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

Abstract

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.