Phosphonate monoesters are atypical linkers for metal–organic frameworks, but they offer potentially added versatility. In this work, a bulky isopropyl ester is used to direct the topology of a copper(II) network from a dense to an open framework, CALF-30. CALF-30 shows no adsorption of N₂ or CH₄ however, using CO₂ sorption, CALF-30 was found to have a Langmuir surface area of over 300 m²/g and to be stable to conditions of 90% relative humidity at 353 K owing to kinetic shielding of the framework by the phosphonate ester.

Investigations on the transformation of selenidostannates in ionic liquids were extended by using ternary P1-type cluster precursors [M₄Sn₄Se₁₇]^10– [M = Mn (1), Zn (2), Cd (3)], which were synthesized for the first time as their Cs⁺ salts. Treatment of 1 with 1,2-diaminoethane (en) in [BMIm][BF₄] yielded two-dimensional-layered [Mn(en)_2.5(en-Me)_0.5][Sn₃Se₇] (4; en-Me = H₂NC₂H₄NHCH₃). 1–4 were characterized by single-crystal X-ray diffraction and UV/visible spectroscopy.

We demonstrate a facile and general approach for the fabrication of highly dispersed Au, Pd, and Pt nanoparticles (NPs) on MIL-125(Ti) without using extra reducing and capping agents. Noble-metal NP formation is directed by an in situ redox reaction between the reductive MIL-125(Ti) with Ti³⁺ and oxidative metal salt precursors. The resulting composites function as efficient photocatalysts.

In the presence of “Ag₂O” as a promoter, γ-MnO₂ traps dihydrogen in its (2 × 1) and (1 × 1) tunnels. The course of this reaction was examined by analyzing the X-ray diffraction patterns of the H_xMnO₂/“Ag₂O” system (0 ≤ x < 1) on the basis of pair distribution function and density functional theory (DFT) analyses. Hydrogen trapping occurs preferentially in the (2 × 1) tunnels of γ-MnO₂, which is then followed by that in the (1 × 1) tunnels. Our DFT analysis shows that this process is thermodynamically favorable.

A modular synthetic approach is reported for the synthesis of heterometallic metal–organic complex arrays (MOCAs). Modules of four metal centers containing three different metals copper(II), nickel(II), platinum(II), or ruthenium(II) are prepared using a solid-phase polypeptide synthesis technique and then linked in solution to make MOCAs of eight metal centers as linear, T-branched, and H-branched compounds. The MOCA molecular topologies thus have specific unique linear and branched sequences of metals along the peptide backbone.

To examine the steric effect of the phosphorus substituents in cyclodiphosphazanes, two less sterically demanding alkynyl-functionalized cis-[(μ-N^tBuP)₂(C≡CPh)₂] (1) and trans-[(μ-N^tBuP)₂(C≡CPh)₂] (2) were synthesized. The cis isomer 1, with a large subtending angle (135.8°) upon treatment with [Rh(CO)₂Cl]₂, afforded the first rhodium(I) cyclic pentameric macrocycle [Rh(CO)Cl{(μ-N^tBuP)₂(C≡CPh)₂}]₅ (3). The crystal structure of the cyclic pentamer 3 closely resembles a classical “Ferris wheel”.

Ab initio methods have been used to explore the unexpectedly strong magnetic anisotropy and the magnetostructural correlations in mononuclear eight-coordinate complex [Co^II(12-crown-4)₂]²⁺. Our calculations showed that both decreasing α and increasing φ may enhance its magnetic anisotropy, which was rationalized by the qualitative theory proposed by Long and co-workers. Moreover, we deduced that the |D| value of [Co^II(12-crown-4)₂]²⁺ with α = 52° and φ = 43° is the largest one.

Two cyano- and phenoxo-bridged hexanuclear Ni^II₂Dy^III₂Fe^III₂ (1) and octanuclear Ni^II₄Dy^III₂Fe^III₂ (2) trimetallic cyclic complexes have been obtained. They are the first trimetallic metallocycles. Magnetic studies reveal that 1 and 2 exhibit single-molecule-magnet behavior with an energy barrier of 17.9 K for complex 1 in a 2000 Oe static field and 25.0 K for complex 2 in a zero static field.

Two novel organic–inorganic hybrid frameworks containing multiarylpolycarboxylate linkers and cobalt phosphate layers, [H₂DABCO]·[Co(HPO₄)(bpdc)] (1) and [H₂DABCO]₃·[Co₁₀(npa)₃(PO₄)₆Cl₂] (2), where bpdc = 4,4′-biphenyldicarboxylate, npa = 2,6-naphthalenedicarboxylate, and DABCO = 1,4-diazabicyclo[2.2.2]octane, have been solvothermally synthesized. Compound 1 features a 3D zeolite-like supramolecular network with ABW topology, and compound 2 is a 3D framework structure with unusual I²O² connectivity.

The principle of the Irving–Williams series is applied to the design of a novel prodrug based on K₂Zn₃[Fe(CN)₆]₂ nanoparticles (ZnPB NPs) for Wilson’s disease (WD), a rare but fatal genetic disorder characterized by the accumulation of excess copper in the liver and other vital organs. The predetermined ion-exchange reaction rather than chelation between ZnPB NPs and copper ions leads to high selectivity of such NPs for copper in the presence of the other endogenous metal ions. Furthermore, ZnPB NPs are highly water-dispersible and noncytotoxic and can be readily internalized by cells to target intracellular copper ions for selective copper detoxification, suggesting their potential application as a new-generation treatment for WD.

Polyanionic cluster [β-As₈V₁₄O₄₂(H₂O)]^4– is well embedded in a large porous eight-membered cationic ring of the copper ligand, giving a stable host–guest supramolecular system. The assembly exhibits an efficient heterogeneous catalytic performance for the reduction of Cr^VI using formic acid at ambient temperature.

We report the proton conduction properties of a 2D flexible MOF and a 1D coordination polymer having the molecular formulas {[Zn(C₁₀H₂O₈)_0.5(C₁₀S₂N₂H₈)]·5H₂O]}_n (1) and {[Zn(C₁₀H₂O₈)_0.5(C₁₀S₂N₂H₈)]·2H₂O]}_n (2), respectively. Compounds 1 and 2 show high conductivity values of 2.55 × 10^–7 and 4.39 × 10^–4 S cm^–1 at 80 °C and 95% RH. The conductivity value of compound 1 is in the range of those for previously reported flexible MOFs, and compound 2 shows the highest proton conductivity among the carboxylate-based 1D CPs. The dimensionality and the internal hydrogen bonding connectivity play a vital role in the resultant conductivity. Variable-temperature experiments of both compounds at high humidity reveal that the conductivity values increase with increasing temperature, whereas the variable humidity studies signify the influence of relative humidity on high-temperature proton conductivity. The time-dependent measurements for both compounds demonstrate their ability to retain conductivity up to 10 h.

A thoroughly mechanistic investigation on the [Cp₂Mo(OH)(OH₂)]⁺-catalyzed hydrolysis of ethyl acetate has been performed using density functional theory methodology together with continuum and discrete–continuum solvation models. The use of explicit water molecules in the PCM-B3LYP/aug-cc-pVTZ (aug-cc-pVTZ-PP for Mo)//PCM-B3LYP/aug-cc-pVDZ (aug-cc-pVDZ-PP for Mo) computations is crucial to show that the intramolecular hydroxo ligand attack is the preferred mechanism in agreement with experimental suggestions. Besides, the most stable intermediate located along this mechanism is analogous to that experimentally reported for the norbornenyl acetate hydrolysis catalyzed by molybdocenes. The three most relevant steps are the formation and cleavage of the tetrahedral intermediate immediately formed after the hydroxo ligand attack and the acetic acid formation, with the second one being the rate-determining step with a Gibbs energy barrier of 36.7 kcal/mol. Among several functionals checked, B3LYP-D3 and M06 give the best agreement with experiment as the rate-determining Gibbs energy barrier obtained only differs 0.2 and 0.7 kcal/mol, respectively, from that derived from the experimental kinetic constant measured at 296.15 K. In both cases, the acetic acid elimination becomes now the rate-determining step of the overall process as it is 0.4 kcal/mol less stable than the tetrahedral intermediate cleavage. Apart from clarifying the identity of the cyclic intermediate and discarding the tetrahedral intermediate formation as the rate-determining step for the mechanism of the acetyl acetate hydrolysis catalyzed by molybdocenes, the small difference in the Gibbs energy barrier found between the acetic acid formation and the tetrahedral intermediate cleavage also uncovers that the rate-determining step could change when studying the reactivity of carboxylic esters other than ethyl acetate substrate specific toward molybdocenes or other transition metal complexes. Therefore, in general, the information reported here could be of interest in designing new catalysts and understanding the reaction mechanism of these and other metal-catalyzed hydrolysis reactions.

Separation of trivalent actinides (An(III)) from trivalent lanthanides (Ln(III)) is a challenging task because of the nearly identical chemical properties of these groups. Diethylenetriaminepentaacetate (DTPA), a key reagent used in the TALSPEAK process that effectively separates An(III) from Ln(III), is believed to play a critical role in the An(III)/Ln(III) separation. However, the underlying principles for the separation based on the difference in the complexation of DTPA with An(III) and Ln(III) remain unclear. In this work, the complexation of DTPA with Cm(III) at 10–70 °C was investigated by spectrophotometry, luminescence spectroscopy, and microcalorimetry, in conjunction with computational methods. The binding strength, the enthalpy of complexation, the coordination modes, and the luminescence properties are compared between the Cm(III)–DTPA and Eu(III)–DTPA systems. The experimental and computational data demonstrated that the difference between Cm(III) and Eu(III) in the binding strength with DTPA can be attributed to the stronger covalence bonding between Cm(III) and the nitrogen donors of DTPA.

The ambient pressure phase of silicon disulfide (NP-SiS₂), published in 1935, is orthorhombic and contains chains of distorted, edge-sharing SiS₄ tetrahedra. The first high pressure phase, HP3-SiS₂, published in 1965 and quenchable to ambient conditions, is tetragonal and contains distorted corner-sharing SiS₄ tetrahedra. Here, we report on the crystal structures of two monoclinic phases, HP1-SiS₂ and HP2-SiS₂, which can be considered as missing links between the orthorhombic and the tetragonal phase. Both monoclinic phases contain edge- as well as corner-sharing SiS₄ tetrahedra. With increasing pressure, the volume contraction (−ΔV/V) and the density, compared to the orthorhombic NP-phase, increase from only edge-sharing tetrahedra to only corner-sharing tetrahedra. The lattice and the positional parameters of NP-SiS₂, HP1-SiS₂, HP2-SiS₂, and HP3-SiS₂ were derived in good agreement with the experimental data from group–subgroup relationships with the CaF₂ structure as aristotype. In addition, the Raman spectra of SiS₂ show that the most intense bands of the new phases HP1-SiS₂ and HP2-SiS₂ (408 and 404 cm^–1, respectively) lie between those of NP-SiS₂ (434 cm^–1) and HP3-SiS₂ (324 cm^–1). Density functional theory (DFT) calculations confirm these observations.

