Two α2-Monozirconium-Substituted Dimeric Silicotungstates: Hydrothermal Synthesis, Structural Characterization and Catalytic Oxidation of Thioethers

A novel di-ZrIV-substituted sandwich-type silicotungstate (NH4)2(TMA)6[Zr2(μ-OH)2(α-HSiW11O39)2]·18H2O (1, TMA = tetramethylammonium) and a previously unknown EDTA bridging mono-ZrIV-substituted silicotungstate dimeric cluster (NH4)2(TMA)6[(Zr2EDTA)(α-HSiW11O39)2]·26H2O (2, EDTA = C10H14N2O8) have been synthesized under mild hydrothermal conditions and characterized by FTIR spectroscopy, elemental analysis, thermogravimetric analysis, single-crystal and powder X-ray diffraction. 1 and 2 contain a centrosymmetric polyoxoanion structures with two [α-SiW11O39]8− units sandwiching a [Zr2(μ-OH)2]6+ cluster and [Zr2EDTA]6+ moiety, respectively. The catalytic activities of 1 and 2 on oxygenation of thioethers by H2O2 were evaluated, showing that both 1 and 2 are excellent catalysts for the catalytic oxidation of thioethers to sulfoxides/sulfones.