ACS Publications. Most Trusted. Most Cited. Most Read
Variation of Spin-Transition Temperature in the Iron(III) Complex Induced by Different Compositions of the Crystallization Solvent
More

OR SEARCH CITATIONS

My Activity
Publications

Figure 1Loading Img
Download Hi-Res ImageDownload to MS-PowerPointCite This:Crystal Growth & Design 2023, 23, 3, 1323-1329
  • Open Access
Communication

Variation of Spin-Transition Temperature in the Iron(III) Complex Induced by Different Compositions of the Crystallization Solvent
Click to copy article linkArticle link copied!

Open PDFSupporting Information (1)

Crystal Growth & Design

Cite this: Cryst. Growth Des. 2023, 23, 3, 1323–1329
Click to copy citationCitation copied!
https://doi.org/10.1021/acs.cgd.2c01411
Published February 16, 2023

Copyright © 2023 American Chemical Society. This publication is licensed under

CC-BY 4.0 .

Abstract

Click to copy section linkSection link copied!
High Resolution Image
Download MS PowerPoint Slide

We crystallized the Schiff-base iron(III) spin-crossover complex [Fe(3,5Cl-L5)(NCSe)] from different two-component solvent mixtures containing methanol and chloroform (Φ = V(CH3OH)/V(solvent) = 0.05, 0.25, 0.50, 0.83, and 1.00). The obtained crystalline products were characterized by X-ray diffraction, and it was confirmed that they are all composed of the same crystalline phase, and they do not contain any crystal solvent. However, significant differences in magnetic properties were observed, and thermal hysteresis changed from (in K) 121T↓ and 134T↑ for Φ = 0.05 and 0.25, down to 72T↓ and 96T↑ for Φ = 1.00. The crystal structures of the low-spin and high-spin phases were studied theoretically and experimentally.

This publication is licensed under

CC-BY 4.0 .
  • cc licence
  • by licence
Copyright © 2023 American Chemical Society

Subjects

what are subjects

Special Issue

Published as part of a Crystal Growth and Design virtual special issue on Molecular Magnets and Switchable Magnetic Materials

Synopsis

The iron(III) Schiff-base spin-crossover complex [Fe(3,5Cl-L5)(NCSe)] exhibits a large variation of spin transition temperature and hysteresis loop width stimulated by the composition of a two-component solvent mixture containing methanol and chloroform. The relationship between crystal quality and T1/2 has been extensively studied.

The tunability of the spin-crossover (SCO) behavior is an important assumption for versatile applications of SCO materials. Beneficially, SCO parameters such as thermal hysteresis width, transition temperature (T1/2), cooperativity degree, curve abruptness, and completeness can be manipulated by sample modifications. The effect of the presence (1−3) and loss (4) of a solvent molecule in the lattice, the selection of an anion, (5,6) as well as the choice of a side substituent (6−8) are well-known strategies for modifying the SCO behavior. Also, metal dilution represents a sophisticated approach for modification of the SCO behavior and observing of the cooperativity degree and transition temperature of SCO materials. The SCO behavior can be also tuned by a postsynthetic modification as was manifested by solid state performed anion metathesis. (9)

Our ongoing interest in the magnetic behavior of Fe(III) complexes with pentadentate Schiff base ligands has brought remarkable results on distinct magnetic behaviors of polymorphs within this class of compounds, (10) or hydrogen bonding induced modification of T1/2. (11) Recently, a new report on SCO with broad thermal hysteresis observed for an Fe(III) complex with a pentadentate Schiff base ligand H23,5Cl-L5 (N,N′-bis(1-hydroxy-3,5-dichloro-2-benzyliden)-1,6-diamino-4-azahexane) has been reported by Renz et al. which naturally caught our attention. (12) Complex [Fe(3,5-Cl-L5)(NCSe)] (1) exhibits thermally induced SCO with 24 K wide thermal hysteresis (T1/2 = 99↓ and 129↑ K). From the comparison of the low-spin (LS, S = 1/2) and high-spin (HS, S = 5/2) crystal structures, it is apparent that reorganization of noncovalent interactions (H···Cl and Cl···Cl) happens upon spin transition. This, if significant, could explain the observation of the wide thermal hysteresis. In the original report, (12) the authors did not investigate this possibility in greater detail, and therefore, our original motivation for studying this system was to extensively theoretically and experimentally investigate the LS and HS crystal structures of 1.

For the preparation of 1 we used a procedure similar to that in the original report, (12) but instead of an ultrasonic bath we used a standard magnetic stirrer. The reaction between [Fe(3,5-Cl-L5)Cl] and KNCSe in pure methanol led to precipitation of a brown microcrystalline powder, which was filtered off using a paper filter. For the preparation of the single-crystals suitable for X-ray diffraction experiments we used the remaining mother liquor which was crystallized isothermally. After several days thin needle-like crystals were obtained. First, we collected the diffraction data for the HS state (150 K), and then we attempted to measure the LS state crystal structure at 90 K as was done in the original report. (12) To our surprise, the measurement revealed the crystal structure with the very same metal–ligand bond lengths and unit cell parameters as was observed for the HS phase. Obviously, this did not match the previously reported magnetic properties. (12) Therefore, we measured the temperature dependence of the magnetic moment (μeff/μB) for two obtained fractions, needle-like crystals (1_Φ1) and microcrystalline powder precipitate (1_Φ1p). The measurements confirmed the presence of SCO with thermal hysteresis for both batches; however, the critical temperatures and profiles of magnetic functions were different (Figure 1). The 1_Φ1 batch exhibited much lower T1/2 (72↓ and 96↑ K, ΔT = 24 K) than 1_Φ1_p (106↓ and 129↑ K, ΔT = 23 K, Figure 1). Powder X-ray diffraction undoubtedly confirmed that both samples were the same crystallographic phase identical to the HS structure of 1 (Supporting Information, Figure S6–S7).

Figure 1

Figure 1. Temperature dependence of μeff/μB for 1_Φ1 and 1_Φ1p.

High Resolution Image
Download MS PowerPoint Slide

Inspired by this intriguing inconsistency, we investigated this phenomenon in greater detail. From magnetic measurements it is apparent that the low T1/2 was observed for the batch composed of crystals which grew more than 5 days, whereas the high T1/2 was observed for the precipitate. Therefore, one of the tested hypotheses was that different critical temperatures were related to the crystallinity of the samples, which is related to the time of the crystallization. In an attempt to prepare crystals, whose crystallization spans different time periods, we modified the composition of crystallization solutions from pure CH3OH to solutions with a growing portion of CHCl3. CHCl3 was chosen as the second solvent because it dissolves 1 very well; it does not enter the crystal structure of 1 (does not form a solvate) and has a similar boiling temperature as CH3OH. Therefore, it could be expected that the crystallization of 1 will be governed by slow evaporation of the solvent mixture. This mixture gradually loses slightly more CHCl3 than CH3OH molecules (because of higher vapor pressure of CHCl3), and thus the solubility of 1 should be continuously decreasing. Four different crystallization mixtures with a different volume fraction Φ of CH3OH were prepared (Φ = 0.83, 0.50, 0.25 and 0.05), and the corresponding crystalline samples (1_Φ0.83, 1_Φ0.50, 1_Φ0.25, 1_Φ0.05) were obtained. In the case of the solutions with Φ > 0.5 also microcrystalline precipitates 1_Φ0.83p (besides already prepared 1_Φ1_p) were obtained and were included into this study. The purity of all the prepared samples was confirmed by X-ray powder diffraction. It must be noted that in the case of one of the precipitates (1_Φ1_p), the presence of KCl impurity was detected as this is a side product of the ligand metathesis (Cl– ligand was substituted by KNCSe). We decided not to wash the precipitates with water (which would dissolve the impurity), because it would introduce a third solvent into the studied system. Furthermore, the presence of the diamagnetic KCl should not affect the SCO temperatures.

1 crystallizes as very thin needle-shaped crystals. The symmetry of the crystals is monoclinic with the P21/n space group (see Supporting Information, Table S1). The crystal structures of LS and HS phases were well described in the original report, (12) and we will not add a new structural description here.

The best quality crystals were obtained for the batch 1_Φ0.25. Again, we opted to measure the LS and HS crystal structures using a selected single crystal from this batch. We monitored SCO using diffraction methods. Therefore, we started the single crystal X-ray diffraction experiments at 140 K, and we collected sets of diffraction data at selected temperatures on cooling and also on heating. At 116 K (on cooling), a dramatic change in the quality of diffractions occurred as this was the T1/2↓ temperature. The crystal structure of 1_Φ0.25@↓116K shows metal–ligand (ML) bond lengths significantly shorter (Table S2) than observed at higher temperatures and in very good agreement with the LS structure of 1 reported in the original paper. (12) Upon further cooling (down to 108 K), neither the M–L bond lengths nor the unit cell parameters changed significantly, and therefore, we can conclude that the full HS → LS spin conversion occurred between 116 and 117 K (Figure 2). Upon heating, we detected the LS → HS transition between 133 (LS) and 135 K (HS structure), whereas we were not able to get reasonable data from the measurement at 134 K. We attempted to also measure another SCO thermal cycle, but the crystal cracked upon another cooling. Here, we may conclude that the single crystal X-ray diffraction measurements confirmed that 1_Φ0.25 exhibits thermally induced SCO with hysteresis wide 18 K (if we assume T1/2↑ to be 134 K). This is not in agreement with the magnetic data reported in the original paper, (12) but it is also not in good agreement with the magnetic data measured for 1_Φ1p. Of note here is that the coordinates of the non-hydrogen atoms in the HS crystal structure of 1_Φ1 (at 90 K) are almost identical with those determined for 1_Φ0.25 (at 130 K, see Supporting Information, Figure S1) and thus, the difference in T1/2 cannot be assigned to changes in the crystal structures.

Figure 2

Figure 2. Temperature dependence of μeff/μB for 1_Φ0.25 (top) and the temperature dependence of the selected unit cell parameters as determined from the single crystal X-ray diffraction experiment for 1_Φ0.25 (bottom).

High Resolution Image
Download MS PowerPoint Slide

We performed magnetic measurements for all the prepared batches. The results showed that all the samples show thermally induced spin crossover (Figure S2 and Figure S3). Remarkably, it is obvious that the batches prepared from the mixture with the largest content of methanol showed hysteretic loops shifted to lower temperatures, whereas the batches from the higher CHCl3 content had hysteretic loops shifted to higher temperatures (Figure S2). The shift of hysteretic loops is observable also between 1_Φ0.83 and 1_Φ1; however, the data for their precipitates 1_Φ0.83p and 1_Φ1p did not show a significant difference in T1/2 (Figure S3). The hysteretic loops for the batches with the highest CHCl3 content (1_Φ0.25 and 1_Φ0.05) are very similar, and they exhibit the highest T1/2. The magnetic behavior of 1_Φ0.25 fits the temperature dependence of the unit cell parameters rather well (Figure 2). The observed behavior is reproducible.

The magnetic data were analyzed by using an Ising-like model (ISM) with Gaussian distribution of the cooperativity parameter derived by Boča et al. (13) Within the ISM defined by the Hamiltonian

H^=Δ2σ^−Γ⟨σ⟩σ^
(1)
the transition between two spin states, σ = −1 for LS and σ = +1 for HS states, is governed by the energy difference between HS and LS states (Δ) and the cooperativeness of the system (Γ). Such a model can be modified to also include the distribution of the cooperativity parameter Γ in order to deal with the imperfections of the crystalline/powder samples by varying the standard deviation parameter σ of the Gaussian distribution function. The main advantage of such a model is its ability to reproduce the slope of the hysteresis loops, and hence better agreement with the experimental data can be achieved. Thus, the magnetic data were fitted by varying Δ, Γ, reff, and σ parameters within ISM, and subsequently calculated x′HS for given temperature was used to calculate total molar susceptibility as
x″HS=x′HS(1−xrHS)
(2)
χmol=(x″HS+xrHS)χHS+(1−x″HS−xrHS)χHS
(3)
where xrHS is the residual molar fraction of the HS state at a low temperature due to incomplete spin crossover, and x″HS is rescaled high-spin fraction calculated from ISM resulting in the total high-spin mole fraction xHS equal to xHS = x″HS + xrHS. The molar susceptibility of the HS and LS species was calculated by the Curie law. The fitted parameters are listed in Table S3 and plotted in Figure 3 for crystal samples and in Figure S4 for microcrystalline precipitates. Evidently, there is small variation of the cooperativity Γ and entropy parameter reff within the prepared crystal batches of 1, and variations of T1/2↓ and T1/2↑ are mainly due to a variation of Δ. Furthermore, there is a significant increase of the distribution parameter σ for the microcrystalline precipitates, Table S3.

Figure 3

Figure 3. Temperature dependence the high-spin molar fraction xHS according to ISM (top), the ISM parameters (middle), and transition temperatures (bottom) for crystalline samples of 1.