The reaction between 4,4′-sulfonyldibenzoic acid (H₂SDBA) and manganese under mild conditions resulted in the isolation of two new three-dimensional compounds, [Mn₄(C₁₄H₈O₆S)₄(DMA)₂]·3DMA, I, and [Mn₃(C₁₄H₈O₆S)₃(DMA)₂(MeOH)]·DMA, IIa. Both structures have Mn₃ trimer oxo cluster units. While the Mn₃ oxoclusters are connected through octahedral manganese forming one-dimensional Mn–O–Mn chains in I, the Mn₃ units are isolated in IIa. The SDBA units connect the Mn–O–Mn chains and the Mn₃ clusters giving rise to the three-dimensional structure. Both compounds have coordinated and free solvent molecules. In IIa, two different solvent molecules are coordinated, of which one solvent can be reversibly exchanged by a variety of other similar solvents via a solvent-mediated single crystal to single crystal (SCSC) transformation. The free lattice DMA solvent molecules in I can be exchanged by water molecules resulting in hydrophilic channels. Proton conductivity studies on I reveals a high proton mobility with conductivity values of ∼0.87 × 10^–3 Ω^–1 cm^–1 at 34 °C and 98% RH, which is comparable to some of the good proton conductivity values observed in inorganic coordination polymers. We have also shown structural transformation of I to IIa through a possible dissolution and recrystallization pathway. In addition, both I and IIa appear to transform to two other manganese compounds [H₃O][Mn₃(μ₃-OH)(C₁₄H₈O₆S)₃(H₂O)](DMF)₅ and [H₃O]₂[Mn₇(μ₃-OH)₄(C₁₄H₈O₆S)₆(H₂O)₄](H₂O)₂(DMF)₈ under suitable reaction conditions. We have partially substituted Co in place of Mn in the Mn₃ trimer clusters forming [CoMn₂(C₁₄H₈O₆S)₃(DMA)₂(EtOH)]·DMA, III, a structure that is closely related to IIa. All the compounds reveal antiferromagnetic behavior. On heating, the cobalt substituted phase (compound III) forms a CoMn₂O₄ spinel phase with particle sizes in the nanometer range.

A redox-active diamine ligand, 4,4′-bis(di-p-anisylamino)-2,2′-bipyridine (NNbpy), has been prepared. Electrochemical and spectroscopic studies suggest that little electronic coupling is present between two amine groups in NNbpy. After chelation with Ru(bpy)₂ (bpy is 2,2′-bipyridine), the resulting complex displays two N^•+/0 processes at +1.02 and +1.16 V versus Ag/AgCl. In the mixed-valent state, rich near-infrared absorptions have been observed, which are believed to consist of multiple metal-to-ligand charge transfer and intervalence charge transfer transitions in the low-energy region. These results suggest that the amine–amine electronic coupling has been enhanced by chelation with Ru(bpy)₂. In contrast, no efficient electronic coupling can be realized by chelation with Ir(ppy)₂ (ppy is 2′-phenylpyridine) or Re(CO)₃Cl. A ruthenium ion-mediated electron transfer mechanism, instead of through-space coupling, has been proposed to explain this phenomenon. For the purpose of comparison, a monoamine-substituted bpy ligand and corresponding Ru(bpy)₂ complex have been synthesized and studied. In addition, EPR, DFT, and TDDFT studies have been performed to complement the experimental results.

Herein, Ca K-edge X-ray absorption spectroscopy (XAS) is developed as a means to characterize the local environment of calcium centers. The spectra for six, seven, and eight coordinate inorganic and molecular calcium complexes were analyzed and determined to be primarily influenced by the coordination environment and site symmetry at the calcium center. The experimental results are closely correlated to time-dependent density functional theory (TD-DFT) calculations of the XAS spectra. The applicability of this methodology to complex systems was investigated using structural mimics of the oxygen-evolving complex (OEC) of PSII. It was found that Ca K-edge XAS is a sensitive probe for structural changes occurring in the cubane heterometallic cluster due to Mn oxidation. Future applications to the OEC are discussed.

A metastable heterometallic intermediate, [Cu₂(bpy)₂(DIPSA)₂Hg₂(OAc)₄(DIPSA)₂]_n (1, where OAc = CH₃COO^–, bpy = bipyridine, and DIPSA = diisopropylsalicylic acid), has been isolated and characterized during the synthesis of 1D polymer [Cu₂(bpy)₂(DIPSA)₂(CH₃CN)₂Hg₂(OAc)₂(DIPSA)₄]_n (2) at ambient temperature in acetonitrile. Moreover, recrystallization of 2 in methanol results in monomeric [Cu(DIPSA)(bpy)(CH₃OH)]·CH₃OH (3). Complexes 1–3 have been characterized by elemental analysis, Fourier transform infrared, and UV–vis spectroscopy as well as by their single-crystal X-ray structures. The photophysical study suggests the quenching of fluorescence of DIPSA upon complexation.

Tris(abpy) complexes of types mer-[Cu^II(abpy)₃][PF₆]₂ (mer-1²⁺[PF₆^–]₂) and ctc-[Cu^II(abpy)₂(bpy)][PF₆]₂ (ctc-2²⁺[PF₆^–]₂) were successfully isolated and characterized by spectra and single-crystal X-ray structure determinations (abpy = 2,2′-azobispyridine; bpy = 2,2′-bipyridine). Reactions of mer-1²⁺ and ctc-2²⁺ ions with catechol, o-aminophenol, p-phenylenediamine, and diphenylamine (Ph–NH–Ph) in 2:1 molar ratio afford [Cu^I(abpy)₂]⁺ (3⁺) and corresponding quinone derivatives. The similar reactions of [Cu^II(bpy)₃]²⁺ and [Cu^II(phen)₃]²⁺ with these substrates yielding [Cu^I(bpy)₂]⁺ and [Cu^I(phen)₂]⁺ imply that these complexes undergo reduction-induced ligand dissociation reactions (phen = 1,10-phenanthroline). The average −N═N– lengths in mer-1²⁺[PF₆^–]₂ and ctc-2²⁺[PF₆^–]₂ are 1.248(4), while that in 3⁺[PF₆^–]·2CH₂Cl₂ is relatively longer, 1.275(2) Å, due to d_Cu → π_azo* back bonding. In cyclic voltammetry, mer-1²⁺ exhibits one quasi-reversible wave at −0.42 V due to Cu^II/Cu^I and abpy/abpy^•– couples and two reversible waves at −0.90 and −1.28 V due to abpy/abpy^•– couple, while those of ctc-2²⁺ ion appear at −0.44, −0.86, and −1.10 V versus Fc⁺/Fc couple. The anodic 3²⁺/3⁺ and the cathodic 3⁺/3 redox waves at +0.33 and −0.40 V are reversible. The electron paramagnetic resonance spectra and density functional theory (DFT) calculations authenticated the existence of abpy anion radical (abpy^•–) in 3, which is defined as a hybrid state of [Cu^I(abpy^0.5•–)(abpy^0.5•–)] and [Cu^II(abpy^•–)(abpy^•–)] states. 3²⁺ ion is a neutral abpy complex of copper(II) of type [Cu^II(abpy)₂]²⁺. 3 exhibits a near-IR absorption band at 2400–3000 nm because of the intervalence ligand-to-ligand charge transfer, elucidated by time-dependent DFT calculations in CH₂Cl₂.

Because formic acid can be effectively decomposed by catalysis into very pure hydrogen gas, the synthesis of formic acid, especially using CO and H₂O as an intermediate of the water gas shift reaction (WGSR), bears important application significance in industrial hydrogen gas production. Here we report a theoretical study on the mechanism of efficient preparation of formic acid using CO and H₂O catalyzed by a water-soluble [Ru³⁺]-EDTA complex. To determine the feasibility of using the [Ru³⁺]-EDTA catalyst to produce CO-free hydrogen gas in WGSR, two probable reaction paths have been examined: one synthesizes formic acid, while the other converts the reactants directly into CO₂ and H₂, the final products of WGSR. Our calculation results provide a detailed mechanistic rationalization for the experimentally observed selective synthesis of HCOOH by the [Ru³⁺]-EDTA catalyst. The results support the applicability of using the [Ru³⁺]-EDTA catalyst to efficiently synthesize formic acid for hydrogen production. Careful analyses of the electronic structure and interactions of different reaction complexes suggest that the selectivity of the reaction processes is achieved through the proper charge/valence state of the metal center of the [Ru³⁺]-EDTA complex. With the catalytic roles of the ruthenium center and the EDTA ligand being carefully understood, the detailed mechanistic information obtained in this study will help to design more efficient catalysts for the preparation of formic acid and further to produce CO-free H₂ at ambient temperature.

Novel LiCe₉(SiO₄)₆O₂ and LiTb₉(SiO₄)₆O₂ compounds have been successfully synthesized, and the site selectivity and occupancy of activator ions have been estimated including LiEu₉(SiO₄)₆O₂ compound. The rare earth (RE) fully occupied compounds, as well as the RE partially occupied congeners are required for the assessment of site selectivity of RE (activator) ions in apatite-type compounds. The splitting energies of the 6H and 4F Wycoff positions of LiRE₉(SiO₄)₆O₂ (RE = Ce, Eu, and Tb) compounds are calculated based on crystal field theory: ΔE_Ce(6H) = 3849.3 cm^–1, ΔE_Ce(4F) = 4228.1 cm^–1, ΔE_Eu(6H) = 3870.0 cm^–1, ΔE_Eu(4F) = 4092.8 cm^–1, ΔE_Tb(6H) = 3637.6 cm^–1, ΔE_Tb(4F) = 4396.1 cm^–1, indicating that the splitting energy for the 4F site is larger than that for the 6H site in all compounds; thus the absorption energy is higher for the 6H site. In apatite-type LiRE₉(SiO₄)₆O₂ (RE = Ce, Eu, and Tb) compounds, the Ce³⁺ ions predominantly occupy the 4F site associated with the absorption band around 300 nm at lower Ce³⁺ concentration, and then enter the 6H site associated the absorption band around 245 nm. For the Eu³⁺-doped compounds, the 4F site and 6H site are mixed within the charge transfer band (CTB) between 220 and 350 nm. Eu³⁺ ions initially preferentially occupy the 6H site (around 290 nm) at lower Eu³⁺ concentration and subsequently enter the 4F site (around 320 nm) with increasing Eu³⁺ concentration. For the Tb³⁺-doped compounds, the absorption due to the two different sites is mixed within f–d absorption band between 200 and 300 nm. At lower Tb³⁺ concentration, the Tb³⁺ ions enter favorably 6H site around 240 nm and then enter 4F site around 270 nm. These compounds may provide a platform for modeling a new phosphor and application in the solid-state lighting field.

Two isostructural metal–organic framework (MOF) materials, namely, {[MeSi(³Py)₃]₆(Cu₆I₆)}_n (1) and {[ MeSi(³Qy)₃]₆(Cu₆I₆)}_n (2), featuring Cu₆I₆ clusters were synthesized from tridentate arylsilane ligands of the type MeSi(³Py)₃ (³Py = 3-pyridyl) and MeSi(³Qy)₃ (³Qy = 3-quinolyl), respectively. While the MOF 1 displays the usual thermochromism associated with traditional Cu₄I₄Py₄ clusters, the MOF 2 shows ³XLCT/³MLCT emission due to the Cu₆I₆ cluster core at both 298 and 77 K, albeit with some marginal variations in its emission wavelengths. Interestingly, an unusual reversal in the mechanochromic luminescent behavior was observed for these isostructural MOFs at 298 K wherein a pronounced blue-shifted high energy emission for 1 (from orange to yellowish-orange) and a red-shifted low-energy emission for 2 (from green to orange) were obtained upon grinding these samples. This is primarily due to the variations in their cuprophilic interactions as 1 displays shorter Cu···Cu distances (2.745(1) Å) in comparison with those present in 2 (3.148(0) Å). As a result, the ground sample of 2 exhibits a prominent red shift in luminescence owing to the reduction of its Cu···Cu distances to an unknown value closer to the sum of van der Waals radii between two Cu(I) atoms (2.80 Å). However, the blue-shifted emission in 1 is presumably attributed to the rise in its lowest unoccupied molecular orbital energy levels caused by changes in the secondary packing forces. Furthermore, the absorption and emission characteristics of 1 and 2 were substantiated by time-dependent density functional theory calculations on their discrete-model compounds. In addition, the syntheses, reactivity studies, and photophysical properties of two one-dimensional MOFs, namely, {[MeSi(³Qy)₃]₂(Cu₂I₂)}_n (3) and {[MeSi(³Qy)₃](CuI)}_n (4), having dimeric Cu₂I₂ and monomeric CuI moieties, respectively, were examined.

