chemistry Chemical Physics (2005), 7 (18), 3297-3305CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
  Gaussian basis sets of quadruple zeta valence quality for Rb-Rn are presented, as well as bases of split valence and triple zeta valence quality for H-Rn. The latter were obtained by (partly) modifying bases developed previously. A large set of more than 300 mols. representing (nearly) all elements-except lanthanides-in their common oxidn. states was used to assess the quality of the bases all across the periodic table. Quantities investigated were atomization energies, dipole moments and structure parameters for Hartree-Fock, d. functional theory and correlated methods, for which we had chosen Moller-Plesset perturbation theory as an example. Finally recommendations are given which type of basis set is used best for a certain level of theory and a desired quality of results.
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  https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2MXpsFWgu7o%253D&md5=a820fb6055c993b50c405ba0fc62b194
64. 64
  Pantazis, D. A.; Neese, F. All-Electron Scalar Relativistic Basis Sets for the Lanthanides. J. Chem. Theor. Comput. 2009, 5 (9), 2229– 2238, DOI: 10.1021/ct900090f
  64
  All-electron scalar relativistic basis sets for the lanthanides
  Pantazis, Dimitrios A.; Neese, Frank
  Journal of Chemical Theory and Computation (2009), 5 (9), 2229-2238CODEN: JCTCCE; ISSN:1549-9618. (American Chemical Society)
  Segmented all-electron relativistically contracted (SARC) basis sets are constructed for the elements 57La-71Lu and optimized for d. functional theory (DFT) applications. The basis sets are intended for use in combination with the DKH2 or ZORA scalar relativistic Hamiltonians for which individually optimized contractions are provided. Significant computational advantages can be realized owing to the loose contraction of the SARC basis sets compared to generally contracted basis sets, while their compact size allows them to replace effective core potentials for routine studies of lanthanide complexes. The new basis sets are evaluated in DFT calcns. of the first four ionization energies of the lanthanides. They yield results that accurately reproduce the exptl. trends, confirming a balanced treatment of different electronic configurations. The performance of the basis sets is further assessed in mol. systems with a comprehensive study of the lanthanide trihalides. Despite their compact size, the SARC basis sets demonstrate consistent, efficient, and reliable performance and will be esp. useful in calcns. of mol. properties that require explicit treatment of the core electrons.
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65. 65
  Bader, R. F. W. Atoms in Molecules. Acc. Chem. Res. 1985, 18, 9– 15, DOI: 10.1021/ar00109a003
  65
  Atoms in molecules
  Bader, R. F. W.
  Accounts of Chemical Research (1985), 18 (1), 9-15CODEN: ACHRE4; ISSN:0001-4842.
  A review with 21 refs.
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66. 66
  Tosi, M. P.; Fumi, F. G. Ionic Sizes And Born Repulsive Parameters In The NaCl-Type Alkali Halides-II: The Generalized Huggins-Mayer Form. J. Phys. Chem. Solids 1964, 25, 45– 52, DOI: 10.1016/0022-3697(64)90160-X
  66
  Ionic sizes and Born repulsive parameters in the NaCl-type alkali halides. II. Generalized Huggins-Mayer forms
  Tosi, M. P.; Fumi, F. G.
  Journal of Physics and Chemistry of Solids (1964), 25 (1), 45-52CODEN: JPCSAW; ISSN:0022-3697.
  The procedure described for the detn. of the crystal radii of the ions in the individual NaCl-type alkali halides from solid-state data by the Born model is applied, adopting a generalized Huggins-Mayer form for the Born repulsive energy (i.e. allowing the hardness parameter to vary from salt to salt). The resulting values of the crystal radii agree within 0.05 A. with the values obtained with the Huggins-Mayer and Pauling forms. This indicates that the Born model, irrespective of the specific plausible form adopted for the Born repulsive energy, leads to relative values of the crystal radii for the alkali and halogen ions in the NaCl structure exceeding by ∼0.3 A. the traditional relative values, which refer to nearly free ions. Qual. and quant. evidence supporting these ionic deformations is discussed.
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67. 67
  Pauling, L. The Sizes of Ions and the Structure of Ionic Crystals. J. Am. Chem. Soc. 1927, 49 (3), 765– 790, DOI: 10.1021/ja01402a019
  67
  Sizes of ions and structure of ionic crystals
  Pauling, Linus
  Journal of the American Chemical Society (1927), 49 (), 765-92CODEN: JACSAT; ISSN:0002-7863.
  With an at. model derived from the wave mechanics of Schr.ovrddot.odinger, size-screening consts. have been calcd. for the electrons in many-electron atoms and ions. After a discussion of the forces between ions, and of the significance of ionic sizes, values of the univalent crystal radius and the crystal radius are derived for a large no. of ions with the aid of these screening consts., using as a starting point the observed inter-atomic distances in crystals of NaF, KCl, RbBr, CsI and Li2O. The theoretical result is derived that ionic compds. MX2 will crystallize with fluorite structure if the radius ratio RM/RX is greater than 0.65, and with the rutile (or anatase) structure if it is less. This result is exptly. substantiated. Theoretically a binary compd. should have the sphalerite or wurzite structure instead of the NaCl structure if the radius ratio is less than 0.33. The oxide, sulfide, selenide and telluride of Be conform to this requirement, and are to be considered as ionic crystals. It is found, however, that such "tetrahedral" crystals are particularly apt to Show deformation, and it is suggested that this is a tendency of the anion to share an electron pair. with each cation.
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68. 68
  Lu, T.; Chen, F. Multiwfn: A Multifunctional Wavefunction Analyzer. J. Comput. Chem. 2012, 33 (5), 580– 592, DOI: 10.1002/jcc.22885
  68
  Multiwfn: A multifunctional wavefunction analyzer
  Lu, Tian; Chen, Feiwu
  Journal of Computational Chemistry (2012), 33 (5), 580-592CODEN: JCCHDD; ISSN:0192-8651. (John Wiley & Sons, Inc.)
  Multiwfn is a multifunctional program for wavefunction anal. Its main functions are: (1) Calcg. and visualizing real space function, such as electrostatic potential and electron localization function at point, in a line, in a plane or in a spatial scope. (2) Population anal. (3) Bond order anal. (4) Orbital compn. anal. (5) Plot d.-of-states and spectrum. (6) Topol. anal. for electron d. Some other useful utilities involved in quantum chem. studies are also provided. The built-in graph module enables the results of wavefunction anal. to be plotted directly or exported to high-quality graphic file. The program interface is very user-friendly and suitable for both research and teaching purpose. The code of Multiwfn is substantially optimized and parallelized. Its efficiency is demonstrated to be significantly higher than related programs with the same functions. Five practical examples involving a wide variety of systems and anal. methods are given to illustrate the usefulness of Multiwfn. The program is free of charge and open-source. Its precompiled file and source codes are available from http://multiwfn.codeplex.com. © 2011 Wiley Periodicals, Inc. J Comput Chem, 2011.
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69. 69
  Wada, A.; Watanabe, M.; Yamanoi, Y.; Nishihara, H. Modification of the Luminescence Spectra of Chloro(Tetrapyridylcyclotetramine)Europium Complexes by Fine Tuning of the Eu–Cl Distance with Outer-Sphere Counterions in the Solid State, in a Polymer Matrix and in Solution. Chem. Commun. 2008, 1671– 1673, DOI: 10.1039/b716987f
  69
  Modification of the luminescence spectra of chloro(tetrapyridylcyclotetramine)europium complexes by fine tuning of the Eu-Cl distance with outer-sphere counterions in the solid state, in a polymer matrix and in solution
  Wada, Atsushi; Watanabe, Masayuki; Yamanoi, Yoshinori; Nishihara, Hiroshi
  Chemical Communications (Cambridge, United Kingdom) (2008), (14), 1671-1673CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
  Controlling the coordination environments and the luminescence of Eu3+ complexes with outer-sphere counterions was achieved in the solid state, in a polymer matrix and in soln.
