Copper (II) substituted heteropoly molybdate and tungstate of the keggin type anion [Xⁿ⁺M₁₂O₄₀]^−(8-n): Their synthesis and characterization

Two heteropoly oxometalates with molecular formula Na₆[Cu^IIMo^VI₁₂O₄₀].14H₂O(1) and Na₆[Cu^IIW^VI₁₂O₄₀].11H₂O(2) having Keggin type anion [Xⁿ⁺M₁₂O₄₀]^−(8-n) have been synthesized in which the central XO tetrahedra are replaced by CuO₄. The compound^[1] is prepared from aqueous solution of Na₂MoO₄.2H₂O and CuCl₂.2H₂O at pH = 4.5 and the compound^[2] from an aqueous solution of Na₂WO₄.2H₂O and CuCl₂.2H₂O at pH = 4.9. The elemental analyses predict 1:12 atomic ratio of the heteroatom (Cu^II) to the addenda Mo and W respectively. The peaks in the IR studies for both the compound are in good agreement with the proposed formulae. The stretching of Cu-O bands occupy at higher frequencies than that for the Anderson anion which is due to lower coordination number of copper atom. The compounds are further characterized by thermal analyses and molecular weight determination.