Synthesis and Structure of Ta₄S₉Br₈. An Emergent Family of Early Transition Metal Chalcogenide Clusters

Single crystals of Ta4S9Br8 are obtained by heating Ta, S, and Br2 at 400 °C in a 4.0:9.0:4.0 molar ratio in a 44% yield. The structure was determined by X-ray analysis and consists of molecular clusters [Ta4(μ4-S)(μ-S2)4Br8]. The tantalum atoms form a square with long Ta···Ta distances (3.30 Å), with four S2 ligands bridging the Ta−Ta edges and one capping the square. Each Ta atom has two terminal bromine atoms. The compound is diamagnetic and has only two electrons for metal−metal bonding. IR and Raman spectral studies with the use of 34S allow to identify characteristic vibrations S−S (537 cm-1) and Ta4-μ4-S (407 cm-1). The compound is soluble in CH3CN, giving a dark-red solution with a characteristic electronic spectrum, which was assigned on the base of DFT calculations. ESI-MS spectra of the solutions show formation of {[Ta4S9Br8]Br}- associates.