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70. 70
  Natrajan, L. S.; Khoabane, N. M.; Dadds, B. L.; Muryn, C. A.; Pritchard, R. G.; Heath, S. L.; Kenwright, A. M.; Kuprov, I.; Faulkner, S. Probing the Structure, Conformation, and Stereochemical Exchange in a Family of Lanthanide Complexes Derived from Tetrapyridyl-Appended Cyclen. Inorg. Chem. 2010, 49 (17), 7700– 7709, DOI: 10.1021/ic100447m
  70
  Probing the Structure, Conformation, and Stereochemical Exchange in a Family of Lanthanide Complexes Derived from Tetrapyridyl-Appended Cyclen
  Natrajan, Louise S.; Khoabane, Ntai M.; Dadds, Benjamin L.; Muryn, Christopher A.; Pritchard, Robin G.; Heath, Sarah L.; Kenwright, Alan M.; Kuprov, Ilya; Faulkner, Stephen
  Inorganic Chemistry (2010), 49 (17), 7700-7709CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
  A series of lanthanide complexes have been synthesized from 1,4,7,10-tetrakis(2-pyridylmethyl)-1,4,7,10-tetraazacyclododecane (LPy). Crystallog. studies indicate that, in the solid phase, all of the lanthanide ions are 9-coordinate and are bound to eight N atoms from the donor ligand, with the ninth site being filled by a counterion or solvent mol. In soln., time-resolved luminescence studies indicate that the luminescence exhibits contributions from two species corresponding to the nonhydrated and hydrated forms. The NMR spectra in protic media show two dominant isomers on the NMR time scale; furthermore, the spectra are very different from those obtained for 1,4,7,10-tetraazacyclododecane-N',N'',N''',N''''-tetraacetic acid (DOTA) and its derivs. The different forms of the complex undergo slow conformational and enantiomeric exchange in soln., which has been measured by NMR. The exchange path has been mapped out by d. functional theory calcns. and shows multiple metastable conformations (with respect to the dihedral angles of the cyclen ring). This contrasts with the established NMR behavior of DOTA complexes, which has been described by a two-state soln. equil.
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71. 71
  Gunnlaugsson, T.; Davies, R. J. H.; Kruger, P. E.; Jensen, P.; McCabe, T.; Mulready, S.; O’Brien, J. E.; Stevenson, C. S.; Fanning, A.-M. Cyclen Based Lanthanide Ion Ribonuclease Mimics: The Effect of Pyridine Cofactors upon Phosphodiester HPNP Hydrolysis. Tetrahedron Lett. 2005, 46 (21), 3761– 3766, DOI: 10.1016/j.tetlet.2005.03.150
  71
  Cyclen based lanthanide ion ribonuclease mimics: the effect of pyridine cofactors upon phosphodiester HPNP hydrolysis
  Gunnlaugsson, Thorfinnur; Davies, R. Jeremy H.; Kruger, Paul E.; Jensen, Paul; McCabe, Thomas; Mulready, Sinead; O'Brien, John E.; Stevenson, Clarke S.; Fanning, Ann-Marie
  Tetrahedron Letters (2005), 46 (21), 3761-3766CODEN: TELEAY; ISSN:0040-4039. (Elsevier B.V.)
  The cyclen based pyridine complexes 1Ln-3Ln (Ln = La(III) and Eu(III); 1-3 = N-(pyridin-x-yl)-2-[2,7,10-tris[(pyridin-x-ylcarbamoyl)methyl]-1,4,7,10-tetraazacyclododec-1-yl]acetamide (x = 2, 3, 4)) were synthesized as metallo-RNase mimics and their ability to hydrolytically cleave the phosphodiester of HPNP ((p-O2NC6H4O)(HOCHMeCH2O)PO2-) at 37° was studied using UV-visible spectroscopy, whereas the binding of the substrate was evaluated using 31P NMR and Eu(III)-luminescent measurements. In contrast 2Ln gave rise to fast pH dependent hydrolysis of HPNP, with max. efficiency at pH ∼8.2, and with a half-life of ∼1 h, the 1Ln and 3Ln complexes are inactive, emphasizing the importance of the nature of the pyridine isomer as a cofactor in the hydrolytic process. The crystal and mol. structures of the La, Eu and Gd complexes with the pyridin-3-yl-derived macrocycle were detd. by x-ray crystallog.
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72. 72
  Gao, J.; Ye, K.; He, M.; Xiong, W.-W.; Cao, W.; Lee, Z. Y.; Wang, Y.; Wu, T.; Huo, F.; Liu, X.; Zhang, Q. Tuning Metal–Carboxylate Coordination in Crystalline Metal–Organic Frameworks through Surfactant Media. J. Solid State Chem. 2013, 206, 27– 31, DOI: 10.1016/j.jssc.2013.07.031
  72
  Tuning metal-carboxylate coordination in crystalline metal-organic frameworks through surfactant media
  Gao, Junkuo; Ye, Kaiqi; He, Mi; Xiong, Wei-Wei; Cao, Wenfang; Lee, Zhi Yi; Wang, Yue; Wu, Tom; Huo, Fengwei; Liu, Xiaogang; Zhang, Qichun
  Journal of Solid State Chemistry (2013), 206 (), 27-31CODEN: JSSCBI; ISSN:0022-4596. (Elsevier B.V.)
  Although it was widely demonstrated that surfactants can efficiently control the size, shape and surface properties of micro/nanocrystals of metal-org. frameworks (MOFs) due to the strong interactions between surfactants and crystal facets of MOFs, the use of surfactants as reaction media to grow MOF single crystals is unprecedented. Compared with ionic liqs., surfactants are much cheaper and can have multifunctional properties such as acidic, basic, neutral, cationic, anionic, or even block. These factors strongly motivate the authors to develop a new synthetic strategy: growing cryst. MOFs in surfactants. Eight new two-dimensional (2D) or three-dimensional (3D) MOFs were successfully synthesized in an industrially-abundant and environmentally-friendly surfactant: polyethylene glycol-200 (PEG-200). Eight different coordination modes of carboxylates, ranging from monodentate η1 mode to tetra-donor coordination μ3-η1:η2:η1 mode, were founded in the authors' research. The magnetic properties of Co-based MOFs were studied and MOF NTU-Z6b showed a phase transition with a Curie temp. (Tc) at 5 K. The authors' strategy of growing cryst. MOFs in surfactant could offer exciting opportunities for prepg. novel MOFs with diverse structures and interesting properties.
