Cs2Ln3CuS8 (Ln = La-Nd, Sm-Tb): Synthesis, Crystal Structure, and Magnetic and Optical Properties.

This work reports the preparation of new quaternary sulfides Cs2Ln3CuS8 (Ln = La-Nd, Sm-Tb), their original crystal and electronic structures, and their magnetic properties. The sulfides were prepared using a reactive flux method from mixtures of Ln2S3 (EuS), Cs2S6, Cu2S, and S. They crystallize in a new type of structure (C2/m space group) and exhibit a layer-like crystal structure, which is a hybrid of those of the ACe2CuS6 series (A = Cs, K) and that of K2CeCu2S4. The values of the optical band gap calculated by the Kubelka-Munk equation are in the range of 1.2-2.62 eV depending on the nature of the Ln ion. The Cs2Gd3CuS8 compound displays relatively great magnetic refrigerating properties at cryogenic temperature with the mass entropy change (-ΔSM) reaching 19.5 J kg-1 K-1 at 3.5 K for ΔH = 5 T.

Replenishment in the Family of Rhenium Chalcobromides; Synthesis and Structure of Molecular {Re4S4}Br8(TeBr2)4, Dimeric [{Re4S4}Br8(TeBr2)3]2, and Polymeric {Re4S4}Br8 Compounds Based on the {Re4S4}8+ Tetrahedral Cluster Core.

We have obtained three new rhenium(IV) chalcobromides belonging to the homologous series {Re4S4}Br8(TeBr2)n (n = 0, 3, 4): a molecular complex {Re4S4}Br8(TeBr2)4 (1), a dimeric complex [{Re4S4}(TeBr2)3Br7(µ-Br)]2 (2), and a two-dimensional (2D) polymeric compound {Re4S4}Br8 (3). Compound 1 is isotypic to the already known {Re4Te4}(TeBr2)4Br8, while 2 and 3 exhibit a new type of binding of tetrahedral clusters via µ-Br bridges. Compounds were characterized by X-ray single-crystal diffraction, X-ray powder diffraction, and thermal and elemental analyses. In compound 2, two tetrahedral cluster cores {Re4S4}8+ are linked together forming a dimer through two Re-µ-Br-Re bridges. Calculations of the electron localization function (ELF) showed that there is no covalent interaction between rhenium atoms of neighboring clusters. In compound 3, each rhenium atom of the {Re4S4}8+ core is coordinated by three Br ligands: one terminal Br and two bridging µ-Br ligands. As a result, eight bridging bromine atoms link {Re4S4}8+ cluster cores into goffered layers. {Re4S4}Br8 is the new stable rhenium(IV) thiobromide, the first discovered in the Re-S-Br system, along with the already known octahedral rhenium(III) thiobromides Re6S4+xBr10-2x (x = 0-4).

Synthesis, Structure, and Spectroscopic Study of Redox-Active Heterometallic Cluster-Based Complexes [Re5MoSe8(CN)6]n.

The heterometallic cluster-based compound K5[Re5MoSe8(CN)6] was obtained by high-temperature reaction from a mixture of ReSe2 and MoSe2 in molten potassium cyanide. The redox behavior of the [Re5MoSe8(CN)6]5- cluster anion was studied by cyclic voltammetry in aqueous and organic media showing two reversible one-electron-redox transitions with E1/2 of -0.462 and 0.357 V versus Ag/AgCl in CH3CN. Aqueous media potentials were found to be noticeably shifted to higher values because of solvation. Chemically accessible potentials allowed us to structurally isolate and characterize the [Re5MoSe8(CN)6]n (n = 3-, 4-, and 5-) cluster complex in several charge states with corresponding cluster skeletal electron (CSE) numbers ranging from 24 to 22. The electronic absorption of the [Re5MoSe8(CN)6]n cluster complex varies significantly upon a change of the CSE number, especially in the visible and near-IR regions. The local cluster core distortion upon electron removal was confirmed by density functional theory calculation, while the overall geometry of the cluster anion remained practically unaltered.

Supramolecular Frameworks Based on Rhenium Clusters Using the Synthons Approach.

