Oxygen and vanadium exchange processes in linear vanadate oligomers
Abstract
The existence of the linear tri- and tetra-vanadate anions in aqueous solution has been confirmed by 51V and 17O NMR and potentiometry, yielding the formation constants. Their resonances are mostly broadened by an exchange process which is shown by the linewidths and by magnetisation-transfer experiments to be independent of the monomeric or the dimeric vanadates also present, and also of the solvent oxygens. The broadenings are not consistent with a simple process of exchange, but instead reveal the presence of an intermediate, probably cyclic, having a short but not insignificant lifetime. Also, simple proton transfer between the oxygens in the aqueous monoprotonated monovanadate anion is sufficiently slow to be detectable by NMR spectroscopy.