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73. 73
  Gao, S.; George, S. J.; Zhou, Z.-H. Interaction of Gd-DTPA with Phosphate and Phosphite: Toward the Reaction Intermediate in Nephrogenic Systemic Fibrosis. Dalton Trans. 2016, 45 (12), 5388– 5394, DOI: 10.1039/C5DT04172D
  73
  Interaction of Gd-DTPA with phosphate and phosphite: toward the reaction intermediate in nephrogenic systemic fibrosis
  Gao, Song; George, Simon J.; Zhou, Zhao-Hui
  Dalton Transactions (2016), 45 (12), 5388-5394CODEN: DTARAF; ISSN:1477-9226. (Royal Society of Chemistry)
  Direct reactions of the MRI contrast agent K2[Gd(DTPA)(H2O)]·5H2O (1) (H5DTPA = diethylenetriaminepentaacetic acid) with dipotassium hydrogen phosphate (K2HPO4) or phosphite (K2HPO3) result in the isolation of well-defined Gd-DTPA phosphite K6[Gd2(DTPA)2(HPO3)]·7H2O (2) or phosphate K6[Gd2(DTPA)2(HPO4)]·10H2O (3), resp. Their lanthanum analogs K4[La2(DTPA)2(H2O)]·8H2O (4), K6[La2(DTPA)2(HPO3)]·7H2O (5) and K6[La2(DTPA)2(HPO4)]·10H2O (6) are used for comparison. The phosphate and phosphite groups are able to substitute the coordinated water mols. in 1 and 4 in a close physiol. aq. soln., and act as bridging ligands to link adjacent Ln(DTPA)2- (Ln = Gd and La) into dimeric structures. Solid state and soln. 13C NMR spectra of dimer 4 show complete dissocn. into its monomeric species in soln., while no dissocn. is obsd. for lanthanum phosphite 5 and phosphate 6 in soln., which show only one set of 13C spectra with the largest downfield shifts at 182.0 and 182.3 ppm resp. Comparisons of the bond distances and spectral data indicate that the interaction between DTPA and central Ln3+ cations are weakened after the substitutions, which support phosphate substituted Gd-DTPA as an initial intermediate in nephrogenic systemic fibrosis.
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74. 74
  Onate, C. A.; Okon, I. B.; Vincent, U. E.; Eyube, E. S.; Onyeaju, M. C.; Omugbe, E.; Egharevba, G. O. Non-Relativistic Molecular Modified Shifted Morse Potential System. Sci. Rep. 2022, 12 (1), 15188, DOI: 10.1038/s41598-022-19179-4
  74
  Non-relativistic molecular modified shifted Morse potential system
  Onate, C. A.; Okon, I. B.; Vincent, U. E.; Eyube, E. S.; Onyeaju, M. C.; Omugbe, E.; Egharevba, G. O.
  Scientific Reports (2022), 12 (1), 15188CODEN: SRCEC3; ISSN:2045-2322. (Nature Portfolio)
  Abstr.: A shifted Morse potential model is modified to fit the study of the vibrational energies of some mols. Using a traditional technique/methodol., the vibrational energy and the un-normalized radial wave functions were calcd. for the modified shifted Morse potential model. The condition that fits the modified potential for mol. description were deduced together with the expression for the screening parameter. The vibrational energies of SiC, NbO, CP, PH, SiF, NH and Cs2 mols. were computed by inserting their resp. spectroscopic consts. into the calcd. energy equation. It was shown that the calcd. results for all the mols. agreement perfectly with the exptl. RKR values. The present potential performs better than Improved Morse and Morse potentials for cesium dimer. Finally, the real Morse potential model was obtained as a special case of the modified shifted potential.
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75. 75
  Janicki, R.; Mondry, A. Structural and Thermodynamic Aspects of Hydration of Gd(iii) Systems. Dalton Trans. 2019, 48, 3380– 3391, DOI: 10.1039/C8DT04869J
  75
  Structural and thermodynamic aspects of hydration of Gd(III) systems
  Janicki, Rafal; Mondry, Anna
  Dalton Transactions (2019), 48 (10), 3380-3391CODEN: DTARAF; ISSN:1477-9226. (Royal Society of Chemistry)
  X-ray crystal structures of Gd(III) and Lu(III) aqua ions as well as their complexes with polyaminopolycarboxylates (EDTA, CDTA, EGTA, DTPA, DOTA) were detd.: [Gd(H2O)9](CF3SO3)3, [Gd(H2O)8]Cl3·C10H20O5, [Lu(H2O)8]Cl3·C12H24O6·4H2O, [C(NH2)3][Gd(EDTA)(H2O)3], [C(NH2)3]2[Lu(EDTA)(H2O)2]ClO4·6H2O, [C(NH2)3][Lu(CDTA)(H2O)2]·6H2O, [C(NH2)3][Gd(EGTA)(H2O)]·2H2O, [C(NH2)2(N2H4)][Gd(HDTPA)(H2O)]·2H2O, Na[Gd(DOTA)(H2O)]·4H2O, and K2[Lu(DOTA)]Cl·4.6H2O. The weighted sums of UV absorption spectra of appropriate crystals were used to reproduce the spectra of the Gd(III) aq. solns. in the temp. range 276-363 K. In aq. soln. the Gd(III)-EGTA, Gd(III)-DTPA and Gd(III)-DOTA complexes exist as almost pure monohydrate [GdL(H2O)]n- species, while in the case of the Gd(III) aqua ion, Gd(III)-EDTA and Gd(III)-CDTA systems the equil. between variously hydrated species were found. The derived molar fractions of these species were used to det. the ΔG, ΔH and ΔS of hydration. These thermodn. functions may be derived not only from the spectra of the hypersensitive transitions, but from other f-f transitions as well. Next the ΔG, ΔH and ΔS values of hydration for the other Ln(III)-EDTA systems (Ln = Pr, Nd, Sm, Eu) were detd. The ΔG298 values of the dehydration reaction for Ln(III)-EDTA complexes (Ln = Pr, Nd, Sm, Eu, Gd, Ho, Er) were almost linearly dependent on the no. of 4f electrons in the whole series of lanthanides. Also, the point, where the ratio of [LnL(H2O)n] : [LnL(H2O)n-1] is 1, shifts along the lanthanide series depending on the ligand denticity - the higher the ligand denticity, the farther the point of the equimolar ratio in the lanthanide series. The presented results are the 1st systematic exptl. study on the thermodn. description of the hydration equil. of Gd(III) compds.
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76. 76
  Graeppi, N.; Hugh Powell, D.; Laurenczy, G.; Zékány, L.; Merbach, A. E. Coordination Equilibria and Water Exchange Kinetics of Lanthanide(III) Propylenediaminetetraacetates and Other Magnetic Resonance Imaging Related Complexes. Inorg. Chim. Acta 1995, 235 (1–2), 311– 326, DOI: 10.1016/0020-1693(95)90073-F
  76
  Coordination equilibria and water exchange kinetics of lanthanide(III) propylenediaminetetraacetates and other magnetic resonance imaging related complexes
  Graeppi, Nicole; Powell, D. Hugh; Laurenczy, Gabor; Zekany, Laszlo; Merbach, Andre E.
  Inorganica Chimica Acta (1995), 235 (1-2), 311-26CODEN: ICHAA3; ISSN:0020-1693. (Elsevier)
  The UV-Vis absorption spectra of aq. solns. of Eu3+ complexes with the hexadentate polyaminocarboxylate ligands EDTA4-, CDTA4-, HDTA3- and PDTA4- were measured as a function of temp. and pressure in the frequency region corresponding to the 7F0→5D0 transition of Eu3+. The results can be explained in terms of equil. between nine-coordinate and eight-coordinate species where the eight-coordinate species contain one less inner sphere water mol. than the nine-coordinate species. The thermodn. parameters, including the reaction vol., for these equil. were detd. 17O NMR transverse relaxation rates and chem. shifts were measured for aq. solns. of the eight-coordinate complexes [Ln(PDTA)(H2O)2]- (Ln = Tb, Dy, Er, Tm, Yb) and [Er(EDTA)(H2O)2]- as a function of temp., pressure and magnetic field. The results were analyzed in terms of the water exchange kinetics on the complexes. The water exchange rate on [Ln(PDTA)(H2O)2]- decreases dramatically with decreasing ionic radius across the lanthanide series from kex298 = (2.4±0.1)×107 s-1 for Ln = Tb to kex298 = (2.8±0.3)×105 s-1 for Ln = Yb. The activation vols. show that this is accompanied by a change of exchange mechanism from associatively activated for Ln = Tb (ΔV # = -7.6±0.3 cm3 mol-1) to dissociatively activated for Ln = Yb (ΔV # = +7.4±0.8 cm3 mol-1). Water exchange on [Er(EDTA)(H2O)2]- (kex298 = (9.8±1.9)×106 s-1) is more than an order of magnitude faster than on [Er(PDTA)(H2O)2]- (kex298 = (5.6±0.5)×105 s-1). These kinetic results can be interpreted in terms of the equil. measured by UV-Vis spectrophotometry. The implications of these observations for the design of new MRI contrast agents are discussed.
