MECHANISM OF SUBSTITUTION ON TRINUCLEAR INCOMPLETE CUBOIDAL [M3X4(OH2)9]4- KINETIC-STUDIES OF WATER EXCHANGE AND SUBSTITUTION BY CL- ON [MO3S4(OH2)9]4+( IONS )

The complex [Mo3S4(OH2)9]4+ possesses non-equivalent H2O ligands with those (d, two per Mo) which are trans to mu-S undergoing water exchang e 10(5) faster than those (c, one per Mo) which are trans to mu3-S. Th e former arises from a labilising pathway involving the monohydroxo co njugate base [Mo3S4-(OH2)8(OH)]3+ (K(aM) almost-equal-to 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. To gether the results suggest an 1, mechanism for substitution at the d s ites on [Mo3S4(OH2)8(OH)]3+. For water exchange on [Mo3S4(OH2)9]4+ at both the d and c sites, an I(a) mechanism is tentatively suggested fro m comparisons with complex-formation data.