Bromoaquo-complexes of vanadium(III)

Abstract

Vanadium(V) oxide is reduced to bromovanadium(III) species in aqueous hydrogen bromide. Green crystals [of general formulae M₂VBr₅(H₂O)₅(M = Rb⁺, Cs⁺, pyH⁺)] have been isolated from such solutions; these complexes can be successively dehydrated via M₂VBr₅(H₂O)₃ and M₂VBr₅H₂O to M₂VBr₅. The magnetic and spectral properties of these complexes and also of VBr₃(H₂O)₆ are reported, in addition to X-ray powder photographs on the penta-aquocomplexes. From acetic acid solutions of hydrogen bromide, green VBr₃(H₂O)₄ and red Et₄N[VBr₄(MeCO₂H)₂] have been isolated; the latter complex is readily converted into Et₄N[VBr₄(MeCN)₂]. All the complexes are considered to have basically octahedral stereochemistry; the ligand field around vanadium in M₂VBr₅(H₂O)₅, M₂VBr₅(H₂O)₃, VBr₃(H₂O)₆, and VBr₃(H₂O)₄ consists of 4H₂O and 2Br^– as nearest neighbours M₂VBr₅ must contain bridging Br^– ions.