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77. 77
  Balogh, E.; Mato-Iglesias, M.; Platas-Iglesias, C.; Tóth, É.; Djanashvili, K.; Peters, J. A.; de Blas, A.; Rodríguez-Blas, T. Pyridine- and Phosphonate-Containing Ligands for Stable Ln Complexation. Extremely Fast Water Exchange on the Gd^III Chelates. Inorg. Chem. 2006, 45 (21), 8719– 8728, DOI: 10.1021/ic0604157
  77
  Pyridine- and Phosphonate-Containing Ligands for Stable Ln Complexation. Extremely Fast Water Exchange on the GdIII Chelates
  Balogh, Edina; Mato-Iglesias, Marta; Platas-Iglesias, Carlos; Toth, Eva; Djanashvili, Kristina; Peters, Joop A.; de Blas, Andres; Rodriguez-Blas, Teresa
  Inorganic Chemistry (2006), 45 (21), 8719-8728CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
  Two novel ligands contg. pyridine units and phosphonate pendant arms, with ethane-1,2-diamine (L2) or cyclohexane-1,2-diamine (L3) backbones, have been synthesized for Ln complexation. The hydration nos. obtained from luminescence lifetime measurements in aq. solns. of the EuIII and TbIII complexes are q = 0.6 (EuL2), 0.7 (TbL2), 0.8 (EuL3), and 0.4 (TbL3). To further assess the hydration equil., we have performed a variable-temp. and -pressure UV-vis spectrophotometric study on the EuIII complexes. The reaction enthalpy, entropy, and vol. for the hydration equil. EuL ↔ EuL(H2O) were calcd. to be ΔH° = -(11.6 ± 2) kJ mol-1, ΔS° = -(34.2 ± 5) J mol-1 K-1, and KEu298 = 1.8 ± 0.3 for EuL2 and ΔH° = -(13.5 ± 1) kJ mol-1, ΔS° = -(41 ± 4) J mol-1 K-1, and KEu298 = 1.7 ± 0.3 for EuL3, resp. Variable-temp. 17O NMR and nuclear magnetic relaxation dispersion (NMRD) were measured for GdL2(H2O)q and GdL3(H2O)q systems. Given the presence of phosphonate groups in the ligand backbone, a second-sphere relaxation mechanism has been included for the anal. of the longitudinal 17O and 1H NMR relaxation rates. The water exchange rate on GdL2(H2O)q, kex298 = (7.0 ± 0.8) × 108 s-1, is extremely high and comparable to that on the GdIII aqua ion, while it is slightly reduced for GdL3(H2O)q, kex298 = (1.5 ± 0.1) × 108 s-1. This fast exchange can be rationalized in terms of a very flexible inner coordination sphere, which is slightly rigidified for L3 by the introduction of the cyclohexyl group on the amine backbone. The water exchange proceeds via a dissociative interchange mechanism, evidenced by the pos. activation vols. obtained from variable-pressure 17O NMR for both GdL2(H2O)q and GdL3(H2O)q (ΔV⧧ = +8.3 ± 1.0 and 8.7 ± 1.0 cm3 mol-1, resp.).
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78. 78
  Janicki, R.; Mondry, A. A New Approach to Determination of Hydration Equilibria Constants for the Case of [Er(EDTA)(H₂O)_n ]⁻ Complexes. Phys. Chem. Chem. Phys. 2014, 16 (48), 26823– 26831, DOI: 10.1039/C4CP04093G
  78
  A new approach to determination of hydration equilibria constants for the case of [Er(EDTA)(H2O)n]- complexes
  Janicki, Rafal; Mondry, Anna
  Physical Chemistry Chemical Physics (2014), 16 (48), 26823-26831CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
  Two anionic complexes [Er(EDTA)(H2O)2]- and [Er(EDTA)(H2O)3]- were obtained as the following compds.: [C(NH2)3]2[Er(EDTA)(H2O)2]ClO4·6H2O (1) and Na[Er(EDTA)(H2O)3]·5H2O (2), resp. The UV-visible-NIR absorption spectra of both monocrystals were measured at room temp. and at 4.2 K. The influence of coordination no. on intensities of the f-f transitions and the crystal field splitting of 2S+1LJ multiplets are discussed. The weighted sum of molar absorptivities of f-f transitions in the spectra of 1 and 2 was used to reproduce the absorption bands of the Er3+-EDTA complex in aq. soln. This approach allowed the authors to est. that the complex in soln. exists in 95% as the 8-coordinate [Er(EDTA)(H2O)2]- species and in 5% as the 9-coordinate [Er(EDTA)(H2O)3]- ones as well as to calc. the conditional hydration equil. const. (Kaqua) of the reaction: [Er(EDTA)(H2O)3]- ↔ [Er(EDTA)(H2O)2]- + H2O which is rather difficult to det. by using other methods. The Kaqua value is 19 ± 1.
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79. 79
  Zhang, J.; Dolg, M. Labile Capping Bonds in Lanthanide(III) Complexes: Shorter and Weaker. J. Phys. Chem. A 2015, 119 (4), 774– 780, DOI: 10.1021/jp511043c
  79
  Labile Capping Bonds in Lanthanide(III) Complexes: Shorter and Weaker
  Zhang, Jun; Dolg, Michael
  Journal of Physical Chemistry A (2015), 119 (4), 774-780CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)
  For a wide range of trivalent lanthanide ion coordination complexes of tricapped trigonal prism or monocapped square antiprism configurations, the bonds between the central lanthanide ions and the capping ligands are found to violate Badger's rule: they can get weaker as they get shorter. We demonstrate that this observation originates from the screening and repulsion effect of the prism ligands. Both effects enhance as the elec. field of the central ion or the softness of the prism ligands increases. Thus, for heavier lanthanides, despite the fact that the capping bond could be shorter, it is more efficient to be weakened by the prism ligands, being inherently labile. This concept of "labile capping bonds phenomenon" is then successfully used to interpret many problems in lanthanide(III) hydration, e.g., why the water exchange rate of a lanthanide(III) complex is much higher in a twisted square antiprism than in square antiprism configuration. Thus, the theory proposed in this paper offers new insights in understanding chem. problems.
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80. 80
  Quici, S.; Marzanni, G.; Forni, A.; Accorsi, G.; Barigelletti, F. New Lanthanide Complexes for Sensitized Visible and Near-IR Light Emission: Synthesis, ¹H NMR, and X-Ray Structural Investigation and Photophysical Properties. Inorg. Chem. 2004, 43 (4), 1294– 1301, DOI: 10.1021/ic035143b
  80
  New Lanthanide Complexes for Sensitized Visible and Near-IR Light Emission: Synthesis, 1H NMR, and X-ray Structural Investigation and Photophysical Properties
  Quici, Silvio; Marzanni, Giovanni; Forni, Alessandra; Accorsi, Gianluca; Barigelletti, Francesco
  Inorganic Chemistry (2004), 43 (4), 1294-1301CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
  The authors describe the syntheses, the 1H NMR studies in CD3OD and D2O as solvent, the x-ray characterization, and the luminescence properties in D2O soln. of the two complexes EuL and ErL (H3L = I), in which the phenanthroline unit which plays the role of light antenna for the sensitization process of the metal centered luminescence. In a previous report (Inorg. Chem. 2002, 41, 2777), for EuL there are no H2O mols. within the 1st coordination sphere. X-ray and 1H NMR results reported here are consistent with full satn. of the nine coordination sites within the EuL and ErL complexes. These studies provide important details regarding the conformations, square antiprism (SAP) and twisted square antiprism (TSAP), adopted in soln. by these complexes. The luminescence results are consistent with both an effective intersystem crossing (ISC) at the light absorbing phenanthroline unit (λexc = 278 nm) and an effective energy transfer (en) process from the phenanthroline donor to the cation acceptor (with unit or close to unit efficiency for both steps). In D2O solvent, the overall sensitization efficiency, φse, is 0.3 and 5 × 10-6, for EuL (main luminescence peaks at 585, 612, 699 nm) and ErL (luminescence peak at 1530 nm), resp. The photophys. properties of both complexes are discussed with ref. to their structural features as elucidated by the obtained 1H NMR and x-ray results.
