Syntheses and structural determination of new bis(9-tungstoarsenato)tris(dioxouranate(VI)) and its monooxovanadate(IV) derivative complexes

The As₂W₁₈U₃O₇₄]¹²⁻ complex is formed by the “self-assembly” reaction of and (uranyl nitrate) ions in acidic media. The anion complex is isolated as the potassium salt and characterized by elemental analysis, IR, UV-Vis, and X-ray single crystal analysis. The complex contains an anion in which three ions are unsymmetrically sandwiched between two A-α-AsW₉O₃₄]⁹⁻ groups leading to a structure of C_3v symmetry. Each uranium atom adopts pentagonal-bipyramidal coordination, achieved by three equatorial bonds to one AsW₉O₃₄]⁹⁻and two bonds to the other. The As₂W₁₈U₂V₂O₇₃]¹²⁻and also As₂W₁₈U₃O₇₄]¹²⁻ complexes are formed also, by reaction of the KAs₂W₁₈U₂O₇₂]¹³⁻ with VO²⁺ and ions in 1:1 mole ratio. The cyclic voltammogram of As₂W₁₈U₂VO₇₃]¹²⁻ in acetate buffer (pH 4.7) shows a reversible one-electron redox process for V^IV/V couple at +0.396 (E_pc) and +0.432 V (E_pa).