Zr4-Substituted polyoxometalate dimers decorated by d-tartaric acid/glycolic acid: syntheses, structures and optical/electrochemical properties

Abstract

In this article, two new tetra-Zr(IV)-substituted sandwich-type Keggin polyoxometalates functionalized by chiral D-tartaric acid and glycolic acid, K₂H₁₀[Zr₄(H₂O)₂(μ-OH)(μ₃-O)₂(D-tartH)(GeW₁₀O₃₇)₂]·27H₂O (1, D-tartH₄ = D-tartaric acid) and K₂H₁₀[Zr₄(H₂O)₂(μ₃-O)₂(gly)₂(GeW₁₀O₃₇)₂]·32H₂O (2, glyH₂ = glycolic acid), have been synthesized under hydrothermal conditions and characterized by FT-IR spectra, elemental analysis, single-crystal X-ray structure analysis, powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA), ultraviolet-visible absorption spectroscopy (UV-vis) and cyclic voltammetry (CV). The structure analysis reveals that both 1 and 2 contain a [Zr₄(H₂O)₂(μ₃-O)₂(GeW₁₀O₃₇)₂] cluster. UV-vis spectra indicate that both compounds are a wide-gap semiconductor. In addition, compound 1 is a chiral Zr(IV)-substituted sandwich-type Keggin cluster because the D-tartH ligand is chiral and the Flack divisor of 1 is 0.00, showing non-linear optical properties. The cyclic voltammograms indicate that compounds 1 and 2 have good electrocatalytic activity in the reduction of H₂O₂.