High Resolution Image
Download MS PowerPoint Slide

We also theoretically attempted to investigate the impact of different solvents on the molecular geometry and the energies of the LS and HS isomer of 1 using density functional theory (DFT) and utilizing ORCA 5.0 software. (14) We selected three functionals based on published benchmark studies, (15−17) namely, OPBE, (18) r2SCAN, (19) and B3LYP* (B3LYP with reduced Hartree–Fock exchange to 15%) (20) and also included the atom-pairwise dispersion correction (D4). (21) The optimization was done in a vacuum, chloroform, and methanol with the C-PCM implicit solvation model. (22,23) Impact of solvents is demonstrated for the HS state of [Fe(3,5-Cl-L5)(NCSe)] in Figure 4. It seems that OPBE underestimates the Fe–NCSe bond, whereas B3LYP* and r2SCAN overestimates the bond lengths to amino-nitrogen of 3,5-Cl-L5. In the case of the LS molecular geometries, OPBE heavily underestimates all Fe–N bond lengths (Figure S5). Moreover, there is also significant variation in bond lengths induced by the implicit solvation model, which points to the importance of intermolecular interactions.

Figure 4

Figure 4. Graphical comparison of the donor–acceptor bond distances between X-ray data (dotted lines) and the respective DFT methods (B3LYP*, OPBE, and r2SCAN) for the high-spin state of 1.

High Resolution Image
Download MS PowerPoint Slide

The analysis of the electronic energy differences between the HS and LS isomers revealed positive values of ΔEel = EelHS – EelLS for all three DFT functionals, and thus these functionals properly found the LS state with lower electronic energy (Eel), Table S4. As the molecular vibrations have a significant impact on the SCO properties, a better description is achieved with the energy difference corrected by the zero-temperature vibrational energy from the frequency calculation, ΔEel+ZPE, which is depicted in Figure 5.

Figure 5

Figure 5. Graphical comparison the energy difference corrected by the zero-temperature vibrational energy from the frequency calculation ΔEel+ZPE between the HS and LS states for different DFT methods applied to 1.

High Resolution Image
Download MS PowerPoint Slide

Apparently, ΔEel+ZPE is significantly affected by applying the implicit solvation model, and both B3LYP*and r2SCAN provided reasonable values of the HS-LS separation. Moreover, it seems that a more polar solvent like CH3OH tends to increase ΔEel+ZPE, and thus it stabilizes the LS state. This is in contradiction to the experimental finding (Figure 3 and Table S3), for which higher Φ(CH3OH) yielded lower Δ and T1/2 values. We can speculate that this discrepancy is caused by the implicit solvation approach which cannot grasp the effect of all intermolecular interactions properly, or the properties of 1 in the solid state simply cannot be encompassed by such an approach at all.

However, if the presented theoretical calculations are not deceptive, perhaps it most likely leads to the conclusion that the reported phenomenon is not governed by thermodynamics, but by the kinetics of the crystal growth of 1 under various contents of chloroform and methanol in crystallizing solutions. Hence, the quality of the crystalline material and SCO properties are affected by a solvent mixture, but the solvent molecules do not cocrystallize. One of the possible approaches to test this hypothesis is to correlate parameters such as crystal mosaicity with the observed magnetic behavior. Therefore, we decided to prepare several batches of 1 crystallized at different crystallization rates. As was mentioned above, the best crystals were obtained in the batch of 1_Φ0.25. However, the batches crystallized from solutions with a major chloroform fraction (Φ0.25 and Φ0.05) have practically the same magnetic properties (Figure 3). Thus, we decided to crystallize 1 from Φ0.5 and Φ0.83 solutions, because 1_Φ0.5 and 1_Φ0.83 differ in T1/2↓ (114 K for 1_Φ0.5 and 103 K for 1_Φ0.83), and their spin transition on cooling is still accessible using standard commercial cryogenic devices (above 80 K). For preparation of the batches, we used the same reaction procedures as are described in Supporting Information, but the mother liquors were crystallized using three different crystallization rates: fast (≈1day), slow (up to 4 days), and very slow (≥7 days). The majority of the used single crystals were obtained for all the batches crystallized from Φ0.5 solutions regardless of the rate of crystallization used. However, also very slow crystallization from the Φ0.83 solutions resulted in the production of a few suitable single crystals.

The crystal mosaicity was determined taking into consideration the results of previous work on mosaicity in SCO complexes. (24) We set experimental conditions to be as identical as possible for all the investigated specimens. The experiment was conducted at 150 K, which is well above the highest T1/2↓ (Table S3). The data were collected using ω-scans (width 0.5 deg), and the exposition time was adjusted for each crystal based on its size, aiming for 0.83 Å resolution, completeness above 99%, data redundancy > 3, and I/σ > 10. As was already mentioned, the crystals of 1 are very thin (typically ≈0.05 mm in two dimensions), needle-like shaped growing in clumps of overlapping specimens, which makes it challenging to investigate the statistically relevant number of crystallites within a reasonable measurement time. Thus, we were capable of performing measurements for a limited number (14) of single crystals. It is important to note that the vast majority of the prepared crystals were not suitable for single-crystal experiments, and thus the results obtained only represent those crystals that met the necessary criteria.

After collecting each set of data at 150 K, we determined T1/2↓ for each crystal by measuring unit cell parameters starting from 125 K down to 80 K in decrements of 5 K. The occurrence of the SCO phenomenon was recorded between two measured temperature points, and the average of these values was used for visualization purposes. The T1/2↓ value of crystals that remained in the high spin phase at 80 K was set to 70 K for visualization purposes. The distribution of the determined T1/2↓ values is shown (Figure 6A). The results supported our hypothesis that the speed of crystallization affects the quality of crystals and the T1/2↓ value. Crystals crystallized in the ”fast” and “slow” modes showed T1/2↓ values above 100 K. Crystals that crystallized “very slowly” showed T1/2↓ values below 90 K with most of them having T1/2↓ even below 80 K.

Figure 6

Figure 6. Plot of T1/2↓ versus crystallization rate (A). The colored boxes are used to highlight the crystallization rate, with a lighter color indicating slower crystallization. The plots of Rint vs T1/2↓ (B), e3 vs T1/2↓ (C), and eavg vs T1/2↓ (D). The value of eavg was calculated as the arithmetic average of components e1, e2, and e3. In all plots, the T1/2↓ value of crystals that remained in the high spin phase down to 80 K was assigned as 70 K for visualization purposes.

High Resolution Image
Download MS PowerPoint Slide

The results of the X-ray diffraction measurements were evaluated in the CrysAlisPro software. (25) As a first indication of the crystal quality, we inspected the equivalency of symmetry equivalent reflections (Rint) in the studied crystals. There is no strong correlation between T1/2↓ and Rint, but apparently, the crystals with lower T1/2↓ values tend to have larger Rint and vice versa (Figure 6B).

The CrysAlisPro software provides the mosaicity in three directions (e1, e2, and e3) by fitting a Gaussian function to the peak. (26,27) Although these parameters do not measure the mosaicity directly, variations in the values of e1, e2, and e3 can indicate changes in the mosaicity of the studied crystals and thus their quality. (28) Some authors only use the e3 parameter due to its correlation with mosaicity values obtained from other data integration methods. (26) The results revealed that the e2 component varied slightly among the measurements (0.76–0.96°), while larger variations were observed for e1 (0.75–2.61°) and e3 (0.71–1.66°). As per previous reports, for evaluation of mosaicity, we considered the values of e3 and the arithmetic average (eavg) (29) of all three components e1, e2, and e3 (Figure 6C–D, Table S5). As with Rint, the results for eavg and e3 did not show a strong linear correlation; however, crystals with higher T1/2↓ values tend to have lower values of e and e3 and vice versa.

In summary, to the best of our knowledge, such an unprecedented solvent-induced variation of SCO spin-transition temperature as was discussed for 1 has not been reported yet. We showed that the different crystallization rates produced crystals exhibiting different SCO critical temperatures. Very slow crystallization (≥7 days) of the Φ0.5 and Φ0.83 solutions resulted into crystals exhibiting low SCO critical temperatures (T1/2↓ < 90 K), while faster crystallization (shorter than 4 days) led to larger T1/2↓ values (>100 K). The performed diffraction experiments indicate that crystals with low T1/2↓ values tend to have larger mosaicity parameters and Rint, and thus they are of lower quality than those with larger T1/2↓ values.

Supporting Information

Click to copy section linkSection link copied!

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.cgd.2c01411.

  • Synthesis, crystallographic data, magnetic measurements, DFT calculation details, and powder diffraction patterns (PDF)

Accession Codes

CCDC 1909057 and 2223462–2223463 contain 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.

Terms & Conditions

Most electronic Supporting Information files are available without a subscription to ACS Web Editions. Such files may be downloaded by article for research use (if there is a public use license linked to the relevant article, that license may permit other uses). Permission may be obtained from ACS for other uses through requests via the RightsLink permission system: http://pubs.acs.org/page/copyright/permissions.html.

Author Information

Click to copy section linkSection link copied!
  • Corresponding Authors
  • Author
  • 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

Click to copy section linkSection link copied!

The authors (I.N. and R.H.) acknowledge financial support from institutional sources of the Department of Inorganic Chemistry and Palacký University Olomouc, Czech Republic. We also acknowledge the CzechNanoLab Research Infrastructure supported by MEYS CR (LM2018110) for the measurement of some of the magnetic data. I.N. is grateful to Jakub Wojciechowski for discussions about mosaicity evaluation in CrysAlisPro software.

References

Click to copy section linkSection link copied!

This article references 29 other publications.

