Trimethylacetate-bridged mixed-valence binuclear vanadium(IV,V) complexes with a {(VO)2(μ-O)}3+ core

Abstract

The reaction of an oxidovanadium(IV) salt with an N-donor ligand (2,2′-bipyridine (bpy) or 4,4′-di-tert-butyl-2,2′-bipyridine (dtb-bpy)) and M(piv) (M = Li, K, NBu4; piv = (CH3)3CCO2−) in a ratio of 1:1:2 affords complexes [(VO)2(µ-OH)(µ-piv)2(bpy)2](otf) (1), [(VO)2(µ-O)(µ-piv)2(dtb-bpy)2](otf)·H2O (2), or [(VO)2(µ-O)(µ-piv)2(bpy)2](NO3)·Hpiv·H2O (3), respectively (piv = (CH3)3CCO2−, otf = CF3SO3−). According to single-crystal X-ray diffraction, the complexes contain two vanadium atoms bridged by two carboxylate groups and one hydroxo (1) or oxo (2, 3) group. Cyclic voltammetry revealed that both vanadium atoms in 1 have oxidation state +4, whereas one of the two metal atoms in 2 and 3 has oxidation state +4 and another one has +5. The room-temperature EPR spectrum of complex 2 in solution is indicative of delocalization of an unpaired electron between two equivalent metal atoms. In frozen glass (77 K) the electron is localized on one center.