Novel Methanol‐Containing Oxomolybdate(V) Complexes: Synthesis and Structural Characterisation of Intermediates in the Formation of {Mo2O4}2+ Clusters from [MoOCl4(H2O)]– and [MoOBr4]– Precursors

Abstract

AbstractA series of oxomolybdate(V) complexes with methanol was prepared by the reaction of (PyH)5[MoOCl4(H2O)]3Cl2 (1) or (PyH)[MoOBr4] (PyH+ = pyridinium cation, C5H5NH+) in methanol. (PyH)2[MoOCl4(MeOH)]Cl (2) is obtained upon substitution of coordinated water for methanol in 1. Small amounts of weak bases such as pyridine or trifluoroacetate promote further substitution chemistry at the labile sites, followed by dimerisation to the well‐known {Mo2O4}2+ core. A dinuclear anion with coordinated methanol can be isolated as its pyridinium salt, (PyH)2[Mo2O4Cl4(MeOH)2], in two crystalline modifications, either as a triclinic (3) or as an orthorhombic polymorph (4). After prolonged reaction times further assembly of dinuclear fragments takes place and tetranuclear [Mo4O8(OMe)2(MeOH)2Cl4]2– is formed. The products of the analogous reactions with (PyH)[MoOBr4] as the starting material depend largely upon the reaction temperature. Dinuclear (PyH)2[Mo2O4Br4(MeOH)2] (5), which crystallises in an orthorhombic unit cell and whose structure is isotypic to that of 4, is obtained only if the reaction takes place at low temperature (5 °C); under ambient conditions (PyH)2[Mo4O8(OMe)2(MeOH)2Br4] (6) is obtained instead. The tetranuclear anion of 6 consists of a commonly adopted assembly of two {Mo2O4}2+ units. The identity of the products was determined by infrared spectroscopy and X‐ray structure analyses. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)