Solution studies on the triangular incomplete cuboidal dimolybdenum-tungsten cluster aqua ion [Mo2W(µ3-O)(µ-O)3(OH2)9]4+; crystal structure of [NMe4]5[Mo2W(µ3-O)(µ-O)3(NCS)9]·C6H5Me

Abstract

The synthesis and structural characterisation of the triangular incomplete cuboidal dimolybdenum-tungsten cluster aqua ion [Mo₂W(µ₃-O)(µ-O)₃(OH₂)₉]⁴⁺ is reported. An X-ray crystallographic study of the derivative complex [NMe₄]₅[Mo₂W(µ₃-O)(µ-O)₃(NCS)₉]·C₆H₅Me shows positional disorder at the Mo and W atoms resulting in crystallographically identical metal sites ⅔ Mo and ⅓ W in character. Oxygen-17 and molybdenum-95 NMR measurements coupled with redox studies have verified the presence of the mixed cluster in solution. A kinetic study with regard to 1:1 NCS^– substitution at the water ligands is supportive of reaction occurring at one of the two more labile and statistically identical and independent molybdenum sites promoted through a conjugate base form presumed to derive via deprotonation of a water ligand trans to the µ-O groups on the same molybdenum atom. Electronic effects on the redox and substitution behaviour at molybdenum arising from the presence of the remote tungsten atom have been detected.