Organic Cation-Regulated Citrate-Modified Monomeric Zirconium-Incorporated Polyoxotungstates: Structural Diversity and Catalytic Oxidation of Sulfides

Abstract

The regulatory effects of organic cations on the structural features and functional performances of polyanions are of paramount significance, which is accompanied by substantial challenges as well as promising opportunities. Herein, we report two monomeric zirconium-substituted phosphotungstates functionalized by citrate ligands: [N(CH3)4]9[Zr(HCIT)(α2-P2W17O61)]·17.5H2O (1) and [H2N(CH3)2]8[Zr(H2CIT)(H2O)2(α2-P2W17O61)]·12H2O (2) (H4CIT = citric acid). These two compounds were obtained via self-assembly of [α-P2W15O56]12–, with dimethylamine hydrochloride and tetramethylammonium chloride selected as control variables to modulate the crystallization process. Significantly, the coordination environments of zirconium ions and the coordination modes of citrate ligands are distinct between compounds 1 and 2. The catalytic oxidation performance of compounds 1 and 2 toward sulfides was systematically evaluated. It is noteworthy that compound 1 exhibits significant catalytic activity in the oxidation of sulfides. This study not only enriches the structural diversity of zirconium-based POMs but also elucidates the critical role of organic cations in modulating the functionalities of polyoxometalates materials.