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81. 81
  Storm Thomsen, M.; Andersen, H. O. B.; So̷rensen, T. J. Long Story Short: Donor Set Symmetry in [Eu(DOTA)(H₂O)]⁻ Crystals Determines the Electronic Structure. Dalton Trans. 2022, 51 (37), 14118– 14124, DOI: 10.1039/D2DT02172B
  81
  Long story short: donor set symmetry in [Eu(DOTA)(H2O)]- crystals determines the electronic structure
  Storm Thomsen, Maria; Andersen, Helene Obel Boech; Soerensen, Thomas Just
  Dalton Transactions (2022), 51 (37), 14118-14124CODEN: DTARAF; ISSN:1477-9226. (Royal Society of Chemistry)
  Lanthanide complexes of 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid DOTA have been studied in great detail due to their use as MRI contrast agents. Since the first report from Desreux in 1980, the Ln[DOTA]- complexes of gadolinium(III) in particular have been thoroughly investigated. The forms of the nine-coordinated [Ln(DOTA)(H2O)]- complexes are well known, and the ligand backbone has been used extensively to create functional MRI contrast agents, luminescent probes, and as a model system for studying the properties of lanthanide(III) ions. In soln., the photophys. properties have been mapped, but as the structures are not known, direct structure-property relationships have not been created. Here, the electronic properties of two Eu[DOTA] compds. (1 and 2) and a Eu[DOTA]-like compd. (3) were studied using single-crystal luminescence spectroscopy. The donor set in the three compds. is identical (4N 4O 1O), and using the symmetry deviation value σ-ideal it was shown that the coordination geometry is close to identical. Nevertheless, the electronic properties evaluated using the luminescence spectrum were found to differ significantly between the three compds. The magnitude of the crystal field splitting was found not to scale with the symmetry of the coordination geometry. It was concluded that the donor set dictates the splitting, yet the structure-property relationships governing the electronic properties of europium(III) ions still elude us.
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82. 82
  Howard, J. A. K.; Kenwright, A. M.; Moloney, J. M.; Parker, D.; Woods, M.; Howard, J. A. K.; Port, M.; Navet, M.; Rousseau, O. Structure and Dynamics of All of the Stereoisomers of Europium Complexes of Tetra(Carboxyethyl) Derivatives of Dota: Ring Inversion Is Decoupled from Cooperative Arm Rotation in the RRRR and RRRS Isomers. Chem. Commun. 1998, 13, 1381– 1382, DOI: 10.1039/a802847h
  There is no corresponding record for this reference.
83. 83
  Janicki, R.; Mondry, A. Structural and Thermodynamic Aspects of Hydration of Gd(iii) Systems. Dalton Trans. 2019, 48 (10), 3380– 3391, DOI: 10.1039/C8DT04869J
  83
  Structural and thermodynamic aspects of hydration of Gd(III) systems
  Janicki, Rafal; Mondry, Anna
  Dalton Transactions (2019), 48 (10), 3380-3391CODEN: DTARAF; ISSN:1477-9226. (Royal Society of Chemistry)
  X-ray crystal structures of Gd(III) and Lu(III) aqua ions as well as their complexes with polyaminopolycarboxylates (EDTA, CDTA, EGTA, DTPA, DOTA) were detd.: [Gd(H2O)9](CF3SO3)3, [Gd(H2O)8]Cl3·C10H20O5, [Lu(H2O)8]Cl3·C12H24O6·4H2O, [C(NH2)3][Gd(EDTA)(H2O)3], [C(NH2)3]2[Lu(EDTA)(H2O)2]ClO4·6H2O, [C(NH2)3][Lu(CDTA)(H2O)2]·6H2O, [C(NH2)3][Gd(EGTA)(H2O)]·2H2O, [C(NH2)2(N2H4)][Gd(HDTPA)(H2O)]·2H2O, Na[Gd(DOTA)(H2O)]·4H2O, and K2[Lu(DOTA)]Cl·4.6H2O. The weighted sums of UV absorption spectra of appropriate crystals were used to reproduce the spectra of the Gd(III) aq. solns. in the temp. range 276-363 K. In aq. soln. the Gd(III)-EGTA, Gd(III)-DTPA and Gd(III)-DOTA complexes exist as almost pure monohydrate [GdL(H2O)]n- species, while in the case of the Gd(III) aqua ion, Gd(III)-EDTA and Gd(III)-CDTA systems the equil. between variously hydrated species were found. The derived molar fractions of these species were used to det. the ΔG, ΔH and ΔS of hydration. These thermodn. functions may be derived not only from the spectra of the hypersensitive transitions, but from other f-f transitions as well. Next the ΔG, ΔH and ΔS values of hydration for the other Ln(III)-EDTA systems (Ln = Pr, Nd, Sm, Eu) were detd. The ΔG298 values of the dehydration reaction for Ln(III)-EDTA complexes (Ln = Pr, Nd, Sm, Eu, Gd, Ho, Er) were almost linearly dependent on the no. of 4f electrons in the whole series of lanthanides. Also, the point, where the ratio of [LnL(H2O)n] : [LnL(H2O)n-1] is 1, shifts along the lanthanide series depending on the ligand denticity - the higher the ligand denticity, the farther the point of the equimolar ratio in the lanthanide series. The presented results are the 1st systematic exptl. study on the thermodn. description of the hydration equil. of Gd(III) compds.
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84. 84
  Kriemen, E.; Holzapfel, M.; Ruf, E.; Rehbein, J.; Maison, W. Synthesis and Structural Analysis of 1,4,7,10-Tetraazacyclododecane-1,4,7,10-tetraazidoethylacetic Acid (DOTAZA) Complexes. Eur. J. Inorg. Chem. 2015, 2015 (32), 5368– 5378, DOI: 10.1002/ejic.201500789
  84
  Synthesis and Structural Analysis of 1,4,7,10-Tetraazacyclododecane-1,4,7,10--tetraazidoethylacetic Acid (DOTAZA) Complexes
  Kriemen, Ella; Holzapfel, Malte; Ruf, Erik; Rehbein, Julia; Maison, Wolfgang
  European Journal of Inorganic Chemistry (2015), 2015 (32), 5368-5378CODEN: EJICFO; ISSN:1434-1948. (Wiley-VCH Verlag GmbH & Co. KGaA)
  Herein, the authors present the synthesis and structural anal. of metal complexes of enantiomerically pure 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraazidoethylacetic acid (DOTAZA, I). DOTAZA is a new tunable analog of DOTA, a clin. approved chelator for various pharmaceutically relevant metal ions. The authors study the complexation chem. of DOTAZA and report the crystal structures of a no. of complexes with pharmaceutically relevant metal ions such as Gd3+ [magnetic resonance imaging (MRI)], Eu3+ (luminescence spectroscopy), Y3+ [positron emission tomog. (PET)], In3+ [single-photon-emission computed tomog. (SPECT)], and Na+. These structures provide useful information for imaging applications and demonstrate the potential of DOTAZA to form stable complexes. Owing to its clickable azide functionalities, it may be used for the development of tailored imaging reagents that retain the pos. complexation chem. of the parent compd. DOTA.
