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 degrees 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(mu4-S)(mu-S2)4Br8]. The tantalum atoms form a square with long Ta...Ta distances (3.30 angstroms), 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-mu4-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.