A Novel Tantalum Cluster Chalcohalide Ta4S1.5Se7.5I8

Single crystals of Ta₄S_1.5Se_7.5I₈ are obtained by heating Ta, S, Se and I₂ at 300 °C in 4.0:1.0:8.0:4.4 molar ratio. The structure was determined by X-ray analysis and consists of molecular clusters Ta₄(μ₄-S)(μ₂-Q_axSe_eq)₄I₈] (Q ≈ Se_0.87S_0.13). The tantalum atoms form a square with long Ta…Ta distances (3.26–3.32 Å), with four dichalcogenide ligands bridging the Ta–Ta edges and a sulfur atom capping the square. Each Ta atom has two terminal iodine atoms. Raman spectroscopy study shows the presence of the characteristic absorption band at 396 cm^?1 which is due to the Ta₄–μ₄-S vibrations. Cyclic voltammetry shows that Ta₄S_1.5Se_7.5I₈ in solid state undergoes quasi-reversible one-electron oxidation which is metal-centered.