51V and 17O NMR studies of the mixed metal polyanions in aqueous V—Mo solutions

Abstract

NaVO 3Na 2MoO 4 solutions acidified with HCl were studied at the atomic V/Mo ratios equal to 3 : 1, 1 : 1, 1 : 3, 1 : 6 and vanadium concentration [V] = 0.1, 0.04, 0.004 and 0.0004 M in the range pH 7-2. Their 51V NMR spectra (measured at H ito = 7 T) were compared with those of VW solutions containing mixed metal complexes of known composition. The VMo 5O 19 3− ( 51V NMR chemical shift relative to VOCl 3, δ, −502 ppm), V 2Mo 4O 19 4− (δ −494), V 2Mo 4O 19 3− δ −507), V 9MoO 28 5− (δ −422, −492, −501, −512, −521.5) and HV 9MoO 28 4− polyanions (p.a.) have been found to be dominant mixed species in Na-V-Mo solutions. Along with them the V itxMO 13-itxO −itx−3 40 p.a.( x∼2–3) of the Keggin type (δ −496, −498, −516, −522) are supposed to be formed at pH < 4 in concentrated solutions ([V] > 0.01 M). The V 2Mo 6O 26 6− p.a., isolated at pH ∼ 5 as the sodium salt (solid state δ −482), seem to be present in concentrated Na-V-Mo solutions only as minor species. On dissolving the salt the V 2Mo 6O 26 6− p.a. mainly disproportionates into the complexes mentioned. From solutions containing mainly the V 9MoO 28 5− p.a. the sodium salt of V 10O 28 6− is crystallized. The V 9WO 28 6− p.a. are detected in VW solutions at V/W > 1. 17O and 95Mo NMR spectra of some mixed complexes are described. The distribution diagrams for VMo and V-W solutions at [V] = 0.004 M and V/Mo(W) = 1:3, derived from their 51V NMR spectra, are given.