To explore new 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY)-derived metal–organic frameworks (MOFs), we employed 2,6-dicarboxyl-1,3,5,7-tetramethyl-8-phenyl-4,4-difluoroboradiazaindacene (H₂L) as a ligand to successfully synthesize five coordination polymers, namely, {[Zn₂(L)₂(bpp)]·2H₂O·2EtOH}_n (1), {[Cd₂(L)₂(bpp)]·2H₂O·EtOH}_n (2), {[Cd₂(L)(bpe)₃(NO₃)₂]·2H₂O·DMF·EtOH}_n (3), {[Cd(L)(bpe)_0.5(DMF)(H₂O)]}_n (4), and {[Cd(L)(bpe)_0.5]·1.5H₂O·DMF}_n (5) (bpp = 1,3-bi(4-pyridyl)propane, bpe = 1,2-bi(4-pyridyl)ethane). Except for two 2D-layer coordination polymers 3 and 4, the rest samples exhibit 3D metal–organic frameworks with certain pore sizes, especially MOFs 1 and 5. Spectroscopic and crystallographic investigations demonstrate that the absorption and emission energies of the BODIPY chromophores are sensitive to the coordination modes. Moreover, in case 2, the transition metal centers coordinated with the dicarboxylate ligands L^2– are capable of forming the two BODIPY units in coplanar arrangements (θ = 37.9°), simultaneously suppressing the uncommon J-dimer absorption band centered at 705 nm with a long tail into the near-infrared region at room temperature. On the other hand, in comparison with the ligand H₂L, the emission of monomer-like BODIPY in case 3 is enhanced in the solid state by a considerably long distance between the parallel BODIPY planes (about 14.0 Å).

The Fe^III complexes Fe(5-Br-qsal)₂Ni(dmit)₂·solv with solv = CH₂Cl₂ (1) and (CH₃)₂CO (2) were synthesized, and their structural and magnetic properties were studied. While magnetization and Mössbauer spectroscopy data of 1 showed a gradual spin transition, compound 2 evidenced an abrupt transition with a thermal hysteresis of 13 K close to room temperature (T_1/2 ↓ ∼273 K and T_1/2 ↑ ∼286 K). A similar packing arrangement of segregated layers of cations and anions was found for 1 and 2. In both low-spin, LS, structures there are a large number of short intra- and interchain contacts. This number is lower in the high-spin, HS, phases, particularly in the case of 1. The significant loss of strong π–π interactions in the cationic chains and short contacts in the anionic chains in the HS structure of 1 leads to alternating strong and weak bonds between cations along the cationic chains and the formation of unconnected dimers along the anionic chains. This is consistent with a significant weakening of the extended interactions in 1. On the other hand, in the HS phase of 2 the 3D dimensionality of the short contacts observed in the LS phases is preserved. The effect of distinct solvent molecules on the intermolecular spacings explains the different spin crossover behaviors of the title compounds.

NMR crystallography is an emerging method for atomic-resolution structural analysis of ubiquitous vanadium(V) sites in inorganic and bioinorganic complexes as well as vanadium-containing proteins. NMR crystallography allows for characterization of vanadium(V) containing solids, based on the simultaneous measurement of ⁵¹V–¹⁵N internuclear distances and anisotropic spin interactions, described by ¹³C, ¹⁵N, and ⁵¹V chemical shift anisotropy and ⁵¹V electric field gradient tensors. We show that the experimental ⁵¹V, ¹³C, and ¹⁵N NMR parameters are essential for inferring correct coordination numbers and deriving correct geometries in density functional theory (DFT) calculations, particularly in the absence of single-crystal X-ray structures. We first validate this approach on a structurally known vanadium(V) complex, (¹⁵N-salicylideneglycinate)-(benzhydroxamate)oxovanadium(V), VO¹⁵NGlySalbz. We then apply this approach to derive the three-dimensional structure of (methoxo)(¹⁵N-salicylidene-glycinato)oxovanadium(V) with solvated methanol, [VO(¹⁵NGlySal)(OCH₃)]·(CH₃OH). This is a representative complex with potentially variable coordination geometry depending on the solvation level of the solid. The solid material containing molecules of CH₃OH, formally expressed as [VO(¹⁵NGlySal)(OCH₃)]·(CH₃OH), is found to have one molecule of CH₃OH weakly coordinated to the vanadium. The material is therefore best described as [VO(¹⁵NGlySal)(OCH₃)(CH₃OH)] as deduced by the combination of multinuclear solid-state NMR experiments and DFT calculations. The approach reported here can be used for structural analysis of systems that are not amenable to single-crystal X-ray diffraction characterization and which can contain weakly associated solvents.

Density functional theory (in the form of the PW91, BP86, OLYP, and B3LYP exchange–correlation functionals) has been used to map out the low-energy states of a series of eight-coordinate square-antiprismatic (D2d) first-row transition metal complexes, involving Mn(II), Fe(II), Co(II), Ni(II), and Cu(II), along with a pair of tetradentate N4 ligands. Of the five complexes, the Mn(II) and Fe(II) complexes have been synthesized and characterized structurally and spectroscopically, whereas the other three are as yet unknown. Each N4 ligand consists of a pair of terminal imidazole units linked by an o-phenylenediimine unit. The imidazole units are the strongest ligands in these complexes and dictate the spatial disposition of the metal three-dimensional orbitals. Thus, the dx2-y2 orbital, whose lobes point directly at the coordinating imidazole nitrogens, has the highest orbital energy among the five d orbitals, whereas the dxy orbital has the lowest orbital energy. In general, the following orbital ordering (in order of increasing orbital energy) was found to be operative: dxy < dxz = dyz ≤ dz2 < dx2-y2. The square-antiprism geometry does not lead to large energy gaps between the d orbitals, which leads to an S = 2 ground state for the Fe(II) complex. Nevertheless, the dxy orbital has significantly lower energy relative to that of the dxz and dyz orbitals. Accordingly, the ground state of the Fe(II) complex corresponds unambiguously to a dxy2dxz1dyz1dz21dx2-y21 electronic configuration. Unsurprisingly, the Mn(II) complex has an S = 5/2 ground state and no low-energy d-d excited states within 1.0 eV of the ground state. The Co(II) complex, on the other hand, has both a low-lying S = 1/2 state and multiple low-energy S = 3/2 states. Very long metal-nitrogen bonds are predicted for the Ni(II) and Cu(II) complexes; these bonds may be too fragile to survive in solution or in the solid state, and the complexes may therefore not be isolable. Overall, the different exchange–correlation functionals provided a qualitatively consistent and plausible picture of the low-energy d-d excited states of the complexes.

A new family of organometallics of ruthenium(II/III), osmium(II/III/IV), and rhodium(III) ions isolated from C–H activation reactions of dibenzo[1,2]quinoxaline (DBQ) using triphenylphosphine, carbonyl, and halides as coligands is reported. The CN–chelate complexes isolated are trans-[Ru^III(DBQ)(PPh₃)₂Cl₂] (1), trans-[Ru^II(DBQ)(CO)(PPh₃)₂Cl] (2), trans-[Os^III(DBQ)(PPh₃)₂Br₂] (3), trans-[Os^II(DBQ)(PPh₃)₂(CO)Br] (4), and trans-[Rh^III(DBQ)(PPh₃)₂Cl₂] (5). Reaction of 1 with NO affords trans-[Ru(DBQ)(NO)(PPh₃)₂Cl]Cl (6⁺Cl^–), isoelectronic to 2, with a byproduct, [Ru(NO)(PPh₃)₂Cl₃] (7). Complexes 1–5 and 6⁺ were characterized by elemental analyses, mass, IR, NMR, and electron paramagnetic resonance (EPR) spectra including the single-crystal X-ray structure determinations of 1–3 and 5. The Ru^III–C, Ru^II–C, Os^III–C, and Rh^III–C lengths are 2.049(2), 2.074(3), 2.105(16), and 2.012(3) Å in 1, 2, 3, and 5. In cyclic voltammetry, 2, 3, and 4 undergo oxidation at 0.59, 0.39, and 0.46 V, versus Fc⁺/Fc couple, to trans-[Ru^III(DBQ)(CO)(PPh₃)₂Cl]⁺ (2⁺), trans-[Os^IV(DBQ)(PPh₃)₂Br₂]⁺ (3⁺), and trans-[Os^III(DBQ)(CO)(PPh₃)₂Br]⁺ (4⁺) ions. Complex 3⁺ incorporates an Os^IV(d⁴ ion)–C bond. The 6⁺/trans-[Ru(DBQ)(NO)(PPh₃)₂Cl] (6) reduction couple at −0.65 V is reversible. 2⁺, 3⁺, 4⁺ and 6 were substantiated by spectroelectrochemical measurements, EPR spectra, and density functional theory (DFT) and time-dependent (TD) DFT calculations. The frozen-glass EPR spectrum of the electrogenerated 6 exhibits hyperfine couplings due to ^99,101Ru and ¹⁴N nuclei. DFT calculations on trans-[Os^III(DBQ)(PMe₃)₂Br₂] (3^Me), S_t = 1/2 and trans-[Os^IV(DBQ)(PMe₃)₂Br₂]⁺ (3^Me+), S_t = 0, trans-[Ru(DBQ)(NO)(PMe₃)₂Cl]⁺ (6^Me+), S_t = 0 and trans-[Ru(DBQ)(NO)(PMe₃)₂Cl] (6^Me), S_t = 1/2, authenticated a significant mixing between d_Os and π_aromatic* orbitals, which stabilizes M^II/III/IV–C bonds and the [RuNO]⁶ and [RuNO]⁷ states, respectively, in 6⁺ and 6, which is defined as a hybrid state of trans-[Ru^II(DBQ)(NO^•)(PPh₃)₂Cl] and trans-[Ru^I(DBQ)(NO⁺)(PPh₃)₂Cl] states.

Th(IV) readily undergoes hydrolysis and condensation in aqueous solutions to form polynuclear molecular species and the system becomes increasingly complicated when organic chelators or other metals are present in solution, leading to the formation of complexes with vastly different structural topologies. Five compounds containing binary and ternary Th(IV) complexes have been synthesized and structurally characterized using single-crystal X-ray diffraction, including Na₄[Th₆O₂(C₁₀O₇N₂H₁₄)₆]·20.5H₂O (Th₆hedta), [Th(C₉O₆NH₁₂)(H₂O)(NO₃)]·1.5H₂O (Th(ntp)), [Th₂Al₈(OH)₁₄(H₂O)₁₂(C₆O₅NH₈)₄](NO₃)₆·17.5H₂O (Th₂Al₈heidi), (C₄N₂H₁₂) [Th₂Fe₂(OH)₂(H₂O)₂(C₆O₇H₄)₂(C₆O₇H₅)₂]·6H₂O (Th₂Fe₂cit), (C₄N₂H₁₂) [ThFe₂O(H₂O)₃(C₁₁O₉N₂H₁₃)₂]·6H₂O (ThFe₂dhpta). Additional chemical characterization by infrared spectroscopy and thermogravimetric analysis provides information on the chelation by the organic ligands and thermal stability. These molecular complexes can be utilized to understand aqueous speciation in mixed-metal solutions and also provide information regarding contaminant adsorption on iron(III) and aluminum(III) oxide surfaces.

Solvent templates induced Co-based metal–organic materials; conformational isomers {[Co₂(pdpa)(CH₃CN)(H₂O)₃]·CH₃OH·H₂O}_n (1) and {[Co₂(pdpa)(CH₃CN)(H₂O)₃]}_n (2) and {[Co₅(pdpa)₂(μ₃-OH)₂(H₂O)₆]·2H₂O}_n (3) [H₄pdpa = 5,5′-(pentane-1,2-diyl)-bis(oxy)diisophthalic acid] were synthesized under the same solvothermal conditions except with different concentrations of cyclic ethers (1,4-dioxane or tetrahydrofuran) as structure-directing agents. Structural transformations from a three-dimensional (3D) framework of 1 containing channels with dimensions of ∼6 Å × 6 Å to a two-dimensional layer structure of 2 consisting of large open channels with a size of ∼15 Å × 8 Å and then to a 3D nonporous framework of 3, resulting from the different concentrations of cyclic ethers, were observed. The anion−π interactions between electron-efficient oxygen atoms of cyclic ethers and electron-deficient dicarboxylic acid aromatic cores in H₄pdpa imported into the synthetic process accounted for the conformational change of the ligand H₄pdpa and the following structural variations. A systematic investigation was conducted to explore how different concentrations of structure-directing agents affected the frameworks of resultant metal–organic frameworks. Furthermore, 1–3 were shown to be available heterogeneous catalysts for the synthesis of 2-imidazoline and 1,4,5,6-tetrahydropyrimidine derivatives by the cascade cycloaddition reactions of aromatic nitriles with diamines. The results showed that the catalytic activity of 2 was much higher than that of 1 and 3, because of its unique structural features, including accessible catalytic sites and suitable channel size and shape. In addition, a plausible mechanism for these catalytic reactions was proposed, and the reactivity–structure relationship was further clarified.

