Vanadotungstate isopolyanions with V: W = 4: 2 in aqueous solutions and in crystalline salts

Polycondensation in solutions containing HVO ₄ ^2? and WO ₄ ^2? ions in the 4: 2 ratio and the overall concentration c _v+w ⁰ = 5 × 10^?3 mol/l is studied. Speciation diagrams for individual and mixed vanadium(V) and tungsten(VI) polyanions are plotted based on the results of simulation for pHs 2–13 (Z = 0–3.50) on the nitrate ion background. The 6-isopolyvanadotungstate formed in the solutions retain the initial V: W ratio. The concentration formation constants for the vanadotungstate isopolyanions in aqueous solutions are determined. Compounds Tl₆V₄W₂O₁₉ · 5H₂O, Pr₂V₄W₂O₁₉ · 14H₂O, and Na₅HV₄W₂O₁₈ · 27H₂O are synthesized. Their formulas are identified using chemical analysis and IR spectroscopy.