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

The reaction of an oxidovanadium(IV) salt with an N-donor ligand (2,2'-bipyridine (bpy) or 4,4'-ditert-butyl-2,2'-bipyridine (dtb-bpy)) and M(piv) (M = Li, K, NBu4; piv = (CH3)(3)CCO2-) in a ratio of 1:1:2 affords complexes [(VO)(2)(mu-OH)(mu-piv)(2)(bpy)(2)](otf) (1), [(VO)(2)(mu-O)(mu-piv)(2)(drb-bpy)(2)](orf)center dot H2O (2), or [(VO)(2)(mu-O)(mu-piv)(2)(bpy)(2)](NO3)center dot Hpiv center dot H2O (3), respectively (piv = (CH3)(3)CCO2-, 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. (C) 2019 Elsevier Ltd. All rights reserved.