Synthesis and structure of two octahedral molybdenum chloride sulfide clusters

Abstract

A preparation for chloride sulfide Mo/sub 6/X/sub 8/ clusters has been devised which employs substitution by sulfide into the Mo/sub 6/Cl/sub 8//sup 4 +/ cluster. The Mo/sub 6/Cl/sub 7/S/sup 3 +/ cluster has been isolated in the two compounds (C/sub 5/H/sub 5/NH)/sub 3/((Mo/sub 6/Cl/sub 7/S)Cl/sub 6/) x 3(C/sub 5/H/sub 5/NH)Cl and (C/sub 5/H/sub 5/NH)/sub 3/((Mo/sub 6/Cl/sub 7/S)Cl/sub 6/). The structures of both compounds were determined by single crystal x-ray techniques. Despite the different site symmetries of the (Mo/sub 6/Cl/sub 7/S)Cl/sub 6//sup 3 -/ units in the two compounds (S/sub 6/ in the former, C/sub i/ in the latter), corresponding average bond distances and angles are equivalent. The infrared spectra (200 to 450 cm/sup -1/) of the two compounds are identical, and exhibit a band at 421 cm/sup -1/ assigned to a (Mo/sub 6/Cl/sub 7/S)Cl/sub 6//sup 3 -/ cluster vibration of predominant Mo-S character. Resolution of the chlorine 2p photoelectron spectra into components reveals not only that sulfide occupies a bridging ligand site of the (Mo/sub 6/Cl/sub 7/S)Cl/sub 6//sup 3 -/ cluster, but also that the difference between the chlorine 2p binding energies of the bridging and terminal chlorides is anomalously small. The Mo/sub 6/S/sub 6/Cl/sub 2/ cluster has been isolatedmore » in the novel compound (Mo/sub 6/S/sub 6/Cl/sub 2/)(NC/sub 5/H/sub 5/)/sub 6/. The structure, determined by single crystal x-ray techniques, consists of an approximately cubic Mo/sub 6/X/sub 8/ cluster with six terminal pyridine ligands. (Mo/sub 6/S/sub 6/Cl/sub 2/)(NC/sub 5/H/sub 5/)/sub 6/ is the first example of a Mo/sub 6/X/sub 8/ cluster with terminal ligands which has fewer that 24 electrons in its metal-metal bonding orbitals. X-ray powder data indicates this compound may be one composition in a molecular solid solution (Mo/sub 6/S/sub 7-x/Cl/sub 1+x/)(NC/sub 5/H/sub 5/)/sub 6/(0 less than or equal to x less than or equal to 2).« less