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85. 85
  Siega, P.; Wuerges, J.; Arena, F.; Gianolio, E.; Fedosov, S. N.; Dreos, R.; Geremia, S.; Aime, S.; Randaccio, L. Release of Toxic Gd³⁺ Ions to Tumour Cells by Vitamin B₁₂ Bioconjugates. Chem. – Eur. J. 2009, 15 (32), 7980– 7989, DOI: 10.1002/chem.200802680
  85
  Release of Toxic Gd3+ Ions to Tumour Cells by Vitamin B12 Bioconjugates
  Siega, Patrizia; Wuerges, Jochen; Arena, Francesca; Gianolio, Eliana; Fedosov, Sergey N.; Dreos, Renata; Geremia, Silvano; Aime, Silvio; Randaccio, Lucio
  Chemistry - A European Journal (2009), 15 (32), 7980-7989, S7980/1-S7980/7CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)
  Two probes consisting of vitamin B12 (CNCbl) conjugated to Gd chelates by esterification of the ribose 5'-OH moiety, Gd-DTPA-CNCbl (1; DTPA= diethylenetriamine-N,N,N',N'',N''-pentaacetic acid) and Gd-TTHA-CNCbl (2; TTHA= triethylenetetramine-N,N,N',N'',N''',N'''-hexaacetic acid), have been synthesized and characterized. The crystal structure of a dimeric form of 1, obtained by crystn. with an excess of GdCl3, has been detd. The kinetics of binding to and dissocn. from transcobalamin II show that 1 and 2 maintain high-affinity binding to the vitamin B12 transport protein. Complex 2 is very stable with respect to Gd3+ release owing to the satd. co-ordination of the Gd3+ ion by four amino and five carboxylate groups. Hydrolysis of the ester functionality occurs on the time scale of several hours. The lack of satn. and the possible involvement of the ester functionality in co-ordination result in lower stability of 1 towards hydrolysis and in a considerable release of Gd3+ in vitro. Gd3+ ions released from 1 are avidly taken up by the K562 tumor cells to an extent corresponding to approx. 1010 Gd3+ per cell. The internalization of toxic Gd3+ ions causes a marked decrease in cell viability as assessed by Trypan blue and WST-1 tests. On the contrary, the expts. with the more stable 2 did not show any significant cell internalization of Gd3+ ions and any influence on cell viability. The results point to new avenues of in situ generation of cytotoxic pathways based on the release of toxic Gd3+ ions by vitamin B12 bioconjugates.
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86. 86
  Campello, M. P. C.; Lacerda, S.; Santos, I. C.; Pereira, G. A.; Geraldes, C. F. G. C.; Kotek, J.; Hermann, P.; Vaněk, J.; Lubal, P.; Kubíček, V.; Tóth, É.; Santos, I. Lanthanide(III) Complexes of 4,10-Bis(Phosphonomethyl)-1,4,7,10-Tetraazacyclododecane-1,7-Diacetic Acid (Trans-H6do2a2p) in Solution and in the Solid State: Structural Studies Along the Series. Chem. – Eur. J. 2010, 16 (28), 8446– 8465, DOI: 10.1002/chem.201000320
  86
  Lanthanide(III) Complexes of 4,10-Bis(phosphonomethyl)-1,4,7,10-tetraazacyclododecane-1,7-diacetic acid (trans-H6do2a2p) in Solution and in the Solid State: Structural Studies Along the Series
  Campello, M. Paula C.; Lacerda, Sara; Santos, Isabel C.; Pereira, Giovannia A.; Geraldes, Carlos F. G. C.; Kotek, Jan; Hermann, Petr; Vanek, Jakub; Lubal, Premysl; Kubicek, Vojtech; Toth, Eva; Santos, Isabel
  Chemistry - A European Journal (2010), 16 (28), 8446-8465, S8446/1-S8446/33CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)
  Complexes of 4,10-bis(phosphonomethyl)-1,4,7,10-tetraazacyclododecane-1,7-diacetic acid (trans-H6do2a2p, H6L) with transition metal and lanthanide(III) ions were studied. The stability const. values of the divalent and trivalent metal-ion complexes are between the corresponding values of H4dota and H8dotp complexes, as a consequence of the ligand basicity. The solid-state structures of the ligand and of nine lanthanide(III) complexes were detd. by x-ray diffraction. All the complexes are present as twisted-square-antiprismatic isomers and their structures can be divided into two series. The first one involves nonacoordinated complexes of the large lanthanide(III) ions (Ce, Nd, Sm) with a coordinated H2O mol. For Sm, Eu, Tb, Dy, Er, Yb, the complexes are octacoordinated only by the ligand donor atoms and their coordination cages are more irregular. The formation kinetics and the acid-assisted dissocn. of several LnIII-H6L complexes were studied at different temps. and compared with analogous data for complexes of other dota-like ligands. The [Ce(L)(H2O)]3- complex is the most kinetically inert among complexes of the studied lanthanide(III) ions (Ce, Eu, Gd, Yb). Among mixed phosphonate-acetate dota analogs, kinetic inertness of the Ce(III) complexes is increased with a higher no. of phosphonate arms in the ligand, whereas the opposite is true for Eu(III) complexes. According to the 1H NMR spectroscopic pseudo-contact shifts for the Ce-Eu and Tb-Yb series, the soln. structures of the complexes reflect the structures of the [Ce(HL)(H2O)]2- and [Yb(HL)]2- anions, resp., found in the solid state. However, these soln. NMR spectroscopic studies showed that there is no unambiguous relation between 31P/1H lanthanide-induced shift (LIS) values and coordination of H2O in the complexes; the values rather express a relative position of the central ions between the N4 and O4 planes.
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87. 87
  Vojtíšek, P.; Cígler, P.; Kotek, J.; Rudovský, J.; Hermann, P.; Lukeš, I. Crystal Structures of Lanthanide(III) Complexes with Cyclen Derivative Bearing Three Acetate and One Methylphosphonate Pendants. Inorg. Chem. 2005, 44 (16), 5591– 5599, DOI: 10.1021/ic048190s
  87
  Crystal Structures of Lanthanide(III) Complexes with Cyclen Derivative Bearing Three Acetate and One Methylphosphonate Pendants
  Vojtisek, Pavel; Cigler, Petr; Kotek, Jan; Rudovsky, Jakub; Hermann, Petr; Lukes, Ivan
  Inorganic Chemistry (2005), 44 (16), 5591-5599CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
  Lanthanide(III) complexes formulated as M[Ln(Hdo3ap)]·xH2O (M = Li; Ln = Tb, Dy, Lu, Y and M = H; Ln = Er, Lu) with the monophosphonate analog of H4dota, 1,4,7,10-tetraazacyclododecane-1,4,7-triacetic-10-methylphosphonic acid (I; H5do3ap), were prepd. and studied using x-ray crystallog. All of the structures show that the (Hdo3ap)4- anion is octadentate coordinated to a lanthanide(III) ion similarly to the other H4dota-like ligands, i.e., forming O4 and N4 planes that are parallel and have mutual angle smaller than 3°. The lanthanide(III) ions lie between these planes, closer to the O4 base than to the N4 plane. All of the structures present the lanthanide(III) complexes in their twisted-square-antiprismatic (TSA) configuration. Twist angles of the pendants vary in the range between -24 and -30°, and for each complex, they lie in a very narrow region of 1°. The coordinated phosphonate oxygen is located slightly above (0.02-0.19 Å) the O3 plane formed with the coordinated acetates. The Dy, Y and Lu complexes are isostructural and can be formulated as [{Li(H2O)3}{M(Hdo3ap)}]·2H2O. These three complexes have a tetrahedral lithium coordinated only to one acetate O and 3 water mols. A water mol. is coordinated only in the terbium(III) and neodymium(III) complexes. The bond distance Tb-Ow is unusually long (2.678 Å). The O-Ln-O angles decrease from 140° [Nd(III)] to 121° [Lu(III)], thus confirming the increasing steric crowding around the water binding site. A comparison of a no. of structures of Ln(III) complexes with DOTA-like ligands shows that the TSA arrangement is flexible. However, the SA arrangement is rigid, and the derived structural parameters are almost identical for different ligands and lanthanide(III) ions.
