Ab initio study of low pH vanadium (V)

Abstract

The aqueous chemistry of the low pH vanadium (V) species is complex. These low concentration species of vanadium (V) cannot be studied by conventional experimental methods to obtain the important structural information of vanadium compounds. This project studied three compounds of vanadium (V): VO[subscript 2][superscript +] , H[subscript 3]VO[subscript 4] and H[subscript 2]VO[subscript 4][superscript -] using ab initio computational methods (HF, MP2, B3LYP, CCSD(T) and CPMD). The geometries of hydrated (up to six water molecules) VO[subscript 2][superscript +], H[subscript 3]VO[subscript 4] and H[subscript 2]VO[subscript 4][superscript -] were calculated using the ab initio methods. The effects of hydration on the bond lengths and vibrational frequencies of these compounds were established. The coordination of water molecules weakened the bonds and decreased their corresponding vibrational frequencies. The hydrogen bonded water molecules strengthened the bonds and increased their corresponding vibrational frequencies. The mechanism of the conversion of H[subscript 2]VO[subscript 4][superscript -] to VO[subscript 2][superscript +] was studied. The complete hydration of H[subscript 2]VO[subscript 4][superscript -] increased the coordination number to five and the double protonation of its hydroxo ligands produced the VO[subscript 2][superscript +].