  1. 1
    Bari, R. A.; Sivardière, J. Low-Spin-High-Spin Transitions in Transition-Metal-Ion Compounds. Phys. Rev. B 1972, 5 (11), 4466– 4471,  DOI: 10.1103/PhysRevB.5.4466
    Google Scholar
    There is no corresponding record for this reference.
  2. 2
    Wajnflasz, J. Etude de La Transition “Low Spin”-“High Spin” Dans Les Complexes Octaédriques d’ion de Transition. Phys. status solidi 1970, 40 (2), 537– 545,  DOI: 10.1002/pssb.19700400212
    Google Scholar
    2
    "Low-spin"-"high-spin" transition in transition ion octahedral complexes
    Wajnflasz, J.
    Physica Status Solidi (1970), 40 (2), 537-45CODEN: PHSSAK; ISSN:0031-8957.
    Some 6-coordinated transition-ion complexes show an abnormal variation of the no. of Bohr magnetons with temp. These complexes have 2 stable equil. states simultaneously characterized by 2 different ionic radii and by fundamental states of a few hundred degrees Kelvin apart, which belong to 2 different representations. The cryst. fields assocd. with these 2 equil. states are on both sides of Δπ, the mean pairing energy. An Ising model with an interaction between neighboring transition ions can explain the magnetic behavior of these complexes and delimit an area of existence of a first-order transition between "low-spin" and "high-spin" states.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaE3cXkvFWnt7Y%253D&md5=bba310f775ebac7608c32590fe630cfe
  3. 3
    Boča, R.; Linert, W. Is There a Need for New Models of the Spin Crossover? In Molecular Magnets Recent Highlights; Springer Vienna: Vienna, 2002; pp 83– 100 DOI: 10.1007/978-3-7091-6018-3_6 .
    Google Scholar
    There is no corresponding record for this reference.
  4. 4
    Shakirova, O. G.; Lavrenova, L. G.; Kurat’eva, N. V.; Naumov, D. Y.; Daletskii, V. A.; Sheludyakova, L. A.; Logvinenko, V. A.; Vasilevskii, S. F. Spin Crossover in Iron(II) Complexes with Tris(Pyrazol-1-Yl)Methane. Russ. J. Coord. Chem. 2010, 36 (4), 275– 283,  DOI: 10.1134/S1070328410040068
    Google Scholar
    4
    Spin crossover in iron(II) complexes with tris(pyrazol-1-yl)methane
    Shakirova, O. G.; Lavrenova, L. G.; Kurat'eva, N. V.; Naumov, D. Yu.; Daletskii, V. A.; Sheludyakova, L. A.; Logvinenko, V. A.; Vasilevskii, S. F.
    Russian Journal of Coordination Chemistry (2010), 36 (4), 275-283CODEN: RJCCEY; ISSN:1070-3284. (Pleiades Publishing, Ltd.)
    Mononuclear iron(II) coordination compds. with tris(pyrazol-1-yl)methane (HC(Pz)3) described as [Fe{HC(Pz)3}2]A2.nH2O, [A = Cl-, Br-, I-, 1/2 SO2-4, n = 0-7] were synthesized. The compds. were studied by static magnetic susceptibility measurements, IR and UV/Vis spectroscopy, and powder X-ray diffraction. The crystal and mol. structures of all compds. were detd. by single crystal X-ray diffraction.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXlsVyjsLk%253D&md5=464456bfb6fafd609256baa551a83717
  5. 5
    Halcrow, M. A. Structure:Function Relationships in Molecular Spin-Crossover Complexes. Chem. Soc. Rev. 2011, 40 (7), 4119,  DOI: 10.1039/c1cs15046d
    Google Scholar
    5
    Structure:function relationships in molecular spin-crossover complexes
    Halcrow, Malcolm A.
    Chemical Society Reviews (2011), 40 (7), 4119-4142CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
    A review. Spin-crossover compds. are becoming increasingly popular for device and sensor applications, and in soft materials, that make use of their switchable color, paramagnetism and cond. The de novo design of new solid spin-crossover compds. with pre-defined switching properties is desirable for application purposes. This challenging problem of crystal engineering requires an understanding of how the temp. and cooperativity of a spin-transition are influenced by the structure of the bulk material. Towards that end, this crit. review presents a survey of mol. spin-crossover compds. with good availability of crystallog. data. A picture is emerging that changes in mol. shape between the high- and low-spin states, and the ability of a lattice to accommodate such changes, can play an important role in detg. the existence and the cooperativity of a thermal spin-transition in the solid state (198 refs.).
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXns12msrc%253D&md5=2a525c09d4f8ac62d2d305af3b4d8f36
  6. 6
    Roubeau, O. Triazole-Based One-Dimensional Spin-Crossover Coordination Polymers. Chem. - A Eur. J. 2012, 18 (48), 15230– 15244,  DOI: 10.1002/chem.201201647
    Google Scholar
    6
    Triazole-Based One-Dimensional Spin-Crossover Coordination Polymers
    Roubeau, Olivier
    Chemistry - A European Journal (2012), 18 (48), 15230-15244CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)
    A review. One-dimensional coordination FeII polymers constructed through triple N1,N2-1,2,4-triazole bridges form a unique class of spin-crossover materials, the synthetic versatility of which allows tuning the spin-crossover properties, the design of gels, films, liq. crystals, and nanoparticles and single-particle addressing. This Minireview provides the 1st complete overview of these very attractive switchable materials and their most recent developments.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38Xhs1agtbbN&md5=3e4be5c36be98a60071085372aff6a43
  7. 7
    Arcis-Castíllo, Z.; Zheng, S.; Siegler, M. A.; Roubeau, O.; Bedoui, S.; Bonnet, S. Tuning the Transition Temperature and Cooperativity of Bapbpy-Based Mononuclear Spin-Crossover Compounds: Interplay between Molecular and Crystal Engineering. Chem. - A Eur. J. 2011, 17 (52), 14826– 14836,  DOI: 10.1002/chem.201101301
    Google Scholar
    7
    Tuning the Transition Temperature and Cooperativity of bapbpy-Based Mononuclear Spin-Crossover Compounds: Interplay between Molecular and Crystal Engineering
    Arcis-Castillo, Zulema; Zheng, Sipeng; Siegler, Maxime A.; Roubeau, Olivier; Bedoui, Salma; Bonnet, Sylvestre
    Chemistry - A European Journal (2011), 17 (52), 14826-14836CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)
    (1) Different isomers of the same mononuclear iron(II) complex give materials with different spin-crossover (hereafter SCO) properties, and (2) minor modifications of the bapbpy (bapbpy = N6,N6'-di(pyridin-2-yl)-2,2'-bipyridine-6,6'-diamine) ligand allows SCO to be obtained near room temp. The authors also provide a qual. model to understand the link between the structure of bapbpy-based ligands and the SCO properties of their iron(II) compds. Thus, seven new trans-[Fe{R2(bapbpy)}(NCS)2] compds. were prepd., in which the R2bapbpy ligand bears picoline (9-12), quin-2-oline (13), isoquin-3-oline (14), or isoquin-1-oline (15) substituents. From this series, three compds. (12, 14, and 15) have SCO properties, one of which (15) occurs at 288 K. The crystal structures of 11, 12, and 15 show that the intermol. interactions in these materials are similar to those found in the parent compd. [Fe(bapbpy)(NCS)2] (1), in which each iron complex interacts with its neighbors through weak N-H···S hydrogen bonding and π-π stacking. For 12 and 15, hindering groups located near the N-H bridges weaken the N-S intermol. interactions, which is correlated to non-cooperative SCO. For 14, the substitution is further away from the N-H bridges, and the SCO remains cooperative as in 1 with a hysteresis cycle. Optical microscopy photographs show the strikingly different spatio-temporal evolution of the phase transition in the noncooperative SCO compd. 12 relative to that found in 1. Heat-capacity measurements were made for 1, 12, 14, and 15 and fitted to the Sorai domain model. The no. n of like-spin SCO centers per interacting domain, which is related to the cooperativity of the spin transition, was found high for 1 and 14 and low for 12 and 15. Finally, although both pairs of 11/12 and 14/15 are pairs of isomers their SCO properties are surprisingly different.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXhsFGrsr%252FM&md5=b6ccb49019aa18666ad0e556ba7d85ac
  8. 8
    Feltham, H. L. C.; Johnson, C.; Elliott, A. B. S.; Gordon, K. C.; Albrecht, M.; Brooker, S. “Tail” Tuning of Iron(II) Spin Crossover Temperature by 100 K. Inorg. Chem. 2015, 54 (6), 2902– 2909,  DOI: 10.1021/ic503040f
    Google Scholar
    8
    "Tail" Tuning of Iron(II) Spin Crossover Temperature by 100 K
    Feltham, Humphrey L. C.; Johnson, Chloe; Elliott, Anastasia B. S.; Gordon, Keith C.; Albrecht, Martin; Brooker, Sally
    Inorganic Chemistry (2015), 54 (6), 2902-2909CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
    Two new Rdpt ligands featuring long tails, padpt (N-4H-1,2,4-triazole-3,5-di(2-pyridyl)palmitamide) and hpdpt (4-(4-heptadecafluoroctylphenyl)-3,5-bis(2-pyridyl)-4H-1,2,4-triazole), were made and reacted with [FeII(py)4(NCS)2] to give pinkish-red [FeII(padpt)2(SCN)2] (1) and purple-red [FeII(hpdpt)2(SCN)2] (2) as solvent-free crystals. Magnetic measurements reveal that both 1 and 2 exhibit complete and reproducible spin crossovers, with a far lower T1/2 for the amide-alkyl tailed 1 (182 K) than for the fluorocarbon tailed 2 (248 K), which in turn is far lower than the T1/2 of 290 K previously reported for the nonamide-alkyl tailed analog [FeII(C16dpt)2(SCN)2]·2/3H2O (3). Structure detns. for 1 and 2 in both the high spin (HS) and low spin (LS) states confirm the expected trans-NCS conformation and reveal that (a) the tails interdigitate and (b) the LS forms are less distorted than the HS forms (Σ = 58-70° vs. 47-54°). DSC and Raman spectroscopy confirmed the high tail-dependence of the SCO events in 1 and 2, as well as in 3, with the Raman data giving T1/2 values of 190, 243, and 285 K, resp. Bright orange single crystals of the solvatomorph [FeII(hpdpt)2(SCN)2]·MeOH·H2O (2solv) were also structurally and magnetically characterized and, in contrast to 2, found to remain HS down to 4 K, providing further evidence of the huge impact of crystal packing on SCO. Both 1 and 2 form stable Langmuir films at an air-H2O interface, a single layer of which can be transferred to a solid support.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXjs1Ggur0%253D&md5=81627c073d8cda807008d466c44966c0
  9. 9
    Askew, J. H.; Shepherd, H. J. Post-Synthetic Anion Exchange in Iron(II) 1,2,4-Triazole Based Spin Crossover Materials via Mechanochemistry. Dalt. Trans. 2020, 49 (9), 2966– 2971,  DOI: 10.1039/C9DT04700J
    Google Scholar
    There is no corresponding record for this reference.
  10. 10
    Krüger, C.; Augustín, P.; Dlhán̆, L.; Pavlik, J.; Moncol’, J.; Nemec, I.; Boča, R.; Renz, F. Iron(III) Complexes with Pentadentate Schiff-Base Ligands: Influence of Crystal Packing Change and Pseudohalido Coligand Variations on Spin Crossover. Polyhedron 2015, 87, 194– 201,  DOI: 10.1016/j.poly.2014.11.014
    Google Scholar
    10
    Iron(III) complexes with pentadentate Schiff-base ligands: Influence of crystal packing change and pseudohalido coligand variations on spin crossover
    Krueger, Christoph; Augustin, Peter; Dlhan, L'ubor; Pavlik, Jan; Moncol', Jan; Nemec, Ivan; Boca, Roman; Renz, Franz
    Polyhedron (2015), 87 (), 194-201CODEN: PLYHDE; ISSN:0277-5387. (Elsevier Ltd.)
    Two novel Fe(III) complexes involving pentadentate Schiff-base ligands, [Fe(LBr)(L1)], show a gradual temp. induced incomplete spin crossover. While for the L1 = NCSe- coligand the transition temp. (326 K or 317 K) lies above room temp., the N-3 coligand causes its drop down to 143 K or 140 K (two values were obtained by different models). This shift is assocd. with a significant decrease of the enthalpy of the transition from about ΔH = 6.1 kJ mol-1 to ca. ΔH = 1.7 kJ mol-1, while the entropy of the transition is about ΔS = 19 J K-1 mol-1 and ΔS = 12 J K-1 mol-1, resp. Two analogous complexes with Cl- and NCS- coligands remain high-spin over the whole temp. range.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXitVWktb3M&md5=3c6dd9e0d6159d2864d110ec43bc98b3
  11. 11
    Nemec, I.; Herchel, R.; Trávníček, Z. The Relationship between the Strength of Hydrogen Bonding and Spin Crossover Behaviour in a Series of Iron(III) Schiff Base Complexes. Dalt. Trans. 2015, 44 (10), 4474– 4484,  DOI: 10.1039/C4DT03400G
    Google Scholar
    There is no corresponding record for this reference.
  12. 12
    Rajnak, C.; Mičová, R.; Moncol, J.; Dlháň, L.; Krüger, C.; Renz, F.; Boča, R. Spin-Crossover in an Iron(III) Complex Showing a Broad Thermal Hysteresis. Dalton Trans. 2021, 50 (2), 472– 475,  DOI: 10.1039/D0DT03610B
    Google Scholar
    12
    Spin-crossover in an iron(III) complex showing a broad thermal hysteresis
    Rajnak, Cyril; Micova, Romana; Moncol, Jan; Dlhan, Lubor; Kruger, Christoph; Renz, Franz; Boca, Roman
    Dalton Transactions (2021), 50 (2), 472-475CODEN: DTARAF; ISSN:1477-9226. (Royal Society of Chemistry)
    A pentadentate Schiff-base ligand 3,5Cl-L2- and NCSe- form an iron(III) mononuclear complex [Fe(3,5Cl-L)(NCSe)], which shows a thermally induced spin crossover with a broad hysteresis width of 24 K between 123 K (warming) and 99 K (cooling). Analogous complexes of the [Fe(3,5X-L)(Y)] type, where X = Cl or Br and Y = Cl-, N3-, NCS-, and NCSe-, are high-spin over the whole temp. interval.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXisFahsrvK&md5=ca4ac1575c67cb9b3b23e02eb05f9adf
  13. 13
    Boča, R.; Boča, M.; Dlhán̆, L.; Falk, K.; Fuess, H.; Haase, W.; Jaroščiak, R.; Papánková, B.; Renz, F.; Vrbová, M.; Werner, R. Strong Cooperativeness in the Mononuclear Iron(II) Derivative Exhibiting an Abrupt Spin Transition above 400 K. Inorg. Chem. 2001, 40 (13), 3025– 3033,  DOI: 10.1021/ic000807s
    Google Scholar
    13
    Strong Cooperativeness in the Mononuclear Iron(II) Derivative Exhibiting an Abrupt Spin Transition above 400 K
    Boca, R.; Boca, M.; Dlhan, L.; Falk, K.; Fuess, H.; Haase, W.; Jarosciak, R.; Papankova, B.; Renz, F.; Vrbova, M.; Werner, R.
    Inorganic Chemistry (2001), 40 (13), 3025-3033CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
    The spin crossover system, [Fe(bzimpy)2](ClO4)2·0.25H2O, was restudied above room temp. (bzimpy = 2,6-bis(benzimidazol-2-yl)pyridine). The system exhibits an abrupt low-spin to high-spin transition at Tc = 403 K. Liberation of a fractional amt. of water does not affect the spin crossover: the system is perfectly reversible with a hysteresis width of ΔT = 12 K. The existence of the hysteresis at such high temp. dets. that the lowest limit of the solid-state cooperativity parameter is J/k > 403 K despite long iron(II) sepns. (10 Å). The high cooperativeness was assigned to a perfect π-stacking of the benzimidazole rings in the crystal lattice at a distance as short as 3.6 Å. Variable-temp. IR data and the heat capacity measurements match well the magnetic data. The thermodn. properties are ΔH = 17 kJ mol-1, ΔS = 43 J K-1 mol-1, so that the entropy of the spin transition shows a considerable contribution from the mol. vibrations. A theor. model was applied in fitting the magnetic data along the whole hysteresis path. A statistical distribution of the cooperativity parameter led to the feature that angled walls of the hysteresis loop are well reproduced.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3MXjs1Sgt7w%253D&md5=42dc7548049a92d493e79fe6f436ee0f
  14. 14
    Neese, F. Software Update: The ORCA Program System - Version 5.0. WIREs Comput. Mol. Sci. 2022, 12, e1606 DOI: 10.1002/wcms.1606 .
    Google Scholar
    There is no corresponding record for this reference.
  15. 15
    Cirera, J.; Ruiz, E. Assessment of the SCAN Functional for Spin-State Energies in Spin-Crossover Systems. J. Phys. Chem. A 2020, 124 (24), 5053– 5058,  DOI: 10.1021/acs.jpca.0c03758
    Google Scholar
    15
    Assessment of the SCAN Functional for Spin-State Energies in Spin-Crossover Systems
    Cirera, Jordi; Ruiz, Eliseo
    Journal of Physical Chemistry A (2020), 124 (24), 5053-5058CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)
    The strongly constrained and appropriately normed (SCAN) functional has been tested toward the calcn. of spin-state energy differences in a data set of 20 spin-crossover (SCO) systems, ranging from d4 to d7. Results show that the SCAN functional is able to correctly predict the low-spin state as the ground state for all systems, and the energy window provided by the calcns. falls in the approx. range of energies that will allow for SCO to occur. Moreover, the SCAN functional can be used in periodic boundary condition calcns., accounting for the effect of collective crystal vibrations and counterions in the thermochem. of the spin transition. Our results validate this functional as a potential method for in silico screening of new SCO systems at both, mol. and crystal-packed levels.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXhtVWjurrE&md5=9195bec8311eaf38291911baeea0304f
  16. 16
    Cirera, J.; Via-Nadal, M.; Ruiz, E. Benchmarking Density Functional Methods for Calculation of State Energies of First Row Spin-Crossover Molecules. Inorg. Chem. 2018, 57 (22), 14097– 14105,  DOI: 10.1021/acs.inorgchem.8b01821
    Google Scholar
    16
    Benchmarking Density Functional Methods for Calculation of State Energies of First Row Spin-Crossover Molecules
    Cirera, Jordi; Via-Nadal, Mireia; Ruiz, Eliseo
    Inorganic Chemistry (2018), 57 (22), 14097-14105CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
    A systematic study of the performance of several d. functional methodologies to study spin-crossover (SCO) on first row transition metal complexes is reported. All functionals have been tested against several mononuclear systems contg. first row transition metal complexes and exhibiting spin-crossover. Among the tested functionals, the hybrid meta-GGA functional TPSSh with a triple-ζ basis set including polarization functions on all atoms provides the best results across different metals and oxidn. states, and its performance in both predicting the correct ground state and the right energy window for SCO to occur is quite satisfactory. The effect of some addnl. contributions, such as zero-point energies, relativistic effects, and intramol. dispersion interactions, has been analyzed. The reported strategy thus expands the use of the TPSSh functional to other metals and oxidn. states other than FeII, making it the method of choice to study SCO in first row transition metal complexes. Addnl., the presented results validate the potential use of the TPSSh functional for virtual screening of new mols. with SCO, or its use in the study of the electronic structure of such systems.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXitVCrsbfI&md5=dff818a524de459b574a1da49c58cc5d
  17. 17
    Siig, O. S.; Kepp, K. P. Iron(II) and Iron(III) Spin Crossover: Toward an Optimal Density Functional. J. Phys. Chem. A 2018, 122 (16), 4208– 4217,  DOI: 10.1021/acs.jpca.8b02027
    Google Scholar
    17
    Iron(II) and Iron(III) Spin Crossover: Toward an Optimal Density Functional
    Siig, Oliver S.; Kepp, Kasper P.
    Journal of Physical Chemistry A (2018), 122 (16), 4208-4217CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)