A new ditopic ligand (L) based on a 2,2′:5′,4″-terpyridine unit substituted in the 2″,6″ positions with iminodiacetate arms has been designed and synthesized for the construction of Ru^IIL₃Ln₃^III supramolecular architectures. The two components of this system, a 2,2′-bipyridine unit for Ru^II coordination and a pyridine-bis(iminodiacetate) core for Ln^III coordination, are tightly connected via a covalent C_arom(py)–C_arom(py) bond. The paramagnetic and photophysical properties of the corresponding tetrametallic Ru^IIL₃Gd₃^III complex have been evaluated, highlighting the potential of this metallostar structure to act as a bimodal MRI/optical imaging agent. Variable-temperature ¹⁷O NMR and proton nuclear magnetic relaxation dispersion (NMRD) measurements showed that this complex exhibits (i) a remarkable relaxivity per metallostar molecule, particularly at clinical and high magnetic fields (r₁^310K = 51.0 and 36.0 mM^–1 s^–1 at 20 and 300 MHz, respectively) and (ii) a near-optimal residence lifetime of Gd^III coordinated water molecule (τ_M^310K = 77.5 ns). This is the result of the presence of two inner-sphere water molecules in the Gd^III components of the metallostar and a slow tumbling rate of the molecule (τ_R^310K = 252 ps). Upon excitation in the visible domain (λ_exc = 472 nm), the Ru^II component of the complex exhibits a bright-red luminescence centered at 660 nm with a quantum yield of 2.6% in aqueous solutions at pH 7.4. Moreover, this Ru^IIL₃Gd₃^III assembly is also characterized by a high kinetic inertness in biological media (PBS and human serum solutions) and a high photostability (photobleaching). Finally, preliminary photophysical studies on RuL₃Nd₃ and RuL₃Yb₃ assemblies revealed that the Ru^II center acts as an effective sensitizer for Ln^III-based luminescence in the near-IR region. The Nd^III species was found to be the most effective at quenching the ³MLCT luminescence of the Ru center.

Ligands containing the [2,6-bis(1,2,3-triazol-4-yl)pyridine] (btp) motif have recently shown promise in coordination chemistry. The motif is synthesized via the Cu(I)-catalyzed “click” reaction and can be conveniently functionalized when compared to other terdentate chelating motifs. Ligand 1 was synthesized and shown to sensitize Eu(III) and Tb(III) excited states effectively. The use of these ions to synthesize self-assembly structures in solution was investigated by carrying out both ¹H NMR and photophysical titrations. The latter were used to determine high binding constants from changes in the absorption, ligand emission (fluorescence), and lanthanide-centered emission. A small library of amino acid derivatives of 1, ligands 3, were prepared upon coupling reactions with Gly, Ala, Phe, and Trp methyl esters, with a view to introducing biologically relevant and chiral moieties into such ligands. All of these derivatives were shown to form stable, emissive Ln(III) self-assemblies, emitting in the millisecond time range, which were studied by means of probing their photophysical properties in organic solutions using lanthanide ion titrations. All the Tb(III) complexes, with the exception of Trp based derivatives, gave rise to highly luminescent and bright complexes, with quantum yields of Tb(III) emission of 46–70% in CH₃CN solution. In contrast, the Eu(III) complexes gave rise to more modest quantum yields of 0.3–3%, reflecting better energy match for the Tb(III) complexes, and hence, more efficient sensitization, as demonstrated by using low temperature measurements to determine the triplet state of 1.

Naturally occurring hydroxyapatite, Ca₅(PO₄)₃(OH) (HAP), is the main inorganic component of bone matrix, with synthetic analogues finding applications in bioceramics and catalysis. An interesting and valuable property of both natural and synthetic HAP is the ability to undergo cationic and anionic substitution. The lanthanides are well-suited for substitution for the Ca²⁺ sites within HAP, because of their similarities in ionic radii, donor atom requirements, and coordination geometries. We have used isothermal titration calorimetry (ITC) to investigate the thermodynamics of ion exchange in HAP with a representative series of lanthanide ions, La³⁺, Sm³⁺, Gd³⁺, Ho³⁺, Yb³⁺ and Lu³⁺, reporting the association constant (K_a), ion-exchange thermodynamic parameters (ΔH, ΔS, ΔG), and binding stoichiometry (n). We also probe the nature of the La³⁺:HAP interaction by solid-state nuclear magnetic resonance (³¹P NMR), X-ray diffraction (XRD), and inductively coupled plasma–optical emission spectroscopy (ICP-OES), in support of the ITC results.

Electrogenerated chemiluminescence (ECL) with different emission colors is important in the development of multichannel analytical techniques. In this report, five new heteroleptic iridium(III) complexes were synthesized, and their photophysical, electrochemical, and ECL properties were studied. Here, 2-(2,4-difluorophenyl)pyridine (dfppy, complex 1), 2-phenylbenzo[d]thiazole (bt, complex 2), and 2-phenylpyridine (ppy, complex 3) were used as the main ligands to tune the emission color, while avobenzone (avo) was used as the ancillary ligand. For comparison, complexes 4 and 5 with 2-phenylpyridine and 2-phenylbenzo[d]thiazole as the main ligand, respectively, and acetyl acetone (acac) as the ancillary ligand were also synthesized. All five iridium(III) complexes had strong intraligand absorption bands (π–π*) in the UV region (below 350 nm) and a featureless MLCT (d−π*) transition in the visible 400–500 nm range. Multicolored emissions were observed for these five iridium(III) complexes, including green, orange, and red for complexes 4, 5, 2, 1, 3, respectively. Density functional theory calculations indicate that the electronic density of the highest occupied molecular orbital is entirely located on the C^N ligands and the iridium atom, while the formation of the lowest unoccupied molecular orbital (LUMO) is complicated. The LUMO is mainly assigned to the ancillary ligand for complexes 1 and 3 but to the C^N ligand for complexes 2, 4, and 5. Cyclic voltammetry studies showed that all these complexes have a reversible oxidation wave, but no reduction waves were found in the electrochemical windows of CH₂Cl₂. The E_1/2^ox values of these complexes ranged from 0.642 to 0.978 V for complexes 3, 4, 2, 5, 1, (in increasing order) and are all lower than that of Ru(bpy)₃²⁺. Most importantly, when using tripropylamine as a coreactant, complexes 1–5 exhibited intense ECL signals with an emission wavelength centered at 616, 580, 663, 536, and 569 nm, respectively. In addition, complexes 1, 2, and 5 displayed approximately 2, 11, and 214 times higher ECL efficiencies than Ru(bpy)₃²⁺ under identical conditions.

Four alkoxohexavanadate-based Pd-POVs [Pd(dpa)(acac)]₂[V₆O₁₃(OMe)₆] (1), [Pd(dpa)(acac)]₂[V₆O₁₁(OMe)₈] (2), [Pd(dpa)(acac)]₂[V₆O₁₁(OMe)₈]·H₂O (3), and [Pd(DMAP)₂(acac)]₂[V₆O₁₁(OMe)₈]·H₂O (4) (POV = polyoxovanadate; dpa = 2,2′-dipyridine amine; DMAP = 4-dimethylaminopyridine; acac = acetylacetone anion) have been synthesized and fully characterized by single crystal X-ray diffraction and powder X-ray diffraction analyses, Fourier transform infrared spectroscopy, element analyses, and X-ray photoelectron spectroscopy. In 1–4, Pd complexes and hexavanadate anions are assembled through electrostatic interactions. Interestingly, the [V₆O₁₁(OMe)₈]^2– cores in 2 and 3 are a pair of isomers that can be isolated by controlling crystallization temperature. Moreover, to the best of our knowledge, the {V6} core in 3 represents a new octamethoxyhexavanadates cluster. It is notable that compounds 1–4 exhibit excellent heterogeneous catalytic performance in the oxidation of benzyl-alkanes with t-butylhydroperoxide as oxidant. Among them, the catalytic activity of 1 (conv. and selec. up to 99%, respectively) outperforms others and can be reused without losing its activity.

So far, more than 1000 UV converted phosphors have been reported for potential application in white light-emitting diodes (WLEDs), but most of them (e.g., Y₂O₂S:Eu, YAG:Ce or CaAlSiN₃:Eu) suffer from intrinsic problems such as thermal instability, color aging or re-absorption by commixed phosphors in the coating of the devices. In this case, it becomes significant to search a single-phased phosphor, which can efficiently convert UV light to white lights. Herein, we report a promising candidate of a white light emitting X2-type Y₂SiO₅:Eu³⁺,Bi³⁺ phosphor, which can be excitable by UV light and address the problems mentioned above. Single Bi³⁺-doped X2-type Y₂SiO₅ exhibits three discernible emission peaks at ∼355, ∼408, and ∼504 nm, respectively, upon UV excitation due to three types of bismuth emission centers, and their relative intensity depends tightly on the incident excitation wavelength. In this regard, proper selection of excitation wavelength can lead to tunable emissions of Y₂SiO₅:Bi³⁺ between blue and green, which is partially due to the energy transfer among the Bi centers. As a red emission center Eu³⁺ is codoped into Y₂SiO₅:Bi³⁺, energy transfer has been confirmed happening from Bi³⁺ to Eu³⁺ via an electric dipole–dipole (d–d) interaction. Our experiments reveal that it is easily realizable to create the white or tunable emissions by adjusting the Eu³⁺ content and the excitation schemes. Moreover, a single-phased white light emission phosphor, X2-type Y_1.998SiO₅:0.01Eu³⁺,0.01 Bi³⁺, has been achieved with excellent resistance against thermal quenching and a QE of 78%. At 200 °C, it preserves >90% emission intensity of that at 25 °C. Consequent three time yoyo experiments of heating–cooling prove no occurrence of thermal degradation. A WLED lamp has been successfully fabricated with a CIE chromaticity coordinate (0.3702, 0.2933), color temperature 4756 K, and color rendering index of 65 by applying the phosphor onto a UV LED chip.