The reaction of the K4[{Re6Si8}(OH)a6]·8H2O rhenium cluster salt with pyrazine (Pz) in aqueous solutions of alkaline or alkaline earth salts at 4 °C or at room temperature leads to apical ligand exchange and to the formation of five new compounds: [trans-{Re6Si8}(Pz)a2(OH)a2(H2O)a2] (1), [cis-{Re6Si8}(Pz)a2(OH)a2(H2O)a2] (2), (NO3)[cis-{Re6Si8}(Pz)a2(OH)a(H2O)a3](Pz)·3H2O (3), [Mg(H2O)6]0.5[cis-{Re6Si8}(Pz)a2(OH)a3(H2O)a]·8.5H2O (4), and K[cis-{Re6Si8}(Pz)a2(OH)a3(H2O)a]·8H2O (5). Their crystal structures are built up from trans- or cis-[{Re6Si8}(Pz)a2(OH)a4-x(H2O)ax]x-2 cluster units. The cohesions of the 3D supramolecular frameworks are based on stacking and H bonding, as well as on H3O2-bridges in the cases of (1), (2), (4), and (5) compounds, while (3) is built from stacking and H bonding only. This evidences that the nature of the synthons governing the cluster unit assembly is dependent on the hydration rate of the unit.

Tailoring Heterometallic Cluster Functional Building Blocks: Synthesis, Separation, Structural and DFT Studies of [Re6-x Mox Se8 (CN)6 ]n.

Influence of the metal core composition and geometry on the structure, spectroscopic properties and redox potentials was investigated for the first time for heterometallic (Re/Mo)6 octahedral clusters. The discrete anionic clusters [Re6-x Mox Se8 (CN)6 ]n- (x=2, 3; n=4, 5) were obtained as individual salts. Their isomeric composition and bond-length distribution were inspected using a combination of single-crystal X-ray structure analysis, NMR, EXAFS, and DFT calculations.

Host-Guest Binding Hierarchy within Redox- and Luminescence-Responsive Supramolecular Self-Assembly Based on Chalcogenide Clusters and γ-Cyclodextrin.

Water-soluble salts of anionic [Re6 Q8 (CN)6 ]4- (Q=S, Se, Te) chalcogenide octahedral rhenium clusters react with γ-cyclodextrin (γ-CD) producing a new type of inclusion compounds. Crystal structures determined through single-crystal X-ray diffraction analysis revealed supramolecular host-guest assemblies resulting from close encapsulations of the octahedral cluster within two γ-CDs. Interestingly, nature of the inner Q ligands influences strongly the host-guest conformation. The cluster [Re6 S8 (CN)6 ]4- interacts preferentially with the primary faces of the γ-CD while the bulkier clusters [Re6 Se8 (CN)6 ]4- and [Re6 Te8 (CN)6 ]4- exhibit specific interactions with the secondary faces of the cyclic host. Furthermore, analysis of the crystal packing reveals additional supramolecular interactions that lead to 2D infinite arrangements with [Re6 S8 (CN)6 ]4- or to 1D "bamboo-like" columns with [Re6 Se8 (CN)6 ]4- and [Re6 Te8 (CN)6 ]4- species. Solution studies, using multinuclear NMR methods, ESI-MS and Isothermal titration calorimetry (ITC) corroborates nicely the solid-state investigations showing that supramolecular pre-organization is retained in aqueous solution even in diluted conditions. Furthermore, ITC analysis showed that host-guest stability increases significantly ongoing from S to Te. At last, we report herein that deep inclusion alters significantly the intrinsic physical-chemical properties of the octahedral clusters, allowing redox tuning and near IR luminescence enhancement.

Synthesis, Crystal Structure, and Liquid Exfoliation of Layered Lanthanide Sulfides KLn2CuS6 (Ln = La, Ce, Pr, Nd, Sm).

Among the great amount of known lanthanide nanoparticles, reports devoted to chalcogenide ones are deficient. The properties of such nanoparticles remain almost unknown due to the lack of simple and proper synthetic methods avoiding hydrolysis and allowing preparation of oxygen-free lanthanide nanoparticles. A liquid exfoliation method was used to select the optimum strategy for the preparation of quaternary lanthanide sulfide nanoparticles. Bulk KLn2CuS6 (Ln = La-Sm) materials were obtained via a reactive flux method. The crystal structures of three new members of the KLn2CuS6 series were determined for Pr, Nd, and Sm as well as for known KLa2CuS6. KLn2CuS6 (Ln = La, Pr, Nd) compounds crystallize in the monoclinic C2 /c space group, whereas KSm2CuS6 crystallizes in the orthorhombic Fddd space group. The analysis of their electronic structures confirms that the main bonding interactions occur within the anionic {Ln2CuS6}- layers. Due to their layered structure, exfoliation of these compounds is possible using ultrasonic treatment in appropriate solvents with the formation of colloidal solutions. Colloidal particles show a plate-like morphology with a lateral size of 100-200 nm and a thickness of 2-10 nm. Highly negative or positive charges found in isopropanol and acetonitrile dispersions, respectively, are associated with high stability and concentration of the dispersions.