    Spin crossover (SCO) plays a major role in biochem., catalysis, materials, and emerging technologies such as mol. electronics and sensors, and thus accurate prediction and design of SCO systems is of high priority. However, the main tool for this purpose, d. functional theory (DFT), is very sensitive to applied methodol. The most abundant SCO systems are Fe(II) and Fe(III) systems. Even with av. good agreement, a functional may be significantly more accurate for Fe(II) or Fe(III) systems, preventing balanced study of SCO candidates of both types. The present work investigates DFT's performance for well-known Fe(II) and Fe(III) SCO complexes, using various design types and customized versions of GGA, hybrid, meta-GGA, meta-hybrid, double-hybrid, and long-range-cor. hybrid functionals. We explore the limits of DFT performance and identify proficient Fe(II)-Fe(III)-balanced functionals. We identify and quantify remarkable differences in the DFT description of Fe(II) and Fe(III) systems. Most functionals become more accurate once Hartree-Fock exchange is adjusted to 10-17%, regardless of the type of functionals involved. However, this typically introduces a clear Fe(II)-Fe(III) bias. The most accurate functionals measured by mean abs. errors <10 kJ/mol are CAMB3LYP-17, B3LYP*, and B97-15 with 15-17% Hartree-Fock exchange, closely followed by CAMB3LYP and CAMB3LYP-15, OPBE, rPBE-10, and B3P86-15. While GGA functionals display a small Fe(II)-Fe(III) bias, they are generally inaccurate, except the O exchange functional. Hybrid functionals (including B2PLYP double hybrids and meta hybrids) tend to favor HS too much in Fe(II) vs. Fe(III), which is important in many studies where the oxidn. state of iron can vary, e.g. rational SCO design and studies of catalytic processes involving iron. The only functional with a combined bias <5 kJ/mol and a decent MAE (15 kJ/mol) is our customized PBE0-12 functional. Alternatively one has to sacrifice Fe(II)-Fe(III) balance to use the best functionals for each group sep. We also investigated the precision (measured as the std. deviation of errors) and show that the target accuracy for iron SCO is 10 kJ/mol for accuracy and 5 kJ/mol for precision, and DFT is probably not going to break this limit in the near future. Importantly, all four types of functional behavior (accurate/precise, accurate/imprecise, inaccurate/precise, inaccurate/imprecise) are obsd. More generally, our work illustrates the importance not only of overall accuracy but also of balanced accuracy for systems likely to occur in context.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXnt1agtbc%253D&md5=0d91ee09bb56e1d9af094b6f065e3782
  18. 18
    Perdew, J. P.; Burke, K.; Ernzerhof, M. Generalized Gradient Approximation Made Simple. Phys. Rev. Lett. 1996, 77 (18), 3865– 3868,  DOI: 10.1103/PhysRevLett.77.3865
    Google Scholar
    18
    Generalized gradient approximation made simple
    Perdew, John P.; Burke, Kieron; Ernzerhof, Matthias
    Physical Review Letters (1996), 77 (18), 3865-3868CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)
    Generalized gradient approxns. (GGA's) for the exchange-correlation energy improve upon the local spin d. (LSD) description of atoms, mols., and solids. We present a simple derivation of a simple GGA, in which all parameters (other than those in LSD) are fundamental consts. Only general features of the detailed construction underlying the Perdew-Wang 1991 (PW91) GGA are invoked. Improvements over PW91 include an accurate description of the linear response of the uniform electron gas, correct behavior under uniform scaling, and a smoother potential.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK28XmsVCgsbs%253D&md5=55943538406ee74f93aabdf882cd4630
  19. 19
    Furness, J. W.; Kaplan, A. D.; Ning, J.; Perdew, J. P.; Sun, J. Accurate and Numerically Efficient r 2 SCAN Meta-Generalized Gradient Approximation. J. Phys. Chem. Lett. 2020, 11 (19), 8208– 8215,  DOI: 10.1021/acs.jpclett.0c02405
    Google Scholar
    19
    Accurate and Numerically Efficient r2SCAN Meta-Generalized Gradient Approximation
    Furness, James W.; Kaplan, Aaron D.; Ning, Jinliang; Perdew, John P.; Sun, Jianwei
    Journal of Physical Chemistry Letters (2020), 11 (19), 8208-8215CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)
    The recently proposed rSCAN functional [J. Chem. Phys., 2019, 150, 161101] is a regularized form of the SCAN functional [Phys. Rev. Lett., 2015, 115, 036402] that improves SCAN's numerical performance at the expense of breaking constraints known from the exact exchange-correlation functional. We construct a new meta-generalized gradient approxn. by restoring exact constraint adherence to rSCAN. The resulting functional maintains rSCAN's numerical performance while restoring the transferable accuracy of SCAN.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXhslequ77N&md5=49adb31d49e1e53910d87275f6400ae9
  20. 20
    Reiher, M. Theoretical Study of the Fe(Phen)2(NCS)2 Spin-Crossover Complex with Reparametrized Density Functionals. Inorg. Chem. 2002, 41 (25), 6928– 6935,  DOI: 10.1021/ic025891l
    Google Scholar
    20
    Theoretical Study of the Fe(phen)2(NCS)2 Spin-Crossover Complex with Reparametrized Density Functionals
    Reiher, Markus
    Inorganic Chemistry (2002), 41 (25), 6928-6935CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
    The theor. study of spin-crossover compds. is very challenging as those parts of the exptl. findings that concern the electronic structure of these compds. can currently hardly be reproduced because of either tech. limitations of highly accurate ab initio methods or because of inaccuracies of d. functional methods in the prediction of low-spin/high-spin energy splitting. However, calcns. with reparametrized d. functionals on mols. of the thermal spin-crossover type can give improved results when compared with expt. for close-lying states of different spin and are therefore important for, e.g., transition metal catalysis. A classification of transition metal compds. within hybrid d. functional theory is given to distinguish std., crit., and complicated cases. From the class of complicated cases we choose the prominent spin-crossover compd. Fe(phen)2(NCS)2 and show in a first step how the electronic contribution to the energy splitting can be calcd. In a second step, the vibrational effects on the spin flip are investigated within the harmonic force-field approxn. of the isolated-mol. approach. A main result of the study is the necessity of exact-exchange redn. in hybrid d. functionals to arrive at reasonable electronic energy splittings. The study resolves problems that originated from the use of std. d. functionals, which are not able to reproduce the electronic contribution to the low-spin/high-spin splitting correctly, and demonstrates to which extent reparametrized d. functionals can be used for the prediction of the spin-crossover effect.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD38Xoslaqtbw%253D&md5=ebc3252d68752bf1a679792f21010774
  21. 21
    Caldeweyher, E.; Ehlert, S.; Hansen, A.; Neugebauer, H.; Spicher, S.; Bannwarth, C.; Grimme, S. A Generally Applicable Atomic-Charge Dependent London Dispersion Correction. J. Chem. Phys. 2019, 150 (15), 154122,  DOI: 10.1063/1.5090222
    Google Scholar
    21
    A generally applicable atomic-charge dependent London dispersion correction
    Caldeweyher, Eike; Ehlert, Sebastian; Hansen, Andreas; Neugebauer, Hagen; Spicher, Sebastian; Bannwarth, Christoph; Grimme, Stefan
    Journal of Chemical Physics (2019), 150 (15), 154122/1-154122/19CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)
    The so-called D4 model is presented for the accurate computation of London dispersion interactions in d. functional theory approxns. (DFT-D4) and generally for atomistic modeling methods. In this successor to the DFT-D3 model, the at. coordination-dependent dipole polarizabilities are scaled based on at. partial charges which can be taken from various sources. For this purpose, a new charge-dependent parameter-economic scaling function is designed. Classical charges are obtained from an at. electronegativity equilibration procedure for which efficient anal. derivs. with respect to nuclear positions are developed. A numerical Casimir-Polder integration of the atom-in-mol. dynamic polarizabilities then yields charge- and geometry-dependent dipole-dipole dispersion coeffs. Similar to the D3 model, the dynamic polarizabilities are precomputed by time-dependent DFT and all elements up to radon (Z = 86) are covered. The two-body dispersion energy expression has the usual sum-over-atom-pairs form and includes dipole-dipole as well as dipole-quadrupole interactions. For a benchmark set of 1225 mol. dipole-dipole dispersion coeffs., the D4 model achieves an unprecedented accuracy with a mean relative deviation of 3.8% compared to 4.7% for D3. In addn. to the two-body part, three-body effects are described by an Axilrod-Teller-Muto term. A common many-body dispersion expansion was extensively tested, and an energy correction based on D4 polarizabilities is found to be advantageous for larger systems. Becke-Johnson-type damping parameters for DFT-D4 are detd. for more than 60 common d. functionals. For various std. energy benchmark sets, DFT-D4 slightly but consistently outperforms DFT-D3. Esp. for metal contg. systems, the introduced charge dependence of the dispersion coeffs. improves thermochem. properties. We suggest (DFT-)D4 as a phys. improved and more sophisticated dispersion model in place of DFT-D3 for DFT calcns. as well as other low-cost approaches like semi-empirical models. (c) 2019 American Institute of Physics.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXot1SrsL0%253D&md5=c125347db9048016461dbcec3f8bb21f
  22. 22
    Garcia-Ratés, M.; Neese, F. Effect of the Solute Cavity on the Solvation Energy and Its Derivatives within the Framework of the Gaussian Charge Scheme. J. Comput. Chem. 2020, 41 (9), 922– 939,  DOI: 10.1002/jcc.26139
    Google Scholar
    22
    Effect of the Solute Cavity on the Solvation Energy and its Derivatives within the Framework of the Gaussian Charge Scheme
    Garcia-Rates, Miquel; Neese, Frank
    Journal of Computational Chemistry (2020), 41 (9), 922-939CODEN: JCCHDD; ISSN:0192-8651. (John Wiley & Sons, Inc.)
    The treatment of the solvation charges using Gaussian functions in the polarizable continuum model results in a smooth potential energy surface. These charges are placed on top of the surface of the solute cavity. In this article, we study the effect of the solute cavity (van der Waals-type or solvent-excluded surface-type) using the Gaussian charge scheme within the framework of the conductor-like polarizable continuum model on (a) the accuracy and computational cost of the SCF (SCF) energy and its gradient and on (b) the calcn. of free energies of solvation. For that purpose, we have considered a large set of systems ranging from few atoms to \>200 atoms in different solvents. Our results at the DFT level using the B3LYP functional and the def2-TZVP basis set show that the choice of the solute cavity does neither affect the accuracy nor the cost of calcns. for small systems (< 100 atoms). For larger systems, the use of a vdW-type cavity is recommended, as it prevents small oscillations in the gradient (present when using a SES-type cavity), which affect the convergence of the SCF energy gradient. Regarding the free energies of solvation, we consider a solvent-dependent probe sphere to construct the solvent-accessible surface area required to calc. the nonelectrostatic contribution to the free energy of solvation. For this part, our results for a large set of org. mols. in different solvents agree with available exptl. data with an accuracy lower than 1 kcal/mol for both polar and nonpolar solvents.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXitVSjtQ%253D%253D&md5=9cbadf36de956b915990a85f1f4c0a78
  23. 23
    Barone, V.; Cossi, M. Quantum Calculation of Molecular Energies and Energy Gradients in Solution by a Conductor Solvent Model. J. Phys. Chem. A 1998, 102 (11), 1995– 2001,  DOI: 10.1021/jp9716997
    Google Scholar
    23
    Quantum Calculation of Molecular Energies and Energy Gradients in Solution by a Conductor Solvent Model
    Barone, Vincenzo; Cossi, Maurizio
    Journal of Physical Chemistry A (1998), 102 (11), 1995-2001CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)
    A new implementation of the conductor-like screening solvation model (COSMO) in the GAUSSIAN94 package is presented. It allows Hartree-Fock (HF), d. functional (DF) and post-HF energy, and HF and DF gradient calcns.: the cavities are modeled on the mol. shape, using recently optimized parameters, and both electrostatic and nonelectrostatic contributions to energies and gradients are considered. The calcd. solvation energies for 19 neutral mols. in water are found in very good agreement with exptl. data; the solvent-induced geometry relaxation is studied for some closed and open shell mols., at HF and DF levels. The computational times are very satisfying: the self-consistent energy evaluation needs a time 15-30% longer than the corresponding procedure in vacuo, whereas the calcn. of energy gradients is only 25% longer than in vacuo for medium size mols.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1cXht1Cgt7o%253D&md5=7fe7f5f4627f26fd16a34e25219efaa6
  24. 24
    Lakhloufi, S.; Tailleur, E.; Guo, W.; Le Gac, F.; Marchivie, M.; Lemée-Cailleau, M.-H.; Chastanet, G.; Guionneau, P. Mosaicity of Spin-Crossover Crystals. Crystals 2018, 8 (9), 363,  DOI: 10.3390/cryst8090363
    Google Scholar
    24
    Mosaicity of spin-crossover crystals
    Lakhloufi, Sabine; Tailleur, Elodie; Guo, Wenbin; Le Gac, Frederic; Marchivie, Mathieu; Lemee-Cailleau, Marie-Helene; Chastanet, Guillaume; Guionneau, Philippe
    Crystals (2018), 8 (9), 363/1-363/10CODEN: CRYSBC; ISSN:2073-4352. (MDPI AG)
    Real crystals are composed of a mosaic of domains whose misalignment is evaluated by their level of "mosaicity" using X-ray diffraction. In thermo-induced spin-crossover compds., the crystal may be seen as a mixt. of metal centers, some being in the high-spin (HS) state and others in the low spin (LS) state. Since the vol. of HS and LS crystal packings are known to be very different, the assembly of domains within the crystal, i.e., its mosaicity, may be modified at the spin crossover. With little data available in the literature we propose an investigation into the temp. dependence of mosaicity in certain spin-crossover crystals. The study was preceded by the examn. of instrumental factors, in order to establish a protocol for the measurement of mosaicity. The results show that crystal mosaicity appears to be strongly modified by thermal spin-crossover; however, the nature of the changes are probably sample dependent and driven, or masked, in most cases by the characteristics of the crystal (disorder, morphol. ...). No general relationship could be established between mosaicity and crystal properties. If, however, mosaicity studies in spin-crossover crystals are conducted and interpreted with great care, they could help to elucidate crucial crystal characteristics such as mech. fatigability, and more generally to investigate systems where phase transition is assocd. with large vol. changes.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXitVWgurjJ&md5=aa5979bcbdb7700958ab31cd2ca93b64
  25. 25
    CrysAlisPro, 1.171.42.49; Rigaku Oxford Diffraction, 2020.
    Google Scholar
    There is no corresponding record for this reference.
  26. 26
    Harrison, K.; Wu, Z.; Juers, D. H. A Comparison of Gas Stream Cooling and Plunge Cooling of Macromolecular Crystals. J. Appl. Crystallogr. 2019, 52 (5), 1222– 1232,  DOI: 10.1107/S1600576719010318
    Google Scholar
    26
    A comparison of gas stream cooling and plunge cooling of macromolecular crystals
    Harrison, Kaitlin; Wu, Zhenguo; Juers, Douglas H.
    Journal of Applied Crystallography (2019), 52 (5), 1222-1232CODEN: JACGAR; ISSN:1600-5767. (International Union of Crystallography)
    Cryocooling for macromol. crystallog. is usually performed via plunging the crystal into a liq. cryogen or placing the crystal in a cold gas stream. These two approaches are compared here for the case of nitrogen cooling. The results show that gas stream cooling, which typically cools the crystal more slowly, yields lower mosaicity and, in some cases, a stronger anomalous signal relative to rapid plunge cooling. During plunging, moving the crystal slowly through the cold gas layer above the liq. surface can produce mosaicity similar to gas stream cooling. Annealing plunge cooled crystals by warming and recooling in the gas stream allows the mosaicity and anomalous signal to recover. For tetragonal thermolysin, the obsd. effects are less pronounced when the cryosolvent has smaller thermal contraction, under which conditions the protein structures from plunge cooled and gas stream cooled crystals are very similar. Finally, this work also demonstrates that the resoln. dependence of the reflecting range is correlated with the cooling method, suggesting it may be a useful tool for discerning whether crystals are cooled too rapidly. The results support previous studies suggesting that slower cooling methods are less deleterious to crystal order, as long as ice formation is prevented and dehydration is limited.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhvFWrsLbJ&md5=bfa4653601f67659f2a0449cba2aa413
  27. 27
    Kabsch, W. Integration, Scaling, Space-Group Assignment and Post-Refinement. Acta Crystallogr. Sect. D Biol. Crystallogr. 2010, 66 (2), 133– 144,  DOI: 10.1107/S0907444909047374
    Google Scholar
    27
    Integration, scaling, space-group assignment and post-refinement
    Kabsch, Wolfgang
    Acta Crystallographica, Section D: Biological Crystallography (2010), 66 (2), 133-144CODEN: ABCRE6; ISSN:0907-4449. (International Union of Crystallography)
    Important steps in the processing of rotation data are described that are common to most software packages. These programs differ in the details and in the methods implemented to carry out the tasks. Here, the working principles underlying the data-redn. package XDS are explained, including the new features of automatic detn. of spot size and reflecting range, recognition and assignment of crystal symmetry and a highly efficient algorithm for the detn. of correction/scaling factors.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXhs1Sisb4%253D&md5=eb1db34f3c959b4921771eb9f57b2159
  28. 28
    Madsen, S. R.; Overgaard, J.; Stalke, D.; Iversen, B. B. High-Pressure Single Crystal X-Ray Diffraction Study of the Linear Metal Chain Compound Co3(Dpa)4Br2·CH2Cl2. Dalt. Trans. 2015, 44 (19), 9038– 9043,  DOI: 10.1039/C5DT00447K
    Google Scholar
    There is no corresponding record for this reference.
  29. 29
    Farley, C.; Burks, G.; Siegert, T.; Juers, D. H. Improved Reproducibility of Unit-Cell Parameters in Macromolecular Cryocrystallography by Limiting Dehydration during Crystal Mounting. Acta Crystallogr. Sect. D Biol. Crystallogr. 2014, 70 (8), 2111– 2124,  DOI: 10.1107/S1399004714012310
    Google Scholar
    29
    Improved reproducibility of unit-cell parameters in macromolecular cryocrystallography by limiting dehydration during crystal mounting
    Farley, Christopher; Burks, Geoffry; Siegert, Thomas; Juers, Douglas H.
    Acta Crystallographica, Section D: Biological Crystallography (2014), 70 (8), 2111-2124CODEN: ABCRE6; ISSN:1399-0047. (International Union of Crystallography)
    In macromol. cryocrystallog. unit-cell parameters can have low reproducibility, limiting the effectiveness of combining data sets from multiple crystals and inhibiting the development of defined repeatable cooling protocols. Here, potential sources of unit-cell variation are investigated and crystal dehydration during loop-mounting is found to be an important factor. The amt. of water lost by the unit cell depends on the crystal size, the loop size, the ambient relative humidity and the transfer distance to the cooling medium. To limit water loss during crystal mounting, a threefold strategy has been implemented. Firstly, crystal manipulations are performed in a humid environment similar to the humidity of the crystal-growth or soaking soln. Secondly, the looped crystal is transferred to a vial contg. a small amt. of the crystal soaking soln. Upon loop transfer, the vial is sealed, which allows transport of the crystal at its equilibrated humidity. Thirdly, the crystal loop is directly mounted from the vial into the cold gas stream. This strategy minimizes the exposure of the crystal to relatively low humidity ambient air, improves the reproducibility of low-temp. unit-cell parameters and offers some new approaches to crystal handling and cryoprotection.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXht1Git73F&md5=cd7e13be5754b5af27276e8e86fa6f45

