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

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.