Phase Transitions in Metavanadates. Polymerization of Tetrakis(<i>tert</i>-Butylammonium)-<i>cyclo</i>-Tetrametavanadate

Abstract

The compound tetrakis(tert-butylammonium)-cyclo-tetrametavanadate(V), the first oxovanadate salt isolated from aqueous solution which contains a discrete unprotonated [V4O12]4- anion, undergoes an irreversible, reconstructive, continuous, and heterogeneous phase transition in the solid state by means of a nucleation and growth mechanism. This transformation yields a polymeric metavanadate of tert-butylammonium and it has been followed by X-ray powder diffraction and FTIR techniques. The polymeric compound has also been isolated from aqueous solution and its crystal structure resolved by single-crystal X-ray diffraction methods, this compound crystallizes in the monoclinic space group P21, a = 10.397(2) Å, b = 5.873(1) Å, c = 13.879(4) Å, β = 111.02(3)°, V = 791.1(3) Å3, Z = 4, and R = 0.026 for 1926 observed reflections with I ≥ 3σ(I). Comparison of the polymeric and cyclic metavanadate structures reveals several structural similarities such as V···V contacts and V−O−V angles. A possible transformation mechanism has been suggested on the basis of these structural analogies.