Vanadium-51 and oxygen-17 nuclear magnetic resonance study of vanadate(V) equilibria and kinetics

Abstract

Approximately 15 vanadate(V) and polyvanadate(V) species have been identified by ⁵¹V n.m.r. in the range pH 7–14, mostly for the first time. Oxygen-17 n.m.r. spectroscopy confirms in several cases that the vanadium coordination is tetrahedral, and that the ¹⁷O shifts are correlated closely with formal π-bond order. Most linear and cyclic catenations of VO₄ tetrahedra are found up to V₆, but there is no branched or triprotonated species or cyclic trimer. Several equilibrium constants and pK_a values are reliably measurable. The ion [HVO₄]^2– rather than OH^– is shown to be the dominant nucleophile in the two main ring-breaking reactions, and a simple kinetic pathway is proposed for the formation of decavanadate ion.