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 Br-2 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 (Ta-4(mu(4)-S)(mu-S-2)(4)Br-8]. The tantalum atoms form a square with long (TaTa)-Ta-... distances (3.30 angstrom), with four S-2 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 S-34 allow to identify characteristic vibrations S-S (537 cm(-1)) and Ta-4-mu(4)-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.