Synthesis, characterization, electrochemical studies, and ATRP activity of a series of novel copper(I and II) complexes with TPMA-based ligands containing 4-methoxy-3,5-dimethyl-substituted pyridine arms were reported. In the solid state, Cu^I(TPMA*¹)Br, Cu^I(TPMA*²)Br, and Cu^I(TPMA*³)Br complexes were found to be distorted tetrahedral in geometry and contained coordinated bromide anions. Pseudo-coordination of the aliphatic nitrogen atom to the copper(I) center was observed in Cu^I(TPMA*²)Br and Cu^I(TPMA*³)Br complexes, whereas pyridine arm dissociation occurred in Cu^I(TPMA*¹)Br. All copper(I) complexes with substituted TPMA ligands exhibited a high degree of fluxionality in solution. At low temperature, Cu^I(TPMA*¹)Br was found to be symmetrical and monomeric, while dissociation of either unsubstituted pyridine and/or 4-methoxy-3,5-dimethyl-substituted pyridine arms was observed in Cu^I(TPMA*²)Br and Cu^I(TPMA*³)Br. On the other hand, the geometry of the copper(II) complexes in the solid state deviated from ideal trigonal bipyramidal, as confirmed by a decrease in τ values ([Cu^II(TPMA*¹)Br][Br] (τ = 0.92) > [Cu^II(TPMA*³)Br][Br] (τ = 0.77) > [Cu^II(TPMA*²)Br][Br] (τ = 0.72)). Furthermore, cyclic voltammetry studies indicated a nearly stepwise decrease (ΔE ≈ 60 mV) of E_1/2 values relative to SCE (TPMA (−240 mV) > TPMA*¹ (−310 mV) > TPMA*² (−360 mV) > TPMA*³ (−420 mV)) on going from [Cu^II(TPMA)Br][Br] to [Cu^II(TPMA*³)Br][Br], confirming that the presence of electron-donating groups in the 4 (−OMe) and 3,5 (−Me) positions of the pyridine rings in TPMA increases the reducing ability of the corresponding copper(I) complexes. This increase was mostly the result of a stronger influence of substituted TPMA ligands toward stabilization of the copper(II) oxidation state (log β^I = 13.4 ± 0.2, log β^II = 19.3 (TPMA*¹), 20.5 (TPMA*²), and 21.5 (TPMA*³)). Lastly, ARGET ATRP kinetic studies show that with more reducing catalysts an induction period is observed. This was attributed to slow regeneration of Cu^I species from the corresponding Cu^II.

The reactions of Cu(ClO₄)₂ with NaCN and the ditopic ligands m-bis[bis(1-pyrazolyl)methyl]benzene (L_m) or m-bis[bis(3,5-dimethyl-1-pyrazolyl)methyl]benzene (L_m*) yield [Cu₂(μ-CN)(μ-L_m)₂](ClO₄)₃ (1) and [Cu₂(μ-CN)(μ-L_m*)₂](ClO₄)₃ (3). In both, the cyanide ligand is linearly bridged (μ-1,2) leading to a separation of the two copper(II) ions of ca. 5 Å. The geometry around copper(II) in these complexes is distorted trigonal bipyramidal with the cyanide group in an equatorial position. The reaction of [Cu₂(μ-F)(μ-L_m)₂](ClO₄)₃ and (CH₃)₃SiN₃ yields [Cu₂(μ-N₃)(μ-L_m)₂](ClO₄)₃ (2), where the azide adopts end-on (μ-1,1) coordination with a Cu–N–Cu angle of 138.0° and a distorted square pyramidal geometry about the copper(II) ions. Similar chemistry in the more sterically hindered L_m* system yielded only the coordination polymer [Cu₂(μ-L_m*)(μ-N₃)₂(N₃)₂]. Attempts to prepare a dinuclear complex with a bridging iodide yield the copper(I) complex [Cu₅(μ-I₄)(μ-L_m*)₂]I₃. The complexes 1 and 3 show strong antiferromagnetic coupling, −J = 135 and 161 cm^–1, respectively. Electron paramagnetic resonance (EPR) studies coupled with density functional theory (DFT) calculations show that the exchange interaction is transmitted through the d_z² and the bridging ligand s and p_x orbitals. High field EPR studies confirmed the d_z² ground state of the copper(II) ions. Single-crystal high-field EPR has been able to definitively show that the signs of D and E are positive. The zero-field splitting is dominated by the anisotropic exchange interactions. Complex 2 has −J = 223 cm^–1 and DFT calculations indicate a predominantly d_x²–y² ground state.

We have prepared the oxyhydride perovskite EuTiO_3–xH_x (x ≤ 0.3) by a low temperature CaH₂ reduction of pyrochlore Eu₂Ti₂O₇ and perovskite EuTiO₃. The reduced EuTiO_3–xH_x crystallizes in the ideal cubic perovskite (Pm3̅m), where O/H anions are randomly distributed. As a result of electron doping by the aliovalent anion exchange, the resistivity of EuTiO_3–xH_x shows metallic temperature dependence. Moreover, an antiferromagnetic-to-ferromagnetic transition is observed even when a small amount of hydride (x ∼ 0.07) is introduced. The Curie temperature T_C of 12 K is higher than those of any other EuTiO₃-derived ferromagnets. The ferromagnetism can be explained by the Ruderman–Kittel–Kasuya–Yosida (RKKY) interaction between the Eu²⁺ spins mediated by the itinerant Ti 3d electrons. The present study shows that controlling the oxide/hydride ratio is a versatile method to tune magnetic and transport properties.

The synthetic chemistry of substituted 4,4′-azobis(phenylcyanamide) ligands was investigated, and the complexes [{Ru(tpy)(bpy)}₂(μ-L)][PF₆]₂, where L = 2,2′:5,5′-tetramethyl-4,4′-azobis(phenylcyanamido) (Me₄adpc^2–), 2,2′-dimethyl-4,4′-azobis(phenylcyanamido) (Me₂adpc^2–), unsubstituted (adpc^2–), 3,3′-dichloro-4,4′-azobis(phenylcyanamido) (Cl₂adpc^2–), and 2,2′:5,5′-tetrachloro-4,4′-azobis(phenylcyanamido) (Cl₄adpc^2–), were prepared and characterized by cyclic voltammetry and vis–near-IR (NIR) and IR spectroelectrochemistry. The room temperature electron paramagnetic resonance spectrum of [{Ru(tpy)(bpy)}₂(μ-Me₄adpc)]³⁺ showed an organic radical signal and is consistent with an oxidation-state description [Ru^II, Me₄adpc^•–, Ru^II]³⁺, while that of [{Ru(tpy)(bpy)}₂(μ-Cl₂adpc)]³⁺ at 10 K showed a low-symmetry Ru^III signal, which is consistent with the description [Ru^III, Cl₂adpc^2–, Ru^II]³⁺. IR spectroelectrochemistry data suggest that [{Ru(tpy)(bpy)}₂(μ-adpc)]³⁺ is delocalized and [{Ru(tpy)(bpy)}₂(μ-Cl₂adpc)]³⁺ and [{Ru(tpy)(bpy)}₂(μ-Cl₄adpc)]³⁺ are valence-trapped mixed-valence systems. A NIR absorption band that is unique to all [{Ru(tpy)(bpy)}₂(μ-L)]³⁺ complexes is observed; however, its energy and intensity vary depending on the nature of the bridging ligand and, hence, the complexes’ oxidation-state description.

In a series of two-dimensional layered frameworks constructed by two electron-donor (D) and one electron-acceptor (A) units (a D₂A framework), two-electron transferred systems with D⁺₂A^2– were first synthesized as [{Ru₂(R-PhCO₂)₄}₂(TCNQR_x)]·n(solv) (R = o-CF₃, R_x = H₂ (1), R = o-CF₃, R_x = Me₂ (2), R = o-CF₃, R_x = F₄ (3), R = o-Me, TCNQR_x = BTDA-TCNQ (4), R = p-Me, TCNQR_x = BTDA-TCNQ (5), where TCNQ is 7,7,8,8-tetracyano-p-quinodimethane and BTDA-TCNQ is bis[1,2,5]dithiazolotetracyanoquinodimethane). The D⁺₂A^2– system was synthesized by assembling D/A combinations of paddlewheel-type [Ru₂^II,II(R-PhCO₂)₄] complexes and TCNQR_x that possibly caused a large gap between the HOMO of D and the LUMO of A (ΔE_H–L(DA)). All compounds were paramagnetic because of quasi-isolated [Ru₂^II,III]⁺ units with weakly antiferromagnetically coupled S = 3/2 spins via diamagnetic TCNQR_x^2– and/or through the interlayer space. The ionic states of these compounds were determined using the HOMO/LUMO energies and redox potentials of the D and A components in the ionization diagram for ΔE_H–L(DA) vs ΔE_1/2(DA) (= E_1/2(D) – E_1/2(A); E_1/2 = first redox potential) as well as by previously reported data for the D₂A and DA series of [Ru₂]/TCNQ, DCNQI materials. The boundary between the one-electron and the two-electron transferred ionic regimes (1e–I and 2e–I, respectively) was not characterized. Therefore, another diagram for ΔE_H–L(DA) vs |²E_1/2(A) – ¹E_1/2(A)|, where ²E_1/2(A) and ¹E_1/2(A) are the second and first redox potentials of TCNQR_x, respectively, was used because the 2e–I regime is dependent on on-site Coulomb repulsion (U = |²E_1/2(A) – ¹E_1/2(A)|) of TCNQR_x. This explained the oxidation states of 1–5 and the relationship between ΔE_H–L(DA) and U and allowed us to determine whether the ionic regime was 1e–I or 2e–I. These diagrams confirm that a charge-oriented choice of building units is possible even when designing covalently bonded D₂A framework systems.

While a number of chelate strategies have been developed for the organometallic precursor fac-[M^I(OH₂)₃(CO)₃]⁺ (M = Re, ^99mTc), a unique challenge has been to improve the overall function and performance of these complexes for in vivo and in vitro applications. Since its discovery, fac-[M^I(OH₂)₃(CO)₃]⁺ has served as an essential scaffold for the development of new targeted ^99mTc based radiopharmaceuticals due to its labile aquo ligands. However, the lipophilic nature of the fac-[M^I(CO)₃]⁺ core can influence the in vivo pharmacokinetics and biodistribution of the complexes. In an effort to understand and improve this behavior, monosubstituted pyridine ligands were used to assess the impact of donor nitrogen basicity on binding strength and stability of fac-[M^I(CO)₃]⁺ in a 2 + 1 labeling strategy. A series of Re and ^99mTc complexes were synthesized with picolinic acid as a bidentate ligand and 4-substituted pyridine ligands. These complexes were designed to probe the effect of pK_a from the monodentate pyridine ligand both at the macro scale and radiochemical concentrations. Comparison of X-ray structural data and radiochemical solution experiments clearly indicate an increase in overall yield and stability as pyridine basicity increased.

The presence of an Fe^V(O) species has been postulated as the active intermediate for the oxidation of both C–H and C═C bonds in the Rieske dioxygenase family of enzymes. Understanding the reactivity of these high valent iron–oxo intermediates, especially in an aqueous medium, would provide a better understanding of these enzymatic reaction mechanisms. The formation of an Fe^V(O) complex at room temperature in an aqueous CH₃CN mixture that contains up to 90% water using NaOCl as the oxidant is reported here. The stability of Fe^V(O) decreases with increasing water concentration. We show that the reactivity of Fe^V(O) toward the oxidation of C–H bonds, such as those in toluene, can be tuned by varying the amount of water in the H₂O/CH₃CN mixture. Rate acceleration of up to 60 times is observed for the oxidation of toluene upon increasing the water concentration. The role of water in accelerating the rate of the reaction has been studied using kinetic measurements, isotope labeling experiments, and density functional theory (DFT) calculations. A kinetic isotope effect of ∼13 was observed for the oxidation of toluene and d₈-toluene showing that C–H abstraction was involved in the rate-determining step. Activation parameters determined for toluene oxidation in H₂O/CH₃CN mixtures on the basis of Eyring plots for the rate constants show a gain in enthalpy with a concomitant loss in entropy. This points to the formation of a more-ordered transition state involving water molecules. To further understand the role of water, we performed a careful DFT study, concentrating mostly on the rate-determining hydrogen abstraction step. The DFT-optimized structure of the starting Fe^V(O) and the transition state indicates that the rate enhancement is due to the transition state’s favored stabilization over the reactant due to enhanced hydrogen bonding with water.

Four spinel ferrite compositions of the CuAl_xFe_2–xO₄, x = 0.0, 0.2, 0.4, 0.6, system prepared by usual double-sintering ceramic route and quenched (rapid thermal cooling) from final sintering temperature (1373 K) to liquid nitrogen temperature (80 K) were investigated by employing X-ray powder diffractometry, ⁵⁷Fe Mossbauer spectroscopy, and micro-Raman spectroscopy at 300 K. The Raman spectra collected in the wavenumber range of 100–1000 cm^–1 were analyzed in a systematic manner and showed five predicted modes for the spinel structure and splitting of A_1g Raman mode into two/three energy values, attributed to peaks belonging to each ion (Cu²⁺, Fe³⁺, and Al³⁺) in the tetrahedral positions. The suppression of lower-frequency peaks was explained on the basis of weakening in magnetic coupling and reduction in ferrimagnetic behavior as well as increase in stress induced by square bond formation on Al³⁺ substitution. The enhancement in intensity, random variation of line width, and blue shift for highest frequency peak corresponding to A_1g mode were observed. The ferric ion (Fe³⁺) concentration for different compositions determined from Raman spectral analysis agrees well with that deduced by means of X-ray diffraction line-intensity calculations and Mossbauer spectral analysis. An attempt was made to determine elastic and thermodynamic properties from Raman spectral analysis and elastic constants from cation distribution.