Cited By

Click to copy section linkSection link copied!
Citation Statements
Explore this article's citation statements on scite.ai
powered by  Scite

This article is cited by 1 publications.

  1. Theerapoom Boonprab, Warisa Thammasangwan, Guillaume Chastanet, Mathieu Gonidec, Phimphaka Harding, David J. Harding. Halide Anion Effects and Magnetostructural Relationships in Iron(III) Spin Crossover Complexes. Crystal Growth & Design 2024, 24 (19) , 8145-8152. https://doi.org/10.1021/acs.cgd.4c01068
Download PDF
Go to Crystal Growth & Design
Get e-Alerts
Get e-Alerts

Crystal Growth & Design

Cite this: Cryst. Growth Des. 2023, 23, 3, 1323–1329
Click to copy citationCitation copied!
https://doi.org/10.1021/acs.cgd.2c01411
Published February 16, 2023

Copyright © 2023 American Chemical Society. This publication is licensed under

CC-BY 4.0 .

Article Views

997

Altmetric

-

Citations

1
Learn about these metrics

Article Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.

Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.

The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated.

  • Abstract

    High Resolution Image
    Download MS PowerPoint Slide

    Figure 1

    Figure 1. Temperature dependence of μeff/μB for 1_Φ1 and 1_Φ1p.

    High Resolution Image
    Download MS PowerPoint Slide

    Figure 2

    Figure 2. Temperature dependence of μeff/μB for 1_Φ0.25 (top) and the temperature dependence of the selected unit cell parameters as determined from the single crystal X-ray diffraction experiment for 1_Φ0.25 (bottom).

    High Resolution Image
    Download MS PowerPoint Slide

    Figure 3

    Figure 3. Temperature dependence the high-spin molar fraction xHS according to ISM (top), the ISM parameters (middle), and transition temperatures (bottom) for crystalline samples of 1.

    High Resolution Image
    Download MS PowerPoint Slide

    Figure 4

    Figure 4. Graphical comparison of the donor–acceptor bond distances between X-ray data (dotted lines) and the respective DFT methods (B3LYP*, OPBE, and r2SCAN) for the high-spin state of 1.

    High Resolution Image
    Download MS PowerPoint Slide

    Figure 5

    Figure 5. Graphical comparison the energy difference corrected by the zero-temperature vibrational energy from the frequency calculation ΔEel+ZPE between the HS and LS states for different DFT methods applied to 1.

    High Resolution Image
    Download MS PowerPoint Slide

    Figure 6

    Figure 6. Plot of T1/2↓ versus crystallization rate (A). The colored boxes are used to highlight the crystallization rate, with a lighter color indicating slower crystallization. The plots of Rint vs T1/2↓ (B), e3 vs T1/2↓ (C), and eavg vs T1/2↓ (D). The value of eavg was calculated as the arithmetic average of components e1, e2, and e3. In all plots, the T1/2↓ value of crystals that remained in the high spin phase down to 80 K was assigned as 70 K for visualization purposes.

    High Resolution Image
    Download MS PowerPoint Slide

  • References

    This article references 29 other publications.