Metal Atom Clusters as Building Blocks for Multifunctional Proton-Conducting Materials: Theoretical and Experimental Characterization.

The search for new multifunctional materials displaying proton-conducting properties is of paramount necessity for the development of electrochromic devices and supercapacitors as well as for energy conversion and storage. In the present study, proton conductivity is reported for the first time in three molybdenum cluster-based materials: (H)4[Mo6Br6S2(OH)6]-12H2O and (H)2[Mo6X8(OH)6]-12H2O (X = Cl, Br). We show that the self-assembling of the luminescent [Mo6L8i(OH)6a]2-/4- cluster units leads to both luminescence and proton conductivity (σ = 1.4 × 10-4 S·cm-1 in (H)2[Mo6Cl8(OH)6]-12H2O under wet conditions) in the three materials. The latter property results from the strong hydrogen-bond network that develops between the clusters and the water molecules and is magnified by the presence of protons that are statistically shared by apical hydroxyl groups between adjacent clusters. Their role in the proton conduction is highlighted at the molecular scale by ab initio molecular dynamics simulations that demonstrate that concerted proton transfers through the hydrogen-bond network are possible. Furthermore, thermogravimetric analysis also shows the ability of the compounds to accommodate more or less water molecules, which highlights that vehicular (or diffusion) transport probably occurs within the materials. An infrared fingerprint of the mobile protons is finally proposed based on both theoretical and experimental proofs. The present study relies on a synergic computational/experimental approach that can be extended to other proton-conducting materials. It thus paves the way to the design and understanding of new multifunctional proton-conducting materials displaying original and exciting properties.

Synthesis and characterization of A4[Re6Q8L6]@SiO2 red-emitting silica nanoparticles based on Re6 metal atom clusters (A = Cs or K, Q = S or Se, and L = OH or CN).

Metal atom clusters constitute very promising candidates as luminophores for applications in biotechnology because they are nanosized entities offering robust luminescence in the near-infrared field (NIR). However, they cannot be used as prepared for biological applications because of potential toxic effects and quenching of the clusters' luminescence in aqueous media, and they therefore need to be dispersed in a biocompatible matrix. We describe herein the encapsulation of octahedral rhenium clusters, denoted as A(4)[Re(6)Q(8)L(6)] (A = Cs or K, Q = S or Se, and L = OH or CN), in silica nanoparticles by a water-in-oil microemulsion process, paying particular attention to the clusters' stability. The obtained A(4)[Re(6)Q(8)L(6)]@SiO(2) nanoparticles are 30 nm in size with good monodispersity and a perfectly spherical shape, as shown by scanning electron microscopy (SEM). The presence of cluster units inside the silica matrix was evidenced by scanning transmission electron microscopy in annular dark-field mode (ADF-STEM). From the point of view of their optical properties, the A(4)[Re(6)Q(8)L(6)]@SiO(2) nanoparticles show red and NIR emission under UV excitation, even when dispersed in water. The evolution of the structural and luminescence properties of clusters before and after encapsulation was followed by Raman and photoluminescence spectroscopy.

Unusual H-bonding in novel cyano-cluster polymeric hydrates [(H){Ln(H2O)4}{Re6S8(CN)6}]*2H2O (Ln = Yb, Lu).

X-Ray studies and (1)H NMR measurements for novel cyano-bridged polymers [(H){Ln(H(2)O)(4)}{Re(6)S(8)(CN)(6)}]*2H(2)O (Ln = Yb, Lu) reveal temperature dependence of proton localization: acid protons are trapped between nitrogen atoms at low temperatures, but can be transferred to the water sublattice at higher temperatures; this transfer resulted in intermolecular proton exchange.

Mixed-metal clusters with a {Re3Mo3Se8} core: from a polymeric solid to soluble species with multiple redox transitions.

