Synthesis and Spectroscopic Characterization of Two New Dawson Sandwich Complexes: Na₁₈[(NaOH)₂(VO)₂(P₂W₁₅O₅₆)₂].40H₂O and Na₁₈[(NaOH)₂(VO)₂(As₂W₁₅O₅₆)₂].27H₂O

Abstract

Reaction of the three vacant complex of a-[P₂W₁₅O₅₆]^12- and a-[As₂W₁₅O₅₆]^12- with divalent cation of VO²⁺ in 1:1 mole ratio yields a previously unknown sandwich-type Wells-Dawson complex; Na₁₈[(NaOH)₂(VO)₂(P₂W₁₅O₅₆)₂].40H₂O (represented as Na₂(VO)₂P₄W₃₀) and Na₁₈[(NaOH)₂(VO)₂(As₂W₁₅O₅₆)₂].27H₂O (represented as Na₂(VO)₂As₄W₃₀). These complexes contain anions in which two divalent VO²⁺ cations with two Na⁺ ions are symmetrically sandwiched between two α-[P₂W₁₅O₅₆]12- or α-[As₂W₁₅O₅₆]^12- groups leading to a “lacunary” sandwich complex. The anion complexes are isolated as sodium salts and characterized by elemental analysis, TGA, IR, 31P NMR and UV-Vis spectroscopy.