SYNTHESIS, CHARACTERIZATION AND ELECTRONIC-STRUCTURE OF TRINUCLEAR COMPLEXES POSSESSING A HEXATHIOLATO-MOLYBDENUM(IV) OR HEXASELENOLATOTUNGSTEN(IV) CORE

Reaction of [MoCl4(SMe2)2] with thiolate and [{Cu(PPh3)Cl}4] in toluene or chlorobenzene affords trinuclear heterobimetallic clusters [(Ph3P)Cu(mu-SR)3Mo(mu-SR)3Cu(PPh3)] (R = C6H4Me-4 2, C6H4F- 4 3, C6H4Cl-4 4 or C6H4Br-4 5). In a similar synthesis using selenolate and [WCl4(SMe2)2] a cluster containing the novel hexaselenolatotungsten(IV) core was obtained. The identity of all compounds was confirmed by NMR spectroscopy. Recrystallization from tetrahydrofuran yields X-ray quality crystals. The crystal structure of 2 has been determined by single-crystal X-ray diffraction. The crystals are rhombohedral, space group R3BAR, with a = 14.988(5) angstrom, alpha = 107.17(3)degrees and Z = 1. The paramagnetic complex consists of an approximately octahedral hexathiolatomolybdenum(IV) dianion, with two parallel faces of the octahedron capped by triphenylphosphinecopper(I) cations. The Mo-Cu distance of 269.1 (1) pm is indicative of some degree of metal-metal bonding. The presence of a dative bond from the d10 Cu to the d2 Mo was confirmed by density functional calculations. However, the major contribution to the overall bonding energy stems from the electrostatic attraction between the two metal fragments.