Organic–inorganic hybrid materials based on iron(iii)-polyoxotungstates and 1-butyl-3-methylimidazolium cations

Abstract

The iron(III) μ-oxo bridged dimeric polyoxometalate [(PW₁₁O₃₉Fe)₂O]¹⁰⁻ was isolated by reacting the transition metal monosubstituted Keggin anion [PW₁₁O₃₉Fe(H₂O)]⁴⁻ and the ionic liquid 1-butyl-3-methylimidazolium bromide, (Bmim)Br, at pH 5.5. The crystal structure of (Bmim)₁₀[(PW₁₁O₃₉Fe)₂O]·0.5H₂O (1) (monoclinic, space group P2₁/n, Z = 4) was determined by single crystal X-ray diffraction. By changing the reaction conditions, (Bmim)₄[PW₁₁O₃₉Fe(H₂O)]·H₂O (2) was obtained, whilst the reaction between the Bmim⁺ cation and the heteropolyanion [SiW₁₁O₃₉Fe(H₂O]⁵⁻, in the pH conditions used for 1, afforded (Bmim)₅[SiW₁₁O₃₉Fe(H₂O)]·4H₂O (3). The compounds were characterized by spectroscopic techniques, thermal analysis, cyclic voltammetry, magnetic measurements and mass spectrometry. This study contributes to the understanding of iron μ-oxo dimer formation in polyoxometalate chemistry and calls attention to the influence of the counter-cations on the stability and formation of compound 1. The combination of the cationic part of ionic liquids and iron-substituted polyoxotungstates is predicted to lead to new materials with interest to catalysis, electrocatalysis and ionic liquid based nanocomposites.