Synthesis, structure and electrochemical characterization of an isopolytungstate (W4O16) held by MnII anchors within a superlacunary crown heteropolyanion {P8W48}

Abstract

An isopolyanion {W₄O₁₆} within an archetypal {P₈W₄₈} heteropolyanion assembly [(P₈W₄₈O₁₈₄)(W₄O₁₆)K₁₀Li₄Mn₁₀Na(H₂O)₅₀Cl₂]¹⁵⁻ (Mn₁₀W₄-P₈W₄₈) has been synthesized by the reaction of the cyclic superlacunary anion [H₇P₈W₄₈O₁₈₄]³³⁻ and Mn(ClO₄)₂·6H₂O in 1 M LiCl solution medium at pH 8. The isolated compound has been characterized by single-crystal X-ray crystallography, powder X-ray diffraction (PXRD), Fourier-transform infrared (FTIR) spectroscopy, elemental analysis and thermogravimetric analysis. Electrochemical studies were also performed on Mn₁₀W₄-P₈W₄₈, which confirmed the presence of Mn centres bonded to the tungstic framework. The novel polyanion [(P₈W₄₈O₁₈₄)(W₄O₁₆)K₁₀Li₄Mn₁₀Na(H₂O)₅₀Cl₂]¹⁵⁻ is the first example of a macrocyclic complex, where an isopolyanion (W₄O₁₆)⁸⁻ is embedded within the inner cavity of {P₈W₄₈} and is placed in position by six Mn^II cations as anchors, whereas the exocyclic coordination of four further Mn^II cations to {P₈W₄₈} yields an extended structure by linking neighbouring polyanions through {W–O–Mn–O–W} bridges. Furthermore, the polyanion Mn₁₀W₄-P₈W₄₈ is the first derivative of {P₈W₄₈} with six Mn^II ions (largest) coordinated to the inner side of the crown ring as anchors.