Cluster compounds based on a new {Re3Mo3Se8}n core were obtained and studied. The polymeric solid K6[Re3Mo3Se8(CN)4(CN)2/2] (1) containing 24 cluster valence electrons (CVE) was isolated as a result of high-temperature reaction. Water-soluble salts K5[Re3Mo3Se8(CN)6]·11H2O (2) and Cs5[Re3Mo3Se8(CN)6]·H2O (3) were prepared from compound 1. Crystal structures of the diamagnetic compounds 2 and 3 contain a cluster anion [Re3Mo3Se8(CN)6]5- with a 22-electronic core {Re3Mo3Se8}+. Metathesis reaction followed by recrystallization from CH3CN yielded paramagnetic salt (Ph4P)4[Re3Mo3Se8(CN)6]·2CH3CN (4) containing the {Re3Mo3Se8}2+ core with 21 CVE. Cyclic voltammetry of the solution of 4 displayed three quasi-reversible waves with E1/2 = -0.325, -0.818 and -1.410 V vs. Ag/AgCl electrode indicating the presence of [Re3Mo3Se8(CN)6]4-/5-/6-/7- transitions. Electronic structure calculations showed that both mer- and fac-isomers of [Re3Mo3Se8(CN)6]n- clusters undergo great distortion when the number of CVE decreases.

Stabilization of Ni2+ dimers in hexacyano Mo6 cluster-based Prussian blue derivatives: experimental and theoretical investigations of magnetic properties.

Herein, two new octahedral molybdenum cyanide cluster compounds, namely [{Ni(NH3)6}4{Ni2(NH3)8}1][Mo6Br6Q2(CN)6]3·12H2O, Q = S (1) and Se (2), have been synthesized as single crystals by slow diffusion of a solution of nickel chloride into aqueous ammonia solutions of a K2Cs2[Mo6Br6Q2(CN)6] molybdenum cyanide cluster-based compound. Both 1 and 2 were structurally characterized by single-crystal X-ray diffraction. They are isostructural and crystallize in the cubic system (Im3[combining macron]m (no. 229); Z = 2, a = 18.147(1) Å, and V = 5976(1) Å3 and a = 18.188(2) Å and V = 6016(2) Å3 for 1 and 2, respectively). 1 and 2 are based on the association of [Mo6Bri6Qi2(CN)a6]4- (Q = S, Se) cluster anions with Ni2+ dimer-based cubic [Ni2(NH3)8]4+ and octahedral [Ni(NH3)6]2+ cations. The structure is based on 2-fold interpenetrated [{Ni(NH3)6}4{Ni2(NH3)8}1][Mo6Br6Q2(CN)6]3 frameworks related to each other by [½, ½, ½] translation. The unit cell is based on a body-centered cubic framework of cubic [Ni2(NH3)8]4+. The [Mo6Bri6Qi2(CN)a6]4- (Q = S, Se) cluster units are located in the middle of the edges and at the center of the faces of the cell. The [{Ni(NH3)6}]2+ cations are located at the center of the cubes of the a/2 edge. The dimers [Ni2(NH3)8]4+ are stabilized by hydrogen bonds between the cyanide ligands of the cluster unit and the hydrogen atoms of the ammonia molecules. Both compounds exhibit a weak antiferromagnetic coupling within the [Ni2(NH3)8]4+ dimer entities at low temperatures together with a paramagnetic behavior originating from the cations of the octahedral [{Ni(NH3)6}]2+ complexes.

Versatility of the ionic assembling method to design highly luminescent PMMA nanocomposites containing [M6Q(i)8L(a)6](n-) octahedral nano-building blocks.

New luminescent poly(methylmethacrylate) (PMMA) nanocomposites with high content of different hexanuclear octahedral cluster building blocks, namely [Mo6I8(C2F5COO6)](2-), [Re6Se8(CN)6](4-) and [W6Cl14](2-) have been prepared by free-radical polymerisation. To do so, cluster complexes bearing a polymerisable ammonium counter-cation have been synthesised. In this way, we demonstrate that ionic assembling is a powerful tool to functionalise easily any type of anionic cluster units to be introduced in a PMMA organic matrix. All samples remain homogeneous, stable during several months, and retain the luminescence properties of the cluster precursor.

Heterometallic clusters with a new {Re3Mo3S8} core: direct synthesis, properties and DFT calculations.

We report the direct facile high-temperature synthesis and investigation of heterometallic rhenium-molybdenum cluster K6[Re3Mo3S8(CN)4(CN)2/2] (1) with a new {Re3Mo3S8} core. Dissolution of polymeric compound 1 resulted in subsequent oxidation and formation of stable 23e paramagnetic anionic cluster complex [Re3Mo3S8(CN)6](6-).