Pure BaMgSiO₄:Eu²⁺ phosphor, prepared by a solid state reaction method under N₂ atmosphere, exhibited a strong green emission at 500 nm and a weak emission at 405 nm. Heat treatment under NH₃ atmosphere causes changes in the PL intensity: the green emission at 500 nm gradually decreases and completely disappears after heat treatment for 3 h, whereas a new blue emission peak, centered at 445 nm, appears and becomes very strong. The results of the analyses with electron paramagnetic resonance (EPR), X-ray photoelectron spectroscopy (XPS), and X-ray absorption fine structure (XAFS) spectroscopy suggest that the heat treatment causes the generation of a large amount of oxygen vacancies. This resulted in the aforementioned color changes of the BaMgSiO₄:Eu phosphor, which are confirmed by the results of DFT+U calculations. In particular, these calculations showed that Eu prefers to occupy Ba(3) sites, which are six coordinated to oxygen atoms. The emission at 500 nm was attributed to the 4f–5d transition energy of Eu in Ba(3) site, calculated as 2.54 eV. It was also shown that Eu 4f energy level decreases when oxygen is removed from the oxygen position adjacent to Eu, which results in a larger Eu 4f–5d transition energy and shorter wavelengths of emission peaks.

The quaternary transition metal oxyselenide Ce₂O₂ZnSe₂ has been shown to adopt a ZrCuSiAs-related structure with Zn²⁺ cations in a new ordered arrangement within [ZnSe₂]^2– layers. The color of the compound changes as a function of cell volume, which can vary by ∼0.4% under different synthetic conditions. At the highest, intermediate, and lowest cell volumes, the color is yellow-ochre, brown, and black, respectively. The decreased volume is attributed to oxidation of Ce from 3+ to 4+, the extent of which can be controlled by synthetic conditions. Ce₂O₂ZnSe₂ is a semiconductor at all cell volumes with experimental optical band gaps of 2.2, 1.4, and 1.3 eV for high, intermediate, and low cell volume samples, respectively. SQUID measurements show Ce₂O₂ZnSe₂ to be paramagnetic from 2 to 300 K with a negative Weiss temperature of θ = −10 K, suggesting weak antiferromagnetic interactions.

Two inverse 2-pyridyl-1,2,3-triazole “click” ligands, 2-(4-phenyl-1H-1,2,3-triazol-1-yl)pyridine and 2-(4-benzyl-1H-1,2,3-triazol-1-yl)pyridine, and their palladium(II), platinum(II), rhenium(I), and ruthenium(II) complexes have been synthesized in good to excellent yields. The properties of these inverse “click” complexes have been compared to the isomeric regular compounds using a variety of techniques. X-ray crystallographic analysis shows that the regular and inverse complexes are structurally very similar. However, the chemical and physical properties of the isomers are quite different. Ligand exchange studies and density functional theory (DFT) calculations indicate that metal complexes of the regular 2-(1-R-1H-1,2,3-triazol-4-yl)pyridine (R = phenyl, benzyl) ligands are more stable than those formed with the inverse 2-(4-R-1H-1,2,3-triazol-1-yl)pyridine (R = phenyl, benzyl) “click” chelators. Additionally, the bis-2,2′-bipyridine (bpy) ruthenium(II) complexes of the “click” chelators have been shown to have short excited state lifetimes, which in the inverse triazole case, resulted in ejection of the 2-pyridyl-1,2,3-triazole ligand from the complex. Under identical conditions, the isomeric regular 2-pyridyl-1,2,3-triazole ruthenium(II) bpy complexes are photochemically inert. The absorption spectra of the inverse rhenium(I) and platinum(II) complexes are red-shifted compared to the regular compounds. It is shown that conjugation between the substituent group R and triazolyl unit has a negligible effect on the photophysical properties of the complexes. The inverse rhenium(I) complexes have large Stokes shifts, long metal-to-ligand charge transfer (MLCT) excited state lifetimes, and respectable quantum yields which are relatively solvent insensitive.

The emission properties of a series of cationic Pt(II) complexes bearing neutral tridentate 2,6-bis-(1H-1,2,3-triazol-5-yl)pyridine and monoanionic ancillary ligands (Cl^– or CN^–) are described. By varying the substitution pattern on the 1,2,3-triazole moieties of the tridentate luminophore and the nature of the ancillary ligand, we were able to tune the intermolecular interactions between the complexes and therefore the electronic interactions between the metal centers. Indeed, all the compounds possessing Cl^– as ancillary ligand are nonluminescent at room temperature, while the complexes containing CN^– are luminescent. Interestingly, the π-accepting nature of this ancillary ligand induces Pt(II)–Pt(II) interactions irrespectively of bulky substitution patterns on the tridentate ligand.

Two compounds of formula {(H₃O)[Cu₇(Hmesox)₅(H₂O)₇]·9H₂O}_n (1a) and {(NH₄)_0.6(H₃O)_0.4[Cu₇(Hmesox)₅(H₂O)₇]·11H₂O}_n (1b) were prepared and structurally characterized by single-crystal X-ray diffraction (H₄mesox = mesoxalic acid, 2-dihydroxymalonic acid). The compounds are crystalline functional metal–organic frameworks exhibiting proton conduction and magnetic ordering. Variable-temperature magnetic susceptibility measurements reveal that the copper(II) ions are strongly ferro- and antiferromagnetically coupled by the alkoxide and carboxylate bridges of the mesoxalate linker to yield long-range magnetic ordering with a T_c of 17.6 K, which is reached by a rare mechanism known as topologic ferrimagnetism. Electric conductivity, measured by impedance methods, shows values as high as 6.5 × 10^–5 S cm^–1 and occurs by proton exchange among the hydronium/ammonium and water molecules of crystallization, which fill the voids left by the three-dimensional copper(II) mesoxalate anionic network.

Mercury(II) anions derived from the F₅TeO– (teflate) group were synthesized and structurally characterized. The salts, [N(CH₂CH₃)₄]₂[Hg(OTeF₅)₄], [N(CH₃)₄]₃[Hg(OTeF₅)₅], [N(CH₂CH₃)₄]₃[Hg(OTeF₅)₅], [N(CH₃)₄]₂[Hg₂(OTeF₅)₆], Cs₂[Hg(OTeF₅)₄]·Hg(OTeF₅)₂, and {Cs₃[Hg₂(OTeF₅)₇]·Hg(OTeF₅)₂}·4SO₂ClF, were obtained by reaction of Hg(OTeF₅)₂ with [M][OTeF₅] (M = [N(CH₃)₄]⁺, [N(CH₂CH₃)₄]⁺, Cs⁺) and were characterized by low-temperature single-crystal X-ray diffraction and low-temperature Raman spectroscopy. Unlike in the extensively fluorine-bridged solid-state structures of [HgF₃]⁻ and [HgF₄]^2–, the less basic and more sterically demanding teflate ligands of the Hg(II) anions show less tendency to bridge. The anions exhibit a variety of structural motifs, ranging from well-isolated tetrahedral [Hg(OTeF₅)₄]^2– and square-pyramidal [Hg(OTeF₅)₅]^3– to the chain structures, [Hg₂(OTeF₅)₆]^2– and [Hg₂(OTeF₅)₇]^3–·Hg(OTeF₅)₂. The geometrical parameters and vibrational frequencies of [Hg(OTeF₅)₄]^2– (S₄), [Hg(OTeF₅)₅]^3– (C₁), and [Hg₂(OTeF₅)₆]^2– (D₂) anions, as well as the hypothetical [Hg₃(OTeF₅)₈]^2– (C₁) anion, were calculated using density functional theory methods (PBE1PBE/def2-TZVPP), which aided in the assignment of the Raman spectra of [Hg(OTeF₅)₄]^2–, [Hg(OTeF₅)₅]^3–, [Hg₂(OTeF₅)₆]^2–, and Cs₂[Hg(OTeF₅)₄]·Hg(OTeF₅)₂. The calculated geometries were used to assess the effects of solid-state interionic interactions on the anion geometries. For the most part, the gross gas-phase trigonal bipyramidal (tbp) geometry of [Hg(OTeF₅)₅]^3– adheres to the predicted VSEPR geometry but contrasts with the solid-state anion structures, which have square-pyramidal geometries or geometries that lie between square pyramidal- and tbp-geometries. However, the bond length order calculated for the Hg–O bonds of tbp-[Hg(OTeF₅)₅]^3–, Hg–O_eq > Hg–O_ax, is opposite to that predicted by the VSEPR model of molecular geometry. Natural bond orbital analyses provided the associated Mayer bond orders, Mayer valencies, and natural population analysis charges.

Here we demonstrate a novel and facile strategy of highly luminescent water-soluble Zn-doped AgIn₅S₈ (ZAIS) nanocrystals and ZAIS/ZnS core/shell structures, which were based on hydrothermal reaction between the acetate salts of the corresponding metals and sulfide precursor in the presence of l-cysteine at 110 °C in a Teflon-lined autoclave. The photoluminescent (PL) emission wavelength can be conveniently tuned from 560 to 650 nm by tailoring the stoichiometric ratio of [Ag]/[Zn]. The as prepared nanocrystals were characterized systematically and exhibit long PL lifetimes more than 100 ns. The influence of experimental conditions, including concentration of l-cysteine and reaction temperature, was investigated. In addition, we performed a coating procedure with the ZnS shell outside the ZAIS core and showed excellent PL quantum yields up to 35%. The in vitro experiment exhibited quite low cytotoxicity and marvelous biocompatibility, revealing their promising prospect in bioscience. Furthermore, the obtained ZAIS/ZnS nanocompounds (NCs) were covalently conjugated to alpha-fetoprotein antibodies and targeted fluorescent imaging for hepatocellular carcinoma cells was realized.

The coordination properties of isopropylxanthate (i-Pr-Tiox) and pyridine-2-thiolate (PyS) toward the [M(PS)₂]⁺ moiety (M = Re and ^99mTc; PS = phosphinothiolate) were investigated. Synthesis and full characterization of [Re(PS2)₂(i-Pr-Tiox)] (Re1), [Re(PSiso)₂(i-Pr-Tiox)] (Re2), [Re(PS2)₂(PyS)] (Re3), and [Re(PSiso)₂(PyS)] (Re4), where PS2 = 2-(diphenylphosphino)ethanethiolate and PSiso = 2-(diisopropylphosphino)ethanethiolate, and the structural X-ray analysis of complex Re3 were carried out. ^99mTc analogues of complexes Re2 (^99mTc2) and Re4 (^99mTc4) were obtained in high radiochemical yield following a simple one-pot procedure. The chemical identity of the radiolabeled compounds was confirmed by chromatographic comparison with the corresponding rhenium complexes and by dual radio/UV HPLC analysis combined with ESI(+)-MS of ^99g/99mTc complexes prepared in carrier-added conditions. The two radiolabeled complexes were stable with regard to trans chelation with cysteine, glutathione, and ethylenediaminotetraacetic acid and in rat and human sera. This study highlights the substitution-inert metal-fragment behavior of the [M(PS)₂]⁺ framework, which reacts with suitable bidentate coligands to form stable hexacoordinated asymmetrical complexes. This feature makes it a promising platform on which to develop a new class of Re/Tc complexes that are potentially useful in radiopharmaceutical applications.

