Abstract
In acetonitrile medium, reaction of bisacetylacetonatooxovanadium(IV) {[VO(acac)~2~]} and acetylhydrazine (CH~3~CONHNH~2~) 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‐O~2~CCH~3~)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 __P__2~1~2~1~2~1~ indicating a spontaneous resolution in the crystal. The complex is one‐electron paramagnetic and redox active. It displays V^V^V^IV^ to V^V^V^V^ oxidation and V^V^V^IV^ to V^IV^V^IV^ 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, 69451 Weinheim, Germany, 2009)