Hydrothermal synthesis, structure, and catalytic properties of a (4,6)-connected framework constructed from Keggin-type polyoxometalate units and tetranuclear copper complexes

Abstract

Under hydrothermal condition, a new Keggin-type polyoxometalate(POM)-based metal-organic complex