    1. 1
      Bari, R. A.; Sivardière, J. Low-Spin-High-Spin Transitions in Transition-Metal-Ion Compounds. Phys. Rev. B 1972, 5 (11), 4466– 4471,  DOI: 10.1103/PhysRevB.5.4466
      There is no corresponding record for this reference.
    2. 2
      Wajnflasz, J. Etude de La Transition “Low Spin”-“High Spin” Dans Les Complexes Octaédriques d’ion de Transition. Phys. status solidi 1970, 40 (2), 537– 545,  DOI: 10.1002/pssb.19700400212
      2
      "Low-spin"-"high-spin" transition in transition ion octahedral complexes
      Wajnflasz, J.
      Physica Status Solidi (1970), 40 (2), 537-45CODEN: PHSSAK; ISSN:0031-8957.
      Some 6-coordinated transition-ion complexes show an abnormal variation of the no. of Bohr magnetons with temp. These complexes have 2 stable equil. states simultaneously characterized by 2 different ionic radii and by fundamental states of a few hundred degrees Kelvin apart, which belong to 2 different representations. The cryst. fields assocd. with these 2 equil. states are on both sides of Δπ, the mean pairing energy. An Ising model with an interaction between neighboring transition ions can explain the magnetic behavior of these complexes and delimit an area of existence of a first-order transition between "low-spin" and "high-spin" states.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaE3cXkvFWnt7Y%253D&md5=bba310f775ebac7608c32590fe630cfe
    3. 3
      Boča, R.; Linert, W. Is There a Need for New Models of the Spin Crossover? In Molecular Magnets Recent Highlights; Springer Vienna: Vienna, 2002; pp 83– 100 DOI: 10.1007/978-3-7091-6018-3_6 .
      There is no corresponding record for this reference.
    4. 4
      Shakirova, O. G.; Lavrenova, L. G.; Kurat’eva, N. V.; Naumov, D. Y.; Daletskii, V. A.; Sheludyakova, L. A.; Logvinenko, V. A.; Vasilevskii, S. F. Spin Crossover in Iron(II) Complexes with Tris(Pyrazol-1-Yl)Methane. Russ. J. Coord. Chem. 2010, 36 (4), 275– 283,  DOI: 10.1134/S1070328410040068
      4
      Spin crossover in iron(II) complexes with tris(pyrazol-1-yl)methane
      Shakirova, O. G.; Lavrenova, L. G.; Kurat'eva, N. V.; Naumov, D. Yu.; Daletskii, V. A.; Sheludyakova, L. A.; Logvinenko, V. A.; Vasilevskii, S. F.
      Russian Journal of Coordination Chemistry (2010), 36 (4), 275-283CODEN: RJCCEY; ISSN:1070-3284. (Pleiades Publishing, Ltd.)
      Mononuclear iron(II) coordination compds. with tris(pyrazol-1-yl)methane (HC(Pz)3) described as [Fe{HC(Pz)3}2]A2.nH2O, [A = Cl-, Br-, I-, 1/2 SO2-4, n = 0-7] were synthesized. The compds. were studied by static magnetic susceptibility measurements, IR and UV/Vis spectroscopy, and powder X-ray diffraction. The crystal and mol. structures of all compds. were detd. by single crystal X-ray diffraction.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXlsVyjsLk%253D&md5=464456bfb6fafd609256baa551a83717
    5. 5
      Halcrow, M. A. Structure:Function Relationships in Molecular Spin-Crossover Complexes. Chem. Soc. Rev. 2011, 40 (7), 4119,  DOI: 10.1039/c1cs15046d
      5
      Structure:function relationships in molecular spin-crossover complexes
      Halcrow, Malcolm A.
      Chemical Society Reviews (2011), 40 (7), 4119-4142CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
      A review. Spin-crossover compds. are becoming increasingly popular for device and sensor applications, and in soft materials, that make use of their switchable color, paramagnetism and cond. The de novo design of new solid spin-crossover compds. with pre-defined switching properties is desirable for application purposes. This challenging problem of crystal engineering requires an understanding of how the temp. and cooperativity of a spin-transition are influenced by the structure of the bulk material. Towards that end, this crit. review presents a survey of mol. spin-crossover compds. with good availability of crystallog. data. A picture is emerging that changes in mol. shape between the high- and low-spin states, and the ability of a lattice to accommodate such changes, can play an important role in detg. the existence and the cooperativity of a thermal spin-transition in the solid state (198 refs.).
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXns12msrc%253D&md5=2a525c09d4f8ac62d2d305af3b4d8f36
    6. 6
      Roubeau, O. Triazole-Based One-Dimensional Spin-Crossover Coordination Polymers. Chem. - A Eur. J. 2012, 18 (48), 15230– 15244,  DOI: 10.1002/chem.201201647
      6
      Triazole-Based One-Dimensional Spin-Crossover Coordination Polymers
      Roubeau, Olivier
      Chemistry - A European Journal (2012), 18 (48), 15230-15244CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)
      A review. One-dimensional coordination FeII polymers constructed through triple N1,N2-1,2,4-triazole bridges form a unique class of spin-crossover materials, the synthetic versatility of which allows tuning the spin-crossover properties, the design of gels, films, liq. crystals, and nanoparticles and single-particle addressing. This Minireview provides the 1st complete overview of these very attractive switchable materials and their most recent developments.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38Xhs1agtbbN&md5=3e4be5c36be98a60071085372aff6a43
    7. 7
      Arcis-Castíllo, Z.; Zheng, S.; Siegler, M. A.; Roubeau, O.; Bedoui, S.; Bonnet, S. Tuning the Transition Temperature and Cooperativity of Bapbpy-Based Mononuclear Spin-Crossover Compounds: Interplay between Molecular and Crystal Engineering. Chem. - A Eur. J. 2011, 17 (52), 14826– 14836,  DOI: 10.1002/chem.201101301
      7
      Tuning the Transition Temperature and Cooperativity of bapbpy-Based Mononuclear Spin-Crossover Compounds: Interplay between Molecular and Crystal Engineering
      Arcis-Castillo, Zulema; Zheng, Sipeng; Siegler, Maxime A.; Roubeau, Olivier; Bedoui, Salma; Bonnet, Sylvestre
      Chemistry - A European Journal (2011), 17 (52), 14826-14836CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)
      (1) Different isomers of the same mononuclear iron(II) complex give materials with different spin-crossover (hereafter SCO) properties, and (2) minor modifications of the bapbpy (bapbpy = N6,N6'-di(pyridin-2-yl)-2,2'-bipyridine-6,6'-diamine) ligand allows SCO to be obtained near room temp. The authors also provide a qual. model to understand the link between the structure of bapbpy-based ligands and the SCO properties of their iron(II) compds. Thus, seven new trans-[Fe{R2(bapbpy)}(NCS)2] compds. were prepd., in which the R2bapbpy ligand bears picoline (9-12), quin-2-oline (13), isoquin-3-oline (14), or isoquin-1-oline (15) substituents. From this series, three compds. (12, 14, and 15) have SCO properties, one of which (15) occurs at 288 K. The crystal structures of 11, 12, and 15 show that the intermol. interactions in these materials are similar to those found in the parent compd. [Fe(bapbpy)(NCS)2] (1), in which each iron complex interacts with its neighbors through weak N-H···S hydrogen bonding and π-π stacking. For 12 and 15, hindering groups located near the N-H bridges weaken the N-S intermol. interactions, which is correlated to non-cooperative SCO. For 14, the substitution is further away from the N-H bridges, and the SCO remains cooperative as in 1 with a hysteresis cycle. Optical microscopy photographs show the strikingly different spatio-temporal evolution of the phase transition in the noncooperative SCO compd. 12 relative to that found in 1. Heat-capacity measurements were made for 1, 12, 14, and 15 and fitted to the Sorai domain model. The no. n of like-spin SCO centers per interacting domain, which is related to the cooperativity of the spin transition, was found high for 1 and 14 and low for 12 and 15. Finally, although both pairs of 11/12 and 14/15 are pairs of isomers their SCO properties are surprisingly different.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXhsFGrsr%252FM&md5=b6ccb49019aa18666ad0e556ba7d85ac
    8. 8
      Feltham, H. L. C.; Johnson, C.; Elliott, A. B. S.; Gordon, K. C.; Albrecht, M.; Brooker, S. “Tail” Tuning of Iron(II) Spin Crossover Temperature by 100 K. Inorg. Chem. 2015, 54 (6), 2902– 2909,  DOI: 10.1021/ic503040f
      8
      "Tail" Tuning of Iron(II) Spin Crossover Temperature by 100 K
      Feltham, Humphrey L. C.; Johnson, Chloe; Elliott, Anastasia B. S.; Gordon, Keith C.; Albrecht, Martin; Brooker, Sally
      Inorganic Chemistry (2015), 54 (6), 2902-2909CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
      Two new Rdpt ligands featuring long tails, padpt (N-4H-1,2,4-triazole-3,5-di(2-pyridyl)palmitamide) and hpdpt (4-(4-heptadecafluoroctylphenyl)-3,5-bis(2-pyridyl)-4H-1,2,4-triazole), were made and reacted with [FeII(py)4(NCS)2] to give pinkish-red [FeII(padpt)2(SCN)2] (1) and purple-red [FeII(hpdpt)2(SCN)2] (2) as solvent-free crystals. Magnetic measurements reveal that both 1 and 2 exhibit complete and reproducible spin crossovers, with a far lower T1/2 for the amide-alkyl tailed 1 (182 K) than for the fluorocarbon tailed 2 (248 K), which in turn is far lower than the T1/2 of 290 K previously reported for the nonamide-alkyl tailed analog [FeII(C16dpt)2(SCN)2]·2/3H2O (3). Structure detns. for 1 and 2 in both the high spin (HS) and low spin (LS) states confirm the expected trans-NCS conformation and reveal that (a) the tails interdigitate and (b) the LS forms are less distorted than the HS forms (Σ = 58-70° vs. 47-54°). DSC and Raman spectroscopy confirmed the high tail-dependence of the SCO events in 1 and 2, as well as in 3, with the Raman data giving T1/2 values of 190, 243, and 285 K, resp. Bright orange single crystals of the solvatomorph [FeII(hpdpt)2(SCN)2]·MeOH·H2O (2solv) were also structurally and magnetically characterized and, in contrast to 2, found to remain HS down to 4 K, providing further evidence of the huge impact of crystal packing on SCO. Both 1 and 2 form stable Langmuir films at an air-H2O interface, a single layer of which can be transferred to a solid support.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXjs1Ggur0%253D&md5=81627c073d8cda807008d466c44966c0
    9. 9
      Askew, J. H.; Shepherd, H. J. Post-Synthetic Anion Exchange in Iron(II) 1,2,4-Triazole Based Spin Crossover Materials via Mechanochemistry. Dalt. Trans. 2020, 49 (9), 2966– 2971,  DOI: 10.1039/C9DT04700J
      There is no corresponding record for this reference.
    10. 10
      Krüger, C.; Augustín, P.; Dlhán̆, L.; Pavlik, J.; Moncol’, J.; Nemec, I.; Boča, R.; Renz, F. Iron(III) Complexes with Pentadentate Schiff-Base Ligands: Influence of Crystal Packing Change and Pseudohalido Coligand Variations on Spin Crossover. Polyhedron 2015, 87, 194– 201,  DOI: 10.1016/j.poly.2014.11.014
      10
      Iron(III) complexes with pentadentate Schiff-base ligands: Influence of crystal packing change and pseudohalido coligand variations on spin crossover
      Krueger, Christoph; Augustin, Peter; Dlhan, L'ubor; Pavlik, Jan; Moncol', Jan; Nemec, Ivan; Boca, Roman; Renz, Franz
      Polyhedron (2015), 87 (), 194-201CODEN: PLYHDE; ISSN:0277-5387. (Elsevier Ltd.)
      Two novel Fe(III) complexes involving pentadentate Schiff-base ligands, [Fe(LBr)(L1)], show a gradual temp. induced incomplete spin crossover. While for the L1 = NCSe- coligand the transition temp. (326 K or 317 K) lies above room temp., the N-3 coligand causes its drop down to 143 K or 140 K (two values were obtained by different models). This shift is assocd. with a significant decrease of the enthalpy of the transition from about ΔH = 6.1 kJ mol-1 to ca. ΔH = 1.7 kJ mol-1, while the entropy of the transition is about ΔS = 19 J K-1 mol-1 and ΔS = 12 J K-1 mol-1, resp. Two analogous complexes with Cl- and NCS- coligands remain high-spin over the whole temp. range.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXitVWktb3M&md5=3c6dd9e0d6159d2864d110ec43bc98b3
    11. 11
      Nemec, I.; Herchel, R.; Trávníček, Z. The Relationship between the Strength of Hydrogen Bonding and Spin Crossover Behaviour in a Series of Iron(III) Schiff Base Complexes. Dalt. Trans. 2015, 44 (10), 4474– 4484,  DOI: 10.1039/C4DT03400G
      There is no corresponding record for this reference.
    12. 12
      Rajnak, C.; Mičová, R.; Moncol, J.; Dlháň, L.; Krüger, C.; Renz, F.; Boča, R. Spin-Crossover in an Iron(III) Complex Showing a Broad Thermal Hysteresis. Dalton Trans. 2021, 50 (2), 472– 475,  DOI: 10.1039/D0DT03610B
      12
      Spin-crossover in an iron(III) complex showing a broad thermal hysteresis
      Rajnak, Cyril; Micova, Romana; Moncol, Jan; Dlhan, Lubor; Kruger, Christoph; Renz, Franz; Boca, Roman
      Dalton Transactions (2021), 50 (2), 472-475CODEN: DTARAF; ISSN:1477-9226. (Royal Society of Chemistry)
      A pentadentate Schiff-base ligand 3,5Cl-L2- and NCSe- form an iron(III) mononuclear complex [Fe(3,5Cl-L)(NCSe)], which shows a thermally induced spin crossover with a broad hysteresis width of 24 K between 123 K (warming) and 99 K (cooling). Analogous complexes of the [Fe(3,5X-L)(Y)] type, where X = Cl or Br and Y = Cl-, N3-, NCS-, and NCSe-, are high-spin over the whole temp. interval.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXisFahsrvK&md5=ca4ac1575c67cb9b3b23e02eb05f9adf
    13. 13
      Boča, R.; Boča, M.; Dlhán̆, L.; Falk, K.; Fuess, H.; Haase, W.; Jaroščiak, R.; Papánková, B.; Renz, F.; Vrbová, M.; Werner, R. Strong Cooperativeness in the Mononuclear Iron(II) Derivative Exhibiting an Abrupt Spin Transition above 400 K. Inorg. Chem. 2001, 40 (13), 3025– 3033,  DOI: 10.1021/ic000807s
      13
      Strong Cooperativeness in the Mononuclear Iron(II) Derivative Exhibiting an Abrupt Spin Transition above 400 K