We propose and validate a simple strategy of vertex connection that can be used for framework design and pore size/type modulation to prepare a mother structure and another 10 highly porous isoreticular frameworks with unprecedented topology. Importantly, the potential accessible pore volumes (57–71%), pore sizes (6.8–11. 2 Å; 17.0–29.0 Å; 12.5–22.8 Å; 11.9–24.5 Å), and the pore shapes of this series of highly porous frameworks were simultaneously and systematically tuned. Interestingly, the pore size of IIa [Zn₄O(L²)₂(BDC)_0.5]{(CH₃)₂NH₂} decreased a little less than that of IIc [Zn₄O(L²)₂(2,6-NDC)_0.5]{(CH₃)₂NH₂}; however, its selectivity of CO₂ toward CH₄ increased by almost two times.

We demonstrate that an asymmetric composite cluster, [Ag₂₅{C≡CC(CH₃)₃}₁₆(CH₃CN)₄(P₂W₁₅Nb₃O₆₂)] (1), consisting of directly fused polyoxometalate and silver alkynide moieties can be facilely synthesized by a one-pot reaction between a Nb-substituted Dawson-type polyoxometalate, H₄[α-P₂W₁₅Nb₃O₆₂]^5–, and the mixture of (CH₃)₃CC≡CAg and CF₃SO₃Ag. Single-crystal X-ray diffraction revealed the structure of 1, where Ag atoms are selectively attached to the Nb-substituted hemisphere of the pedestal Dawson anion. Its structural integrity in the solution was demonstrated by ³¹P NMR spectroscopy and analytical ultracentrifugation. The latter method also unveiled the stepwise formation mechanism of 1.

In search of porous materials for selective sorption and iodine inclusion, we have found two networks made of chains with a kink at the metal nodes held together by supramolecular interactions (H-bond and π···π stacking). The solvent can be removed and replaced reversibly without loss of crystallinity, as demonstrated by single-crystal-to-single-crystal crystallography. In contrast, iodine uptake degrades the crystallinity to amorphous, and it regains its crystalline state after removal of the iodine at 200 °C. Slight differences in behavior of the sorption and inclusion properties between the tetrahedral metal nodes, Zn and Co, are associated with the size of the nodes. An important feature is the extent of iodine that can be included between the chains that is doubled with temperature from 30 to 100 °C and exceeds the weight in mass of the compounds.

Density functional theory (DFT) studies on two polynuclear clusters, [Cu^II₅Gd^III₄O₂(OMe)₄(teaH)₄(O₂CC(CH₃)₃)₂(NO₃)₄] (1) and [Cu₅Gd₂(OH)₄(Br)₂-(H₂L)₂(H₃L)₂(NO₃)₂(OH₂)₄] (2), have been carried out to probe the origin of the large magnetocaloric effect (MCE). The magnetic exchange interactions for 1 and 2 via multiple pathways are estimated using DFT calculations. While the calculated exchange parameters deviate from previous experimental estimates obtained by fitting the magnetic data, the DFT parameter set is found to offer a striking match to the magnetic data for both complexes, highlighting the problem of overparameterization. Magnetostructural correlations for {Cu–Gd} pairs have been developed where both the Cu–O–Gd angles and Cu–O–Gd–O dihedral angles are found to significantly influence the magnitude and sign of the exchange constants. The magnitude of the MCE has been examined as a function of the exchange interactions, and clues on how the effect can be enhanced are discussed.

Herein we report a detailed investigation of the solid state and solution structures of lanthanide(III) complexes with the 18-membered pyridinophane ligand containing acetamide pendant arms TPPTAM (TPPTAM = 2,2′,2″-(3,7,11-triaza-1,5,9(2,6)-tripyridinacyclododecaphane-3,7,11-triyl)triacetamide). The ligand crystallizes in the form of a clathrated hydrate, where the clathrated water molecule establishes hydrogen-bonding interactions with the amide NH groups and two N atoms of the macrocycle. The X-ray structures of 13 different Ln³⁺ complexes obtained as the nitrate salts (Ln³⁺ = La³⁺–Yb³⁺, except Pm³⁺) have been determined. Additionally, the X-ray structure of the La³⁺ complex obtained as the triflate salt was also obtained. In all cases the ligand provides 9-fold coordination to the Ln³⁺ ion, ten coordination being completed by an oxygen atom of a coordinated water molecule or a nitrate or triflate anion. The bond distances of the metal coordination environment show a quadratic change along the lanthanide series, as expected for isostructural series of Ln³⁺ complexes. Luminescence lifetime measurements obtained from solutions of the Eu³⁺ and Tb³⁺ complexes in H₂O and D₂O point to the presence of a water molecule coordinated to the metal ion in aqueous solutions. The analysis of the Ln³⁺-induced paramagnetic shifts indicates that the complexes are ten-coordinated throughout the lanthanide series from Ce³⁺ to Yb³⁺, and that the solution structure is very similar to the structures observed in the solid state. The complexes of the light Ln³⁺ ions are fluxional due to a fast Δ(λλλλλλ) ↔ Λ(δδδδδδ) interconversion that involves the inversion of the macrocyclic ligand and the rotation of the acetamide pendant arms. The complexes of the small Ln³⁺ ions are considerably more rigid, the activation free energy determined from VT ¹H NMR for the Lu³⁺ complex being ΔG^⧧₂₉₈ = 72.4 ± 5.1 kJ mol^–1.

Single crystals of ScUS₃ were synthesized in high yield in a single step at 1173 K. ScUS₃ crystallizes in the FeUS₃ structure type in the space group D_2h¹⁷–Cmcm of the orthorhombic system with four formula units in a cell of dimensions a = 3.7500(8) Å, b = 12.110(2) Å, and c = 9.180(2) Å. Its structure consists of edge- and corner-sharing ScS₆ octahedra that form two-dimensional layers. U atoms between layers are connected to eight S atoms in a bicapped trigonal-prismatic fashion. ScUS₃ can be easily charge-balanced as Sc³⁺U³⁺(S^2–)₃ as there are no S–S single bonds present in the crystal structure. High temperature-dependent resistivity measurements on a single crystal of ScUS₃ show semiconducting behavior with an activation energy of 0.09(1) eV. A magnetic study on powdered single crystals of ScUS₃ reveals an antiferromagnetic transition at 198 K followed by a ferromagnetic transition at 75 K. The weak ferromagnetic behavior at low temperature may originate from canted antiferromagnetic spins. A density functional theory (DFT) calculation predicts ScUS₃ to be ferromagnetic and either a very poor metal or a semiconductor with a very small gap.

Visible-light persistent phosphors are commonly used as self-sustained night vision and fluorescence labeling materials. From the inspiration of the structure of six-membered rings plane in Ba₄(Si₃O₈)₂, a similar structure of Ba₅Si₈O₂₁ is expected that could exhibit more excellent phosphorescence property. In this Article, we report a novel visible long-lasting luminescence phosphor of Eu²⁺/Dy³⁺ codoped Ba₅Si₈O₂₁ for the first time. Ba₅Si₈O₂₁:Eu²⁺,Dy³⁺ phosphor could be activated effectively by sunlight or even in severe weather conditions, which is mainly attributed to the broad excitation spectrum (200–455 nm) and highly responds to UV-A and violet-light in the solar spectrum. After activation, Ba₅Si₈O₂₁:Eu²⁺,Dy³⁺ emits intense emission at 380–680 nm with persistent phosphorescence beyond 16 h. Moreover, it exhibits excellent and stable phosphorescence even in water, indicating that Ba₅Si₈O₂₁:Eu²⁺,Dy³⁺ will be a all-weather material that can be effectively and repeatedly charged by natural daylight in all kinds of open-air environments. Furthermore, the quantum tunneling behavior was illustrated in the afterglow mechanism.

The crystal structure of the wurtzite-derived β-CuGaO₂ was refined by Rietveld analysis of high-resolution powder diffraction data obtained from synchrotron X-ray radiation. Its structural characteristics are discussed in comparison with the other I–III–VI₂ and II–VI oxide semiconductors. The cation and oxygen tetrahedral distortions of the β-CuGaO₂ from an ideal wurtzite structure are small. The direct band-gap nature of the β-CuGaO₂, unlike β-Ag(Ga,Al)O₂, was explained by small cation and oxygen tetrahedral distortions. In terms of the thermal stability, the β-CuGaO₂ irreversibly transforms into delafossite α-CuGaO₂ at >460 °C in an Ar atmosphere. The transformation enthalpy was approximately −32 kJ mol^–1, from differential scanning calorimetry. This value is close to the transformation enthalpy of CoO from the metastable zincblende form to the stable rock-salt form. The monovalent copper in β-CuGaO₂ was oxidized to divalent copper in an oxygen atmosphere and transformed into a mixture of CuGa₂O₄ spinel and CuO at temperatures >350 °C. These thermal properties indicate that β-CuGaO₂ is stable at ≤300 °C in both reducing and oxidizing atmospheres while in its metastable form. Consequently, this material could be of use in optoelectronic devices that do not exceed 300 °C.

A new layered trigonal (P3̅1m) form of MnSb₂O₆, isostructural with MSb₂O₆ (M = Cd, Ca, Sr, Pb, and Ba) and MAs₂O₆ (M = Mn, Co, Ni, and Pd), was prepared by ion-exchange reaction between ilmenite-type NaSbO₃ and MnSO₄–KCl–KBr melt at 470 °C. It is characterized by Rietveld analysis of the X-ray diffraction pattern, electron microprobe analysis, magnetic susceptibility, specific heat, and ESR measurements as well as by density functional theory calculations. MnSb₂O₆ is very similar to MnAs₂O₆ in the temperature dependence of their magnetic susceptibility and spin exchange interactions. The magnetic susceptibility and specific heat data show that MnSb₂O₆ undergoes a long-range antiferromagnetic order with Néel temperature T_N = 8.5(5) K. In addition, a weak ferromagnetic component appears below T₁ = 41.5(5) K. DFT+U implies that the main spin exchange interactions are antiferromagnetic, thereby forming spin-frustrated triangles. The long-range ordered magnetic structure of MnSb₂O₆ is predicted to be incommensurate as found for MnAs₂O₆. On heating, the new phase transforms to the stable P321 form via its intermediate disordered variant.

In oxyfluoride chemistry, the [MO_xF_6–x]^2– anions (M = transition metal) are interesting polar building units that may be used to design polar materials, but their polar vs antipolar orientations in the solid state, which directly depend on the interactions between O^2–/F^– ligands and the extended structure, remain difficult to control. To improve this control, these interactions were assessed through crystallization of five related [MO_xF_6–x]^2– (M = Ti⁴⁺, V⁵⁺, Mo⁶⁺, W⁶⁺) anions with organic molecules. The hybrid organic–inorganic compounds, (4,4′-bpyH₂)TiF₆ (1), (enH₂)MoO₂F₄ (2), (4-hpyH)₂MoO₂F₄·H₂O (3), (4,4′-bpyH₂)WO₂F₄ (4), and (4,4′-bpyH₂)VOF₅ (5), exhibit isolated [MO_xF_6–x]^2– anions in a hydrogen bond network. The analysis of these crystal structures in combination with DFT calculations elucidate how differences in structure directing properties of these anions arise when π-overlap between O 2p orbitals and M d orbitals is weak and significantly affected by an increase of the energy of the d orbitals from 3d to 5d.

