Three ring-shaped Zr(iv)-substituted silicotungstates: Syntheses, structures and their properties

Three Zr(iv)-substituted polyoxometalate nanoclusters, H16(H2dap)4[{Zr2(OH)2(α-SiW10O38)}2{Zr2(OH)2(β-SiW10O38)}2]·8H2O (1, dap = 1,3-diaminopropane), H17Na9[(Zr2(OH)2)2(Zr2BO(OH)4)2(β-SiW10O38)4]·50H2O (2) and H20Na8[(Zr2BO(OH)4)2(Zr2B2O2(OH)5)2(β-SiW10O38)4]·40H2O (3), were made by a hydrothermal reaction of trivacant [A-α-SiW9O34]10-, Zr4+ ions, and H3BO3 under different alkaline conditions. Single-crystal X-ray structure analysis revealed that they are ring-shaped polyoxotungstate aggregates built by Zr2(OH)2 ({Zr2}) clusters and two types of dilacunary α-/β-SiW10O38 ({α-/β-SiW10}) fragments for 1, {Zr2}, {β-SiW10}, and Zr2BO(OH)4 ({Zr2B}) clusters for 2, and {β-SiW10}, {Zr2B}, and Zr2B2O2(OH)5 ({Zr2B2}) clusters for 3, respectively, showing that the Zr-B-O clusters, {Zr2B} and {Zr2B2}, have been introduced to the lacunary sites of polyoxometalates for the first time. The electrochemistry and electrocatalytic properties of 2 were studied, and it exhibited effective catalytic activities for the reduction of H2O2, NO2-, and BrO3-. Moreover, the catalysis of 2 for the oxidation reactions of various thioethers was investigated, and it was found that 2 possessed high conversion and remarkable selectivity.