      Boca, R.; Boca, M.; Dlhan, L.; Falk, K.; Fuess, H.; Haase, W.; Jarosciak, R.; Papankova, B.; Renz, F.; Vrbova, M.; Werner, R.
      Inorganic Chemistry (2001), 40 (13), 3025-3033CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
      The spin crossover system, [Fe(bzimpy)2](ClO4)2·0.25H2O, was restudied above room temp. (bzimpy = 2,6-bis(benzimidazol-2-yl)pyridine). The system exhibits an abrupt low-spin to high-spin transition at Tc = 403 K. Liberation of a fractional amt. of water does not affect the spin crossover: the system is perfectly reversible with a hysteresis width of ΔT = 12 K. The existence of the hysteresis at such high temp. dets. that the lowest limit of the solid-state cooperativity parameter is J/k > 403 K despite long iron(II) sepns. (10 Å). The high cooperativeness was assigned to a perfect π-stacking of the benzimidazole rings in the crystal lattice at a distance as short as 3.6 Å. Variable-temp. IR data and the heat capacity measurements match well the magnetic data. The thermodn. properties are ΔH = 17 kJ mol-1, ΔS = 43 J K-1 mol-1, so that the entropy of the spin transition shows a considerable contribution from the mol. vibrations. A theor. model was applied in fitting the magnetic data along the whole hysteresis path. A statistical distribution of the cooperativity parameter led to the feature that angled walls of the hysteresis loop are well reproduced.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3MXjs1Sgt7w%253D&md5=42dc7548049a92d493e79fe6f436ee0f
    14. 14
      Neese, F. Software Update: The ORCA Program System - Version 5.0. WIREs Comput. Mol. Sci. 2022, 12, e1606 DOI: 10.1002/wcms.1606 .
      There is no corresponding record for this reference.
    15. 15
      Cirera, J.; Ruiz, E. Assessment of the SCAN Functional for Spin-State Energies in Spin-Crossover Systems. J. Phys. Chem. A 2020, 124 (24), 5053– 5058,  DOI: 10.1021/acs.jpca.0c03758
      15
      Assessment of the SCAN Functional for Spin-State Energies in Spin-Crossover Systems
      Cirera, Jordi; Ruiz, Eliseo
      Journal of Physical Chemistry A (2020), 124 (24), 5053-5058CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)
      The strongly constrained and appropriately normed (SCAN) functional has been tested toward the calcn. of spin-state energy differences in a data set of 20 spin-crossover (SCO) systems, ranging from d4 to d7. Results show that the SCAN functional is able to correctly predict the low-spin state as the ground state for all systems, and the energy window provided by the calcns. falls in the approx. range of energies that will allow for SCO to occur. Moreover, the SCAN functional can be used in periodic boundary condition calcns., accounting for the effect of collective crystal vibrations and counterions in the thermochem. of the spin transition. Our results validate this functional as a potential method for in silico screening of new SCO systems at both, mol. and crystal-packed levels.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXhtVWjurrE&md5=9195bec8311eaf38291911baeea0304f
    16. 16
      Cirera, J.; Via-Nadal, M.; Ruiz, E. Benchmarking Density Functional Methods for Calculation of State Energies of First Row Spin-Crossover Molecules. Inorg. Chem. 2018, 57 (22), 14097– 14105,  DOI: 10.1021/acs.inorgchem.8b01821
      16
      Benchmarking Density Functional Methods for Calculation of State Energies of First Row Spin-Crossover Molecules
      Cirera, Jordi; Via-Nadal, Mireia; Ruiz, Eliseo
      Inorganic Chemistry (2018), 57 (22), 14097-14105CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
      A systematic study of the performance of several d. functional methodologies to study spin-crossover (SCO) on first row transition metal complexes is reported. All functionals have been tested against several mononuclear systems contg. first row transition metal complexes and exhibiting spin-crossover. Among the tested functionals, the hybrid meta-GGA functional TPSSh with a triple-ζ basis set including polarization functions on all atoms provides the best results across different metals and oxidn. states, and its performance in both predicting the correct ground state and the right energy window for SCO to occur is quite satisfactory. The effect of some addnl. contributions, such as zero-point energies, relativistic effects, and intramol. dispersion interactions, has been analyzed. The reported strategy thus expands the use of the TPSSh functional to other metals and oxidn. states other than FeII, making it the method of choice to study SCO in first row transition metal complexes. Addnl., the presented results validate the potential use of the TPSSh functional for virtual screening of new mols. with SCO, or its use in the study of the electronic structure of such systems.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXitVCrsbfI&md5=dff818a524de459b574a1da49c58cc5d
    17. 17
      Siig, O. S.; Kepp, K. P. Iron(II) and Iron(III) Spin Crossover: Toward an Optimal Density Functional. J. Phys. Chem. A 2018, 122 (16), 4208– 4217,  DOI: 10.1021/acs.jpca.8b02027
      17
      Iron(II) and Iron(III) Spin Crossover: Toward an Optimal Density Functional
      Siig, Oliver S.; Kepp, Kasper P.
      Journal of Physical Chemistry A (2018), 122 (16), 4208-4217CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)
      Spin crossover (SCO) plays a major role in biochem., catalysis, materials, and emerging technologies such as mol. electronics and sensors, and thus accurate prediction and design of SCO systems is of high priority. However, the main tool for this purpose, d. functional theory (DFT), is very sensitive to applied methodol. The most abundant SCO systems are Fe(II) and Fe(III) systems. Even with av. good agreement, a functional may be significantly more accurate for Fe(II) or Fe(III) systems, preventing balanced study of SCO candidates of both types. The present work investigates DFT's performance for well-known Fe(II) and Fe(III) SCO complexes, using various design types and customized versions of GGA, hybrid, meta-GGA, meta-hybrid, double-hybrid, and long-range-cor. hybrid functionals. We explore the limits of DFT performance and identify proficient Fe(II)-Fe(III)-balanced functionals. We identify and quantify remarkable differences in the DFT description of Fe(II) and Fe(III) systems. Most functionals become more accurate once Hartree-Fock exchange is adjusted to 10-17%, regardless of the type of functionals involved. However, this typically introduces a clear Fe(II)-Fe(III) bias. The most accurate functionals measured by mean abs. errors <10 kJ/mol are CAMB3LYP-17, B3LYP*, and B97-15 with 15-17% Hartree-Fock exchange, closely followed by CAMB3LYP and CAMB3LYP-15, OPBE, rPBE-10, and B3P86-15. While GGA functionals display a small Fe(II)-Fe(III) bias, they are generally inaccurate, except the O exchange functional. Hybrid functionals (including B2PLYP double hybrids and meta hybrids) tend to favor HS too much in Fe(II) vs. Fe(III), which is important in many studies where the oxidn. state of iron can vary, e.g. rational SCO design and studies of catalytic processes involving iron. The only functional with a combined bias <5 kJ/mol and a decent MAE (15 kJ/mol) is our customized PBE0-12 functional. Alternatively one has to sacrifice Fe(II)-Fe(III) balance to use the best functionals for each group sep. We also investigated the precision (measured as the std. deviation of errors) and show that the target accuracy for iron SCO is 10 kJ/mol for accuracy and 5 kJ/mol for precision, and DFT is probably not going to break this limit in the near future. Importantly, all four types of functional behavior (accurate/precise, accurate/imprecise, inaccurate/precise, inaccurate/imprecise) are obsd. More generally, our work illustrates the importance not only of overall accuracy but also of balanced accuracy for systems likely to occur in context.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXnt1agtbc%253D&md5=0d91ee09bb56e1d9af094b6f065e3782
    18. 18
      Perdew, J. P.; Burke, K.; Ernzerhof, M. Generalized Gradient Approximation Made Simple. Phys. Rev. Lett. 1996, 77 (18), 3865– 3868,  DOI: 10.1103/PhysRevLett.77.3865
      18
      Generalized gradient approximation made simple
      Perdew, John P.; Burke, Kieron; Ernzerhof, Matthias
      Physical Review Letters (1996), 77 (18), 3865-3868CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)
      Generalized gradient approxns. (GGA's) for the exchange-correlation energy improve upon the local spin d. (LSD) description of atoms, mols., and solids. We present a simple derivation of a simple GGA, in which all parameters (other than those in LSD) are fundamental consts. Only general features of the detailed construction underlying the Perdew-Wang 1991 (PW91) GGA are invoked. Improvements over PW91 include an accurate description of the linear response of the uniform electron gas, correct behavior under uniform scaling, and a smoother potential.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK28XmsVCgsbs%253D&md5=55943538406ee74f93aabdf882cd4630
    19. 19
      Furness, J. W.; Kaplan, A. D.; Ning, J.; Perdew, J. P.; Sun, J. Accurate and Numerically Efficient r 2 SCAN Meta-Generalized Gradient Approximation. J. Phys. Chem. Lett. 2020, 11 (19), 8208– 8215,  DOI: 10.1021/acs.jpclett.0c02405
      19
      Accurate and Numerically Efficient r2SCAN Meta-Generalized Gradient Approximation
      Furness, James W.; Kaplan, Aaron D.; Ning, Jinliang; Perdew, John P.; Sun, Jianwei
      Journal of Physical Chemistry Letters (2020), 11 (19), 8208-8215CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)
      The recently proposed rSCAN functional [J. Chem. Phys., 2019, 150, 161101] is a regularized form of the SCAN functional [Phys. Rev. Lett., 2015, 115, 036402] that improves SCAN's numerical performance at the expense of breaking constraints known from the exact exchange-correlation functional. We construct a new meta-generalized gradient approxn. by restoring exact constraint adherence to rSCAN. The resulting functional maintains rSCAN's numerical performance while restoring the transferable accuracy of SCAN.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXhslequ77N&md5=49adb31d49e1e53910d87275f6400ae9
    20. 20
      Reiher, M. Theoretical Study of the Fe(Phen)2(NCS)2 Spin-Crossover Complex with Reparametrized Density Functionals. Inorg. Chem. 2002, 41 (25), 6928– 6935,  DOI: 10.1021/ic025891l
      20
      Theoretical Study of the Fe(phen)2(NCS)2 Spin-Crossover Complex with Reparametrized Density Functionals
      Reiher, Markus
      Inorganic Chemistry (2002), 41 (25), 6928-6935CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
      The theor. study of spin-crossover compds. is very challenging as those parts of the exptl. findings that concern the electronic structure of these compds. can currently hardly be reproduced because of either tech. limitations of highly accurate ab initio methods or because of inaccuracies of d. functional methods in the prediction of low-spin/high-spin energy splitting. However, calcns. with reparametrized d. functionals on mols. of the thermal spin-crossover type can give improved results when compared with expt. for close-lying states of different spin and are therefore important for, e.g., transition metal catalysis. A classification of transition metal compds. within hybrid d. functional theory is given to distinguish std., crit., and complicated cases. From the class of complicated cases we choose the prominent spin-crossover compd. Fe(phen)2(NCS)2 and show in a first step how the electronic contribution to the energy splitting can be calcd. In a second step, the vibrational effects on the spin flip are investigated within the harmonic force-field approxn. of the isolated-mol. approach. A main result of the study is the necessity of exact-exchange redn. in hybrid d. functionals to arrive at reasonable electronic energy splittings. The study resolves problems that originated from the use of std. d. functionals, which are not able to reproduce the electronic contribution to the low-spin/high-spin splitting correctly, and demonstrates to which extent reparametrized d. functionals can be used for the prediction of the spin-crossover effect.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD38Xoslaqtbw%253D&md5=ebc3252d68752bf1a679792f21010774
    21. 21
      Caldeweyher, E.; Ehlert, S.; Hansen, A.; Neugebauer, H.; Spicher, S.; Bannwarth, C.; Grimme, S. A Generally Applicable Atomic-Charge Dependent London Dispersion Correction. J. Chem. Phys. 2019, 150 (15), 154122,  DOI: 10.1063/1.5090222
      21
      A generally applicable atomic-charge dependent London dispersion correction
      Caldeweyher, Eike; Ehlert, Sebastian; Hansen, Andreas; Neugebauer, Hagen; Spicher, Sebastian; Bannwarth, Christoph; Grimme, Stefan
      Journal of Chemical Physics (2019), 150 (15), 154122/1-154122/19CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)