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88. 88
  Bondi, A. Van Der Waals Volumes and Radii. J. Phys. Chem. 1964, 68 (3), 441– 451, DOI: 10.1021/j100785a001
  88
  van der Waals volumes and radii
  Bondi, A.
  Journal of Physical Chemistry (1964), 68 (3), 441-51CODEN: JPCHAX; ISSN:0022-3654.
  Intermol. van der Waals radii of the nonmetallic elements were assembled into a list of recommended values for vol. calcns. These values were arrived at by selecting from the most reliable x-ray diffraction data those which could be reconciled with crystal d. at 0°K. (to give reasonable packing d.), gas kinetic collision cross section, crit. d., and with liquid state properties. A qual. understanding of the nature of van der Waals radii is provided by correlation with the de Broglie wavelength of the outermost valence electron. Tentative values for the van der Waals radii of metallic elements in organometallic compds. are proposed. A list of increments for the vol. of mols. impenetrable to thermal collision, the so-called van der Waals vol., and of the corresponding increments in area per mol. is given.
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89. 89
  Rowland, R. S.; Taylor, R. Intermolecular Nonbonded Contact Distances in Organic Crystal Structures: Comparison with Distances Expected from van Der Waals Radii. J. Phys. Chem. 1996, 100 (18), 7384– 7391, DOI: 10.1021/jp953141+
  89
  Intermolecular Nonbonded Contact Distances in Organic Crystal Structures: Comparison with Distances Expected from van der Waals Radii
  Rowland, R. Scott; Taylor, Robin
  Journal of Physical Chemistry (1996), 100 (18), 7384-91CODEN: JPCHAX; ISSN:0022-3654. (American Chemical Society)
  The conclusions derived from systematic analyses of intermol. contact distances in org. crystals may be affected by the values assumed for van der Waals radii. The most widely used tabulations of van der Waals radii date back 30 yr or more. Also, many of the tabulated values were chosen to reproduce vols., not contact distances, in crystals. Literally millions of nonbonded contact distances were characterized by crystallog. since the tabulations were compiled. A study has therefore been performed to establish the degree of consistency between these accumulated crystallog. data and the van der Waals radii of the common nonmetallic elements, as compiled by Pauling and Bondi. For halogens and S, the results show a remarkable agreement between obsd. contact distances and the Bondi radii. Agreement is slightly less good for C, N, and O, but discrepancies are still only ∼0.05 Å. However, there is a significant difference for H, where the Bondi value of 1.2 Å is probably too high by ∼0.1 Å.
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90. 90
  Fernández-Fernández, M. D. C.; Bastida, R.; Macías, A.; Pérez-Lourido, P.; Platas-Iglesias, C.; Valencia, L. Lanthanide(III) Complexes with a Tetrapyridine Pendant-Armed Macrocyclic Ligand: 1H NMR Structural Determination in Solution, X-Ray Diffraction, and Density-Functional Theory Calculations. Inorg. Chem. 2006, 45 (11), 4484– 4496, DOI: 10.1021/ic0603508
  90
  Lanthanide(III) Complexes with a Tetrapyridine Pendant-Armed Macrocyclic Ligand: 1H NMR Structural Determination in Solution, X-ray Diffraction, and Density-Functional Theory Calculations
  Fernandez-Fernandez, M. del C.; Bastida, R.; Macias, A.; Perez-Lourido, P.; Platas-Iglesias, C.; Valencia, L.
  Inorganic Chemistry (2006), 45 (11), 4484-4496CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
  Complexes between the tetrapyridyl pendant-armed macrocyclic ligand (L) and the trivalent lanthanide ions were synthesized, and structural studies were made both in the solid state and in aq. soln. The crystal structures of the La, Ce, Pr, Gd, Tb, Er, and Tm complexes were detd. by single-crystal x-ray crystallog. In the solid state, all the cation complexes show a 10-coordinated geometry close to a distorted bicapped antiprism, with the pyridine pendants situated alternatively above and below the main plane of the macrocycle. The conformations of the two five-membered chelate rings present in the complexes change along the lanthanide series. The La(III) and Ce(III) complexes show a λδ (or δλ) conformation, while the complexes of the heavier lanthanide ions present λλ (or δδ) conformation. The cationic [Ln(L)]3+ complexes (Ln = La, Pr, Eu, Tb, and Tm) were also characterized by theor. calcns. at the d.-functional theory (DFT) B3LYP level. The theor. calcns. predict a stabilization of the λλ (or δδ) conformation on decreasing the ionic radius of the Ln(III) ion, in agreement with the exptl. evidence. The soln. structures show a good agreement with the calcd. ones, as demonstrated by paramagnetic NMR measurements (lanthanide induced shifts and relaxation rate enhancements). The 1H NMR spectra indicate an effective D2 symmetry of the complexes in D2O soln. The 1H lanthanide induced shifts (LIS) obsd. for the Ce(III), Tm(III), and Yb(III) complexes can be fit to a theor. model assuming that dipolar contributions are dominant for all protons. The resulting calcd. values are consistent with highly rhombic magnetic susceptibility tensors with the magnetic axes being coincident with the symmetry axes of the mol. In contrast with the solid-state structure, the anal. of the LIS data indicates that the Ce(III) complexes present a λλ (or δδ) conformation in soln.
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91. 91
  Castro, G.; Regueiro-Figueroa, M.; Esteban-Gómez, D.; Bastida, R.; Macías, A.; Pérez-Lourido, P.; Platas-Iglesias, C.; Valencia, L. Exceptionally Inert Lanthanide(III) PARACEST MRI Contrast Agents Based on an 18-Membered Macrocyclic Platform. Chem. – Eur. J. 2015, 21 (51), 18662– 18670, DOI: 10.1002/chem.201502937
  91
  Exceptionally Inert Lanthanide(III) PARACEST MRI Contrast Agents Based on an 18-Membered Macrocyclic Platform
  Castro, Goretti; Regueiro-Figueroa, Martin; Esteban-Gomez, David; Bastida, Rufina; Macias, Alejandro; Perez-Lourido, Paulo; Platas-Iglesias, Carlos; Valencia, Laura
  Chemistry - A European Journal (2015), 21 (51), 18662-18670CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)
  We report a macrocyclic ligand based on a 3,6,10,13-tetraaza-1,8(2,6)-dipyridinacyclotetradecaphane platform contg. four hydroxyethyl pendant arms (L1) that forms extraordinary inert complexes with Ln3+ ions. The [EuL1]3+ complex does not undergo dissocn. in 1 M HCl over a period of months at room temp. Furthermore, high concns. of phosphate and Zn2+ ions at room temp. do not provoke metal-complex dissocn. The X-ray crystal structures of six Ln3+ complexes reveal ten coordination of the ligand to the metal ions through the six nitrogen atoms of the macrocycle and the four oxygen atoms of the hydroxyethyl pendant arms. The anal. of the Yb3+- and Pr3+-induced paramagnetic 1H NMR shifts show that the solid-state structures are retained in aq. soln. The intensity of the 1H NMR signal of bulk water can be modulated by satn. of the signals of the hydroxy protons of Pr3+, Eu3+, and Yb3+ complexes following chem.-exchange satn. transfer (CEST). The ability of these complexes to provide large CEST effects at 25 and 37 °C and pH 7.4 was confirmed by using CEST magnetic resonance imaging expts.
