An unsymmetrical mixed-valent divanadium(IV/V) complex

Abstract

In acetonitrile medium, reaction of bisacetylacetonatooxovanadium(IV) {[VO(acac)2]} and acetylhydrazine (CH3CONHNH2) in a 2:1 molar ratio provides a novel, unsymmetrical, chiral, mixed-valent, triply bridged, dinuclear vanadium(IV/V) complex having the formula [(Hdmpz)OV(μ-acac)(μ-O)(μ-O2CCH3)VO(acac)] (Hdmpz = 3,5-dimethylpyrazole). The molecular structure of the complex was confirmed by X-ray crystallography. It crystallizes in the chiral space group P2 12121 indicating a spontaneous resolution in the crystal. The complex is one-electron paramagnetic and redox active. It displays VVVIV to VVVV oxidation and VVVIV to VIVVIV reduction responses. The crystal structure and EPR measurements revealed the trapped-valent character of the complex in the solid state as well as in the solution phase. Circular dichroism spectroscopic measurements with a powdered sample revealed that the bulk material is not racemic. In solution, the existence of both enantiomers of the complex is demonstrated by the Pfeiffer effect with the use of L- and D-arabinose as environment substances. © Wiley-VCH Verlag GmbH & Co. KGaA, 2009.