Introduction of Niobium in the Chemistry of Octahedral Chalcogenide Clusters: Synthesis and Detailed Study of Compounds Based on Condensed and Discrete {Re5NbQ8} (Q = S or Se) Cores

It is known that niobium practically does not form cluster chalcogenide compounds of the {M6(μ3-Q8)} type, which are widespread in the chemistry of group 6 and 7 metals. This work reports the preparation of a series of polymeric and discrete niobium-containing heterometallic clusters based on the {Re5Nb(μ3-S8)} and {Re5Nb(μ3-Se8)} cores. The compounds were prepared by the high-temperature reaction between rhenium and niobium dichalcogenides in a KCN melt. The 1D polymers K5[Re5NbQ8(CN)5] (Q = S or Se), which were formed as a result of the reaction, crystallize in the structural type of K6[Mo6Se8(CN)5], similar to the previously reported heterometallic clusters K6[Re6-xMoxQ8(CN)5] (x = 2-3). The polymers were solubilized to form discrete anionic clusters [Re5NbQ8(CN)6]4-. The structure and properties of the new clusters were investigated using a combination of X-ray diffraction analysis, UV/vis spectroscopy, high-resolution electrospray mass spectrometry, cyclic voltammetry, and DFT calculations. Among other features, the compounds showed high electrochemical activity, being able to form three redox states in solution with reversible transitions. It was found that redox potentials of the isoelectronic octahedral clusters demonstrate a strong cathodic shift in the sequence [Re5OsSe8(CN)6]3- > [Re6Se8(CN)6]4- > [Re5MoSe8(CN)6]5- > [Re5NbSe8(CN)6]6-, illustrating the effect of systematic changes in the composition of octahedral cluster cores on their properties.

From K6[Re6-xMoxS8(CN)5] Solid Solution to Individual Cluster Complexes: Separation and Investigation of [Re4Mo2S8(CN)6]n- and [Re3Mo3S8(CN)6]n- Heterometallic Clusters

A series of new cluster compounds with {Re4Mo2S8} and {Re3Mo3S8} cores has been obtained and investigated. The clusters with different Re/Mo ratios were isolated as individual compounds, which made it possible to study their spectroscopic and electrochemical properties. The geometry of the new clusters was studied using a combination of X-ray diffraction analysis, XAS and quantum chemical DFT calculations. It was shown that the properties of the new clusters, such as the number and position of electrochemical transitions, electronic structure and change in geometry with a change in charge, are similar to the properties of clusters based on the {Re4Mo2Se8} and {Re3Mo3Se8} cores described earlier.

Heterometallic Re/Mo and Re/W cubane-type cluster complexes

A series of heterometallic Re/Mo and Re/W cubane-type cluster complexes were obtained. New cluster anions demonstrate a regular change in geometric characteristics and redox potentials depending on the composition of the cluster core.

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 E_1/2 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.

Stabilization of interpenetrating cluster-based frameworks promoted by N–H⋯X hydrogen bonds: synthesis, structures and properties of {[Cd(NH3)4]3[Re3Mo3Se8(CN)6]}X (X = Cl, Br and I)

Interpenetrating frameworks {[Cd(NH₃)₄]₃[Re₃Mo₃Se₈(CN)₆]}X (X = Cl, Br, I) driven by N–H⋯X bonding exhibit remarkable stability and reversible transitions in the solid state.