Mechanism of substitution on trinuclear incomplete cuboidal [M3X4(OH2)9]4+ ions: kinetic studies of water exchange and substitution by Cl? on [Mo3S4(OH2)9]4+

Abstract

The complex [Mo3S4(OH2)9]4+ possesses non-equivalent H2O ligands with those (d, two per Mo) which are trans to µ-S undergoing water exchange 103 faster than those (c, one per Mo) which are trans to µ3-S. The former arises from a labilising pathway involving the monohydroxo conjugate base [Mo3S4-(OH2)8(OH)]3+(KaM≈ 0.2 mol dm–3). The chloride anation reaction has also been studied and comparisons are made with data previously reported for the thiocyanate anation. Together the results suggest an ld mechanism for substitution at the d sites on [Mo3S4(OH2)8(OH)]3+. For water exchange on [Mo3S4(OH2)9]4+ at both the d and c sites, an la mechanism is tentatively suggested from comparisons with complex-formation data.