New sulfate-bridged dinuclear oxidovanadium complexes

The reaction of oxidovanadium sulfate VOSO4·3H2O with 4,4′-di-tert-butyl-2,2′-bipyridine (dtb-bpy) in methanol was found to give the complex (VO)2(μ2-SO4)2(dtb-bpy)2(CH3OH)2·4CH3OH (1). Single crystal X-ray diffraction reveals that molecule 1 is a centrosymmetric dimer consisting of two {VO(μ2-SO4)(dtb-bpy)(CH3OH)} moieties linked by two bridging sulfate anions. Each vanadium atom is in a distorted octahedral environment formed by two nitrogen and four oxygen atoms. The further reaction of an ethanolic solution of compound 1 with sodium pivalate in CH3CN produces the new dinuclear complex [(VO)2(μ2-O)2(μ2-SO4)(dtb-bpy)2]·2CH3CN (2), which does not include pivalate ligands, but contains one bridging sulfate anion and two bridging oxygen atoms. The X-ray study, cyclic voltammetry and magnetic measurements were performed allowing to conclude that both vanadium centers in 2 are in +5 oxidation state. According to ESR studies the dinuclear complex 1 undergoes dissociation upon dissolution in ethanol yielding mononuclear species VO(μ2-SO4)(dtb-bpy)(CH3OH), while solution of 1 in dichloromethane contains “dimers” exhibiting spin–spin exchange interactions between two paramagnetic monomeric fragments.