      The so-called D4 model is presented for the accurate computation of London dispersion interactions in d. functional theory approxns. (DFT-D4) and generally for atomistic modeling methods. In this successor to the DFT-D3 model, the at. coordination-dependent dipole polarizabilities are scaled based on at. partial charges which can be taken from various sources. For this purpose, a new charge-dependent parameter-economic scaling function is designed. Classical charges are obtained from an at. electronegativity equilibration procedure for which efficient anal. derivs. with respect to nuclear positions are developed. A numerical Casimir-Polder integration of the atom-in-mol. dynamic polarizabilities then yields charge- and geometry-dependent dipole-dipole dispersion coeffs. Similar to the D3 model, the dynamic polarizabilities are precomputed by time-dependent DFT and all elements up to radon (Z = 86) are covered. The two-body dispersion energy expression has the usual sum-over-atom-pairs form and includes dipole-dipole as well as dipole-quadrupole interactions. For a benchmark set of 1225 mol. dipole-dipole dispersion coeffs., the D4 model achieves an unprecedented accuracy with a mean relative deviation of 3.8% compared to 4.7% for D3. In addn. to the two-body part, three-body effects are described by an Axilrod-Teller-Muto term. A common many-body dispersion expansion was extensively tested, and an energy correction based on D4 polarizabilities is found to be advantageous for larger systems. Becke-Johnson-type damping parameters for DFT-D4 are detd. for more than 60 common d. functionals. For various std. energy benchmark sets, DFT-D4 slightly but consistently outperforms DFT-D3. Esp. for metal contg. systems, the introduced charge dependence of the dispersion coeffs. improves thermochem. properties. We suggest (DFT-)D4 as a phys. improved and more sophisticated dispersion model in place of DFT-D3 for DFT calcns. as well as other low-cost approaches like semi-empirical models. (c) 2019 American Institute of Physics.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXot1SrsL0%253D&md5=c125347db9048016461dbcec3f8bb21f
    22. 22
      Garcia-Ratés, M.; Neese, F. Effect of the Solute Cavity on the Solvation Energy and Its Derivatives within the Framework of the Gaussian Charge Scheme. J. Comput. Chem. 2020, 41 (9), 922– 939,  DOI: 10.1002/jcc.26139
      22
      Effect of the Solute Cavity on the Solvation Energy and its Derivatives within the Framework of the Gaussian Charge Scheme
      Garcia-Rates, Miquel; Neese, Frank
      Journal of Computational Chemistry (2020), 41 (9), 922-939CODEN: JCCHDD; ISSN:0192-8651. (John Wiley & Sons, Inc.)
      The treatment of the solvation charges using Gaussian functions in the polarizable continuum model results in a smooth potential energy surface. These charges are placed on top of the surface of the solute cavity. In this article, we study the effect of the solute cavity (van der Waals-type or solvent-excluded surface-type) using the Gaussian charge scheme within the framework of the conductor-like polarizable continuum model on (a) the accuracy and computational cost of the SCF (SCF) energy and its gradient and on (b) the calcn. of free energies of solvation. For that purpose, we have considered a large set of systems ranging from few atoms to \>200 atoms in different solvents. Our results at the DFT level using the B3LYP functional and the def2-TZVP basis set show that the choice of the solute cavity does neither affect the accuracy nor the cost of calcns. for small systems (< 100 atoms). For larger systems, the use of a vdW-type cavity is recommended, as it prevents small oscillations in the gradient (present when using a SES-type cavity), which affect the convergence of the SCF energy gradient. Regarding the free energies of solvation, we consider a solvent-dependent probe sphere to construct the solvent-accessible surface area required to calc. the nonelectrostatic contribution to the free energy of solvation. For this part, our results for a large set of org. mols. in different solvents agree with available exptl. data with an accuracy lower than 1 kcal/mol for both polar and nonpolar solvents.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXitVSjtQ%253D%253D&md5=9cbadf36de956b915990a85f1f4c0a78
    23. 23
      Barone, V.; Cossi, M. Quantum Calculation of Molecular Energies and Energy Gradients in Solution by a Conductor Solvent Model. J. Phys. Chem. A 1998, 102 (11), 1995– 2001,  DOI: 10.1021/jp9716997
      23
      Quantum Calculation of Molecular Energies and Energy Gradients in Solution by a Conductor Solvent Model
      Barone, Vincenzo; Cossi, Maurizio
      Journal of Physical Chemistry A (1998), 102 (11), 1995-2001CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)
      A new implementation of the conductor-like screening solvation model (COSMO) in the GAUSSIAN94 package is presented. It allows Hartree-Fock (HF), d. functional (DF) and post-HF energy, and HF and DF gradient calcns.: the cavities are modeled on the mol. shape, using recently optimized parameters, and both electrostatic and nonelectrostatic contributions to energies and gradients are considered. The calcd. solvation energies for 19 neutral mols. in water are found in very good agreement with exptl. data; the solvent-induced geometry relaxation is studied for some closed and open shell mols., at HF and DF levels. The computational times are very satisfying: the self-consistent energy evaluation needs a time 15-30% longer than the corresponding procedure in vacuo, whereas the calcn. of energy gradients is only 25% longer than in vacuo for medium size mols.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1cXht1Cgt7o%253D&md5=7fe7f5f4627f26fd16a34e25219efaa6
    24. 24
      Lakhloufi, S.; Tailleur, E.; Guo, W.; Le Gac, F.; Marchivie, M.; Lemée-Cailleau, M.-H.; Chastanet, G.; Guionneau, P. Mosaicity of Spin-Crossover Crystals. Crystals 2018, 8 (9), 363,  DOI: 10.3390/cryst8090363
      24
      Mosaicity of spin-crossover crystals
      Lakhloufi, Sabine; Tailleur, Elodie; Guo, Wenbin; Le Gac, Frederic; Marchivie, Mathieu; Lemee-Cailleau, Marie-Helene; Chastanet, Guillaume; Guionneau, Philippe
      Crystals (2018), 8 (9), 363/1-363/10CODEN: CRYSBC; ISSN:2073-4352. (MDPI AG)
      Real crystals are composed of a mosaic of domains whose misalignment is evaluated by their level of "mosaicity" using X-ray diffraction. In thermo-induced spin-crossover compds., the crystal may be seen as a mixt. of metal centers, some being in the high-spin (HS) state and others in the low spin (LS) state. Since the vol. of HS and LS crystal packings are known to be very different, the assembly of domains within the crystal, i.e., its mosaicity, may be modified at the spin crossover. With little data available in the literature we propose an investigation into the temp. dependence of mosaicity in certain spin-crossover crystals. The study was preceded by the examn. of instrumental factors, in order to establish a protocol for the measurement of mosaicity. The results show that crystal mosaicity appears to be strongly modified by thermal spin-crossover; however, the nature of the changes are probably sample dependent and driven, or masked, in most cases by the characteristics of the crystal (disorder, morphol. ...). No general relationship could be established between mosaicity and crystal properties. If, however, mosaicity studies in spin-crossover crystals are conducted and interpreted with great care, they could help to elucidate crucial crystal characteristics such as mech. fatigability, and more generally to investigate systems where phase transition is assocd. with large vol. changes.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXitVWgurjJ&md5=aa5979bcbdb7700958ab31cd2ca93b64
    25. 25
      CrysAlisPro, 1.171.42.49; Rigaku Oxford Diffraction, 2020.
      There is no corresponding record for this reference.
    26. 26
      Harrison, K.; Wu, Z.; Juers, D. H. A Comparison of Gas Stream Cooling and Plunge Cooling of Macromolecular Crystals. J. Appl. Crystallogr. 2019, 52 (5), 1222– 1232,  DOI: 10.1107/S1600576719010318
      26
      A comparison of gas stream cooling and plunge cooling of macromolecular crystals
      Harrison, Kaitlin; Wu, Zhenguo; Juers, Douglas H.
      Journal of Applied Crystallography (2019), 52 (5), 1222-1232CODEN: JACGAR; ISSN:1600-5767. (International Union of Crystallography)
      Cryocooling for macromol. crystallog. is usually performed via plunging the crystal into a liq. cryogen or placing the crystal in a cold gas stream. These two approaches are compared here for the case of nitrogen cooling. The results show that gas stream cooling, which typically cools the crystal more slowly, yields lower mosaicity and, in some cases, a stronger anomalous signal relative to rapid plunge cooling. During plunging, moving the crystal slowly through the cold gas layer above the liq. surface can produce mosaicity similar to gas stream cooling. Annealing plunge cooled crystals by warming and recooling in the gas stream allows the mosaicity and anomalous signal to recover. For tetragonal thermolysin, the obsd. effects are less pronounced when the cryosolvent has smaller thermal contraction, under which conditions the protein structures from plunge cooled and gas stream cooled crystals are very similar. Finally, this work also demonstrates that the resoln. dependence of the reflecting range is correlated with the cooling method, suggesting it may be a useful tool for discerning whether crystals are cooled too rapidly. The results support previous studies suggesting that slower cooling methods are less deleterious to crystal order, as long as ice formation is prevented and dehydration is limited.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhvFWrsLbJ&md5=bfa4653601f67659f2a0449cba2aa413
    27. 27
      Kabsch, W. Integration, Scaling, Space-Group Assignment and Post-Refinement. Acta Crystallogr. Sect. D Biol. Crystallogr. 2010, 66 (2), 133– 144,  DOI: 10.1107/S0907444909047374
      27
      Integration, scaling, space-group assignment and post-refinement
      Kabsch, Wolfgang
      Acta Crystallographica, Section D: Biological Crystallography (2010), 66 (2), 133-144CODEN: ABCRE6; ISSN:0907-4449. (International Union of Crystallography)
      Important steps in the processing of rotation data are described that are common to most software packages. These programs differ in the details and in the methods implemented to carry out the tasks. Here, the working principles underlying the data-redn. package XDS are explained, including the new features of automatic detn. of spot size and reflecting range, recognition and assignment of crystal symmetry and a highly efficient algorithm for the detn. of correction/scaling factors.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXhs1Sisb4%253D&md5=eb1db34f3c959b4921771eb9f57b2159
    28. 28
      Madsen, S. R.; Overgaard, J.; Stalke, D.; Iversen, B. B. High-Pressure Single Crystal X-Ray Diffraction Study of the Linear Metal Chain Compound Co3(Dpa)4Br2·CH2Cl2. Dalt. Trans. 2015, 44 (19), 9038– 9043,  DOI: 10.1039/C5DT00447K
      There is no corresponding record for this reference.
    29. 29
      Farley, C.; Burks, G.; Siegert, T.; Juers, D. H. Improved Reproducibility of Unit-Cell Parameters in Macromolecular Cryocrystallography by Limiting Dehydration during Crystal Mounting. Acta Crystallogr. Sect. D Biol. Crystallogr. 2014, 70 (8), 2111– 2124,  DOI: 10.1107/S1399004714012310
      29
      Improved reproducibility of unit-cell parameters in macromolecular cryocrystallography by limiting dehydration during crystal mounting
      Farley, Christopher; Burks, Geoffry; Siegert, Thomas; Juers, Douglas H.
      Acta Crystallographica, Section D: Biological Crystallography (2014), 70 (8), 2111-2124CODEN: ABCRE6; ISSN:1399-0047. (International Union of Crystallography)
      In macromol. cryocrystallog. unit-cell parameters can have low reproducibility, limiting the effectiveness of combining data sets from multiple crystals and inhibiting the development of defined repeatable cooling protocols. Here, potential sources of unit-cell variation are investigated and crystal dehydration during loop-mounting is found to be an important factor. The amt. of water lost by the unit cell depends on the crystal size, the loop size, the ambient relative humidity and the transfer distance to the cooling medium. To limit water loss during crystal mounting, a threefold strategy has been implemented. Firstly, crystal manipulations are performed in a humid environment similar to the humidity of the crystal-growth or soaking soln. Secondly, the looped crystal is transferred to a vial contg. a small amt. of the crystal soaking soln. Upon loop transfer, the vial is sealed, which allows transport of the crystal at its equilibrated humidity. Thirdly, the crystal loop is directly mounted from the vial into the cold gas stream. This strategy minimizes the exposure of the crystal to relatively low humidity ambient air, improves the reproducibility of low-temp. unit-cell parameters and offers some new approaches to crystal handling and cryoprotection.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXht1Git73F&md5=cd7e13be5754b5af27276e8e86fa6f45

  • Supporting Information

    Supporting Information

    The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.cgd.2c01411.

    • Synthesis, crystallographic data, magnetic measurements, DFT calculation details, and powder diffraction patterns (PDF)

    Accession Codes

    CCDC 1909057 and 2223462–2223463 contain 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.


    Terms & Conditions

    Most electronic Supporting Information files are available without a subscription to ACS Web Editions. Such files may be downloaded by article for research use (if there is a public use license linked to the relevant article, that license may permit other uses). Permission may be obtained from ACS for other uses through requests via the RightsLink permission system: http://pubs.acs.org/page/copyright/permissions.html.