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92. 92
  Xing, Y.; Jindal, A. K.; Regueiro-Figueroa, M.; Le Fur, M.; Kervarec, N.; Zhao, P.; Kovacs, Z.; Valencia, L.; Pérez-Lourido, P.; Tripier, R.; Esteban-Gómez, D.; Platas-Iglesias, C.; Sherry, A. D. The Relationship between NMR Chemical Shifts of Thermally Polarized and Hyperpolarized 89Y Complexes and Their Solution Structures. Chem. – Eur. J. 2016, 22 (46), 16657– 16667, DOI: 10.1002/chem.201602901
  92
  The Relationship between NMR Chemical Shifts of Thermally Polarized and Hyperpolarized 89Y Complexes and Their Solution Structures
  Xing, Yixun; Jindal, Ashish K.; Regueiro-Figueroa, Martin; Le Fur, Mariane; Kervarec, Nelly; Zhao, Piyu; Kovacs, Zoltan; Valencia, Laura; Perez-Lourido, Paulo; Tripier, Raphael; Esteban-Gomez, David; Platas-Iglesias, Carlos; Sherry, A. Dean
  Chemistry - A European Journal (2016), 22 (46), 16657-16667CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)
  Recently developed dynamic nuclear polarization (DNP) technol. offers the potential of increasing the NMR sensitivity of even rare nuclei for biol. imaging applications. Hyperpolarized 89Y is an ideal candidate because of its narrow NMR linewidth, favorable spin quantum no. (I=1/2), and long longitudinal relaxation times (T1). Strong NMR signals were detected in hyperpolarized 89Y samples of a variety of yttrium complexes. A dataset of 89Y NMR data composed of 23 complexes with polyaminocarboxylate ligands was obtained using hyperpolarized 89Y measurements or 1H,89Y-HMQC spectroscopy. These data were used to derive an empirical equation that describes the correlation between the 89Y chem. shift and the chem. structure of the complexes. This empirical correlation serves as a guide for the design of 89Y sensors. Relativistic (DKH2) DFT calcns. were found to predict the exptl. 89Y chem. shifts to a rather good accuracy.
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93. 93
  Gambino, T.; Valencia, L.; Pérez-Lourido, P.; Esteban-Gómez, D.; Zaiss, M.; Platas-Iglesias, C.; Angelovski, G. Inert Macrocyclic Eu ³⁺ Complex with Affirmative paraCEST Features. Inorg. Chem. Front. 2020, 7 (12), 2274– 2286, DOI: 10.1039/C9QI01612K
  93
  Inert macrocyclic Eu3+ complex with affirmative paraCEST features
  Gambino, Tanja; Valencia, Laura; Perez-Lourido, Paulo; Esteban-Gomez, David; Zaiss, Moritz; Platas-Iglesias, Carlos; Angelovski, Goran
  Inorganic Chemistry Frontiers (2020), 7 (12), 2274-2286CODEN: ICFNAW; ISSN:2052-1553. (Royal Society of Chemistry)
  We report on a macrocyclic platform based on an 18-membered macrocycle that forms kinetically highly inert paramagnetic complexes and possesses an excellent outlook for the development of bioresponsive paraCEST (paramagnetic chem. exchange satn. transfer) contrast agents. The investigated europium(III) chelate is non-hydrated and contains four amide groups, each possessing two paramagnetically shifted proton resonances distant from bulk water. The X-ray crystal structure and soln. studies indicate that the metal ion is ten-coordinated, being directly bound to the six N atoms of the macrocycle and the four amide O atoms of the pendant arms. The complex presents an excellent inertness with respect to dissocn., being stable under a variety of harsh conditions, including highly acidic and basic media or elevated temps. The amide protons are in slow-to-intermediate exchange with bulk water, which gives rise to the generation of a strong CEST effect at low probe concn. and satn. powers (~ 25% at 5 mM, B1 = 5 μT, 37 °C). We demonstrate the potential of this platform for mapping pH in its microenvironment and foresee potential for the development of diverse paraCEST probes and sensors.
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94. 94
  Harriswangler, C.; Caneda-Martínez, L.; Rousseaux, O.; Esteban-Gómez, D.; Fougère, O.; Pujales-Paradela, R.; Valencia, L.; Fernández, M. I.; Lepareur, N.; Platas-Iglesias, C. Versatile Macrocyclic Platform for the Complexation of [natY/90Y]Yttrium and Lanthanide Ions. Inorg. Chem. 2022, 61 (16), 6209– 6222, DOI: 10.1021/acs.inorgchem.2c00378
  94
  Versatile Macrocyclic Platform for the Complexation of [natY/90Y]Yttrium and Lanthanide Ions
  Harriswangler, Charlene; Caneda-Martinez, Laura; Rousseaux, Olivier; Esteban-Gomez, David; Fougere, Olivier; Pujales-Paradela, Rosa; Valencia, Laura; Fernandez, M. Isabel; Lepareur, Nicolas; Platas-Iglesias, Carlos
  Inorganic Chemistry (2022), 61 (16), 6209-6222CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
  We report a macrocyclic ligand (H3L6) based on a 3,6,10,13-tetraaza-1,8(2,6)-dipyridinacyclotetradecaphane platform contg. three acetate pendant arms and a benzyl group attached to the fourth nitrogen atom of the macrocycle. The X-ray structures of the YL6 and TbL6 complexes reveal nine coordination of the ligand to the metal ions through the six nitrogen atoms of the macrocycle and three oxygen atoms of the carboxylate pendants. A combination of NMR spectroscopic studies (1H, 13C, and 89Y) and DFT calcns. indicated that the structure of the YL6 complex in the solid state is maintained in an aq. soln. The detailed study of the emission spectra of the EuL6 and TbL6 complexes revealed Ln3+-centered emission with quantum yields of 7.0 and 60%, resp. Emission lifetime measurements indicate that the ligand offers good protection of the metal ions from surrounding water mols., preventing the coordination of water mols. The YL6 complex is remarkably inert with respect to complex dissocn., with a lifetime of 1.7 h in 1 M HCl. On the other hand, complex formation is fast (~ 1 min at pH 5.4, 2 × 10-5 M). Studies using the 90Y-nuclide confirmed fast radiolabeling since [90Y]YL6 is nearly quant. formed (radiochem. yield (RCY) > 95) in a short time over a broad range of pH values from ca. 2.4 to 9.0. Challenging expts. in the presence of excess EDTA and in human serum revealed good stability of the [90Y]YL6 complex. All of these expts. combined suggest the potential application of H3L6 derivs. as Y-based radiopharmaceuticals.
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- CCDC: 2266985
Supporting Information
Supporting Information
The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.inorgchem.3c03126.
- Computational details, crystallographic data (CCDC 2266985), additional plots showing calculated electron densities, linear fits according to eq 1, and bond distances used in this work with CSD codes (PDF)
- ic3c03126_si_001.pdf (2.22 MB)
Accession Codes
CCDC 2266985 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

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Donor Radii in Rare-Earth ComplexesClick to copy article linkArticle link copied!

Inorganic Chemistry

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Inorganic Chemistry

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Donor Radii in Rare-Earth Complexes
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