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.