The Enhancement of the Formation of Wells-Dawson-Type Polyoxometalates by the Addition of High Concentrations of LiCl

Wells-Dawson-type polyoxometalates are formed by heating an acidic Mo(VI) or W(VI) solution containing significantly higher concentrations of hetero ions, P(V) or As(V), than the ideal molar ratio [M]/[X] = 1/9 (M = Mo, W; X = P, As). Most of the phosphate and arsenate remains unreacted in the reaction mixture. These reaction conditions are unusual, even though more reagents than the stoichiometric amounts are frequently needed to obtain complete reactions. In the present study, the replacement of a large amount of unreacted hetero ions containing salts by normal ions (salts) was investigated. The formation of Wells-Dawson-type polyoxometalates, [X2M18O62](6-) (X = P, As; M = Mo, W), in the presence of LiCl and NaCl was investigated by Raman spectroscopy and P-31 NMR in aqueous solution. The addition of LiCl enhanced the formation of Wells-Dawson-type polyoxometalates, which formed under solution conditions close to the ideal molar ratio [M]/[X] = 1/9.