2-Aminophenol dioxygenases catalyze the oxidative ring cleavage of 2-aminophenol to 2-picolinic acid using O₂ as the oxidant. Inspired by the reaction catalyzed by these nonheme iron enzymes, a biomimetic iron(III)-2-amidophenolate complex, [(tBu-L^Me)Fe^III(4,6-di-tBu-AP)](ClO₄) (1a) of a facial tridentate ligand (tBu-L^Me = 1-[bis(6-methyl-pyridin-2-yl)-methyl]-3-tert-butyl-urea and 4,6-di-tBu-H₂AP = 2-amino-4,6-di-tert-butylphenol) bearing a urea group have been isolated. The complex reacts with O₂ to cleave the C–C bond of 4,6-di-tBu-AP regioselectively and catalytically to afford 4,6-di-tert-butyl-2-picolinic acid. An iron(II)-chloro complex [(tBu-L^Me)Fe^IICl₂(MeOH)] (1) of the same ligand also cleaves the aromatic ring of 4,6-di-tBu-AP catalytically in the reaction with O₂. To assess the effect of urea group on the ring cleavage reaction of 2-aminophenol, two iron complexes, [(BA-L^Me)₂Fe^II₂Cl₄] (2) and [(BA-L^Me)Fe^III(4,6-di-tBu-AP)](ClO₄) (2a), of a tridentate ligand devoid of urea group (BA-L^Me = benzyl-[bis(6-methyl-pyridin-2-yl)-methyl]-amine) have been isolated and characterized. Although the iron complexes (1 and 1a) of the ligand with urea group display catalytic reaction, the iron complexes (2 and 2a) of the ligand without urea group do not exhibit catalytic aromatic ring fission reactivity. The results support the role of urea group in directing the catalytic reactivity exhibited by 1 and 1a.

The synthesis, stability, and photophysical properties of [2 + 1] Re(I)/Tc(I) complexes derived from bipyridine and a series of imidazole derivatives were investigated as a means of identifying complexes suitable for creating targeted isostructural optical/nuclear molecular imaging probes. To prepare the desired complexes, [Re(CO)₃(H₂O)₃]Br was combined with 2,2′-bipyridine (bipy) to give [Re(CO)₃(bipy)Br], which in turn was converted to the desired complexes by treatment with functionalized imidazoles, yielding crystal structures of two new Re complexes. The corresponding ^99mTc complexes [^99mTc(CO)₃(bipy)(L)]⁺ (L = imidazole derivatives) were prepared by combining [^99mTc(CO)₃(bipy)(H₂O)]Cl with the same series of ligands and heating at 40 or 60 °C for 30 min. Quantitative transformation to the final products was confirmed in all cases by HPLC, and the nature of the complexes was verified by comparison to the authentic Re standards. Incubation in saline and plasma, and amino acid challenge experiments showed that N-substituted imidazole derivatives, bearing electron donating groups, exhibited superior stability to analogous metal complexes derived from less basic ligands. Imaging studies in mice revealed that with the appropriate choice of monodentate ligand, it is possible to prepare robust [2 + 1] Tc complexes that can be used as the basis for preparing targeted isostructural optical and nuclear probes.

Two crown ether complexes of sodium and potassium naphthalenolates were synthesized and entirely characterized. The two complexes can iso-selectively catalyze the ring-opening polymerization (ROP) of rac-lactide at room temperature and afford polylactides with desired molecular weights and narrow PDIs; the best isotacticity (P_m) achieved was 0.73.

By using a new resorcin[4]arene-based tetracarboxylate, three functional coordination polymers (CPs)—namely, [(CH₃)₂NH₂][Cd₂NaL(HCOO)₂(HCOOH)(H₂O)]·H₂O (1), [(CH₃)₂NH₂]₂[CdL]·CH₃OH·4H₂O (2), and [(CH₃)₂NH₂][Zn₂Na₃L₂(H₂O)₂]·H₂O (3)—have been synthesized under solvothermal conditions (H₄L = 2,8,14,20-tetra-pentyl-4,10,16,22-tetrakis((4-carboxybenzyl)oxy)-6,12,18,24-tetra-methoxy-resorcin[4]arene and DMF = N,N′-dimethylformamide). The structures of 1–3 have been confirmed by single-crystal X-ray diffraction analyses and further physically characterized. In 1, L and HCOO^– link Cd(II) and Na(I) ions to yield an unusual three-dimensional (3D) 4-connected heterometallic framework with (4²·6⁴)(4·8³·10·12) topology. In 2, L anions link Cd(II) ions to give a 3D binodal 4-connected framework with (4²·6³·8)₂ topology. In 3, adjacent dodecanuclear heterometallic clusters are joined together by L anions, yielding a two-dimensional (2D) (3,8)-connected (3·4²)(3⁴·4⁶·5⁶·6⁸·7³·8) network. Most strikingly, CPs 1 and 2 display unusual metal-ion exchange characters. CP 2 shows remarkable reversible adsoption of I₂ molecules. In addition, CPs 1–3 can selectively adsorb organic dyes and exhibit highly luminescent sensing properties for small molecules.

Two isostructural microporous zwitterionic metal–organic frameworks (ZW MOFs), {[M(bdcbpy)(OH₂)₄]·4H₂O}_n with M = Mn (1) and Ni (2), were synthesized by the rational design of the flexible anionic viologen derivate, 1,1′-bis(3,5-dicarboxybenzyl)-4,4′-bipyridinium dibromide dihydrate solvate (H₄bdcbpyBr₂·2H₂O), and its self-assembly with metal(II) acetates in an aqueous medium. Single-crystal structure analyses revealed that both compounds exhibit three-dimensional hydrogen-bonded supramolecular frameworks with one-dimensional channel pores. Significantly, the pore surfaces are lined with charge gradients employed by the ZW ligand bdcbpy^2– leading to the adsorption of hydrogen attributed to polarization effects. The thermostabilty and activation conditions were systematically investigated by thermogravimetric analysis, differential scanning calorimetry, and powder X-ray diffraction experiments. Furthermore, repeating cycles of reversible color changes are observed in air upon irradiation with UV light attributed to the formation of viologen radicals via an intermolecular electron transfer. This work also contains an in-depth literature analysis on ZW MOFs, which shows the need for the development of alternative routes for the rational design of new porous ZW MOFs.

In this paper we report a theoretical study of the CaSeO₄ compound at ambient pressure and under pressure. Here we made a structural analysis of its three known polymorphs—orthorhombic (Cmca), monoclinic monazite, and tetragonal scheelite—where direct comparison with experimental measurements is done. Besides, the electronic and vibrational structures are reported for the first time for those structures. In addition, the behavior of CaSeO₄ as a function of pressure is studied, where phase transitions are investigated by considering a quasiharmonic approximation at 300 K. After a total energy study of 14 possible high-pressure phases of CaSeO₄, the following sequence of pressure-driven structural transitions has been found: orthorhombic (Cmca) → tetragonal scheelite → monoclinic AgMnO₄-type structure. It was observed that monazite is less stable as temperature increases, while the opposite occurs for the AgMnO₄-type structure, this being a novel polymorph. This high-pressure structure is a distortion of the monazite structure and resembles the distorted barite-type structure (P2₁/n) of CaSO₄. The equation of state and the pressure evolution of the structural, electronic, and vibrational properties are also reported.

The first example of a ferrocene-chelating heteroscorpionate, [Li(THF)₂][fc(PPh₂)(BH[(3,5-Me)₂pz]₂)] ((fc^P,B)Li(THF)₂, fc = 1,1′-ferrocenediyl) is described. Starting from a previously reported compound, fcBr(PPh₂), a series of ferrocene derivatives, fc(PPh₂)(B[OMe]₂), [Li(OEt₂)][fc(PPh₂)(BH₃)], [Li(THF)₂][fc(PPh₂)(BH[(3,5-Me)₂pz]₂)] (pz = pyrazole), was isolated and characterized. Compound (fc^P,B)Li(THF)₂ allowed the synthesis of the corresponding nickel and zinc complexes, (fc^P,B)NiCl, (fc^P,B)NiMe, (fc^P,B)ZnCl, and (fc^P,B)ZnMe. All compounds were characterized by NMR spectroscopy, while the zinc and nickel complexes were also characterized by X-ray crystallography. The redox behavior of (fc^P,B)NiCl, (fc^P,B)NiMe, (fc^P,B)ZnCl, and (fc^P,B)ZnMe was studied by cyclic voltammetry and supported by density functional theory calculations.

Intentional incorporation of defect sites functionalized with free carboxylic acid groups was achieved in a paddlewheel-based metal–organic framework (MOF) of rht topology, NU-125. Solvent-assisted linker exchange (SALE) performed on a mixed-linker derivative of NU-125 containing isophthalate (IPA) linkers (NU-125-IPA) led to the selective replacement of the IPA linkers in the framework with a conjugate base of trimesic acid (H₃BTC). Only two of the three carboxylic acid moieties offered by H₃BTC coordinate to the Cu₂ centers in the MOF, yielding a rare example of a MOF decorated with free −COOH groups. The presence of the −COOH groups was confirmed by diffuse reflectance infrared Fourier-transformed spectroscopy (DRIFTS); moreover, these groups were found to be available for postsynthesis elaboration (selective monoester formation). This work constitutes an example of the use of SALE to obtain otherwise challenging-to-synthesize MOFs. The resulting MOF, in turn, can serve as a platform for accomplishing selective organic transformations, in this case, exclusive monoesterification of trimesic acid.

We focus here on the properties of Fe complexes formed with Schiff bases involved in the chemistry of Fe^III spin-transition archetypes. The neutral Fe(pap-5NO₂)₂ (1) and Fe(qsal-5NO₂)₂·Solv (2 and 2·Solv) compounds (Solv = 2H₂O) derive from the reaction of Fe^II salts with the condensation products of pyridine-2-carbaldehyde with 2-hydroxy-5-nitroaniline (Hpap-5NO₂) or 5-nitrosalicylaldehyde with quinolin-8-amine (Hqsal-5NO₂), respectively. While the Fe(qsal-5NO₂)₂·Solv solid is essentially low spin (S = 0) and requires temperatures above 300 K to undergo a S = 0 ↔ S = 2 spin-state switching, the Fe(pap-5NO₂)₂ one presents a strongly cooperative first-order transition (T↓ = 291 K, T↑ = 308 K) centered at room temperature associated with a photomagnetic effect at 10 K (T_LIESST = 58 K). The investigation of these magnetic behaviors was conducted with single-crystal X-ray diffraction (1, 100 and 320 K; 2, 100 K), Mössbauer, IR, UV–vis (1 and 2·Solv), and differential scanning calorimetry (1) measurements. The Mössbauer analysis supports a description of these compounds as Fe^II Schiff-base complexes and the occurrence of a metal-centered spin crossover process. In comparison with Fe^III analogues, it appears that an expanded coordination sphere stabilizes the valence 2+ state of the Fe ion in both complexes. Strong hydrogen-bonding interactions that implicate the phenolato group bound to Fe^II promote the required extra-stabilization of the S = 2 state and thus determines the spin transition of 1 centered at room temperature. In the lattice, the hydrogen-bonded sites form infinite chains interconnected via a three-dimensional network of intermolecular van der Waals contacts and π–π interactions. Therefore, the spin transition of 1 involves the synergetic influence of electrostatic and elastic interactions, which cause the enhancement of cooperativity and result in the bistability at room temperature.

In an aqueous solution, photophysical, photochemical, and photocatalytic abilities of a Ru(II)–Re(I) binuclear complex (RuReCl), of which Ru(II) photosensitizer and Re(I) catalyst units were connected with a bridging ligand, have been investigated in details. RuReCl could photocatalyze CO₂ reduction using ascorbate as an electron donor, even in an aqueous solution. The main product of the photocatalytic reaction was formic acid in the aqueous solution; this is very different in product distribution from that in a dimethylformamide (DMF) and triethanolamine (TEOA) mixed solution in which the main product was CO. A ¹³CO₂ labeling experiment clearly showed that formic acid was produced from CO₂. The turnover number and selectivity of the formic acid production were 25 and 83%, respectively. The quantum yield of the formic acid formation was 0.2%, which was much lower, compared to that in the DMF–TEOA mixed solution. Detail studies of the photochemical electron-transfer process showed back-electron transfer from the one-electron-reduced species (OERS) of the photosensitizer unit to an oxidized ascorbate efficiently proceeded, and this should be one of the main reasons why the photocatalytic efficiency was lower in the aqueous solution. In the aqueous solution, ligand substitution of the Ru(II) photosensitizer unit proceeded during the photocatalytic reaction, which was a main deactivation process of the photocatalytic reaction. The product of the ligand substitution was a Ru(II) bisdiimine complex or complexes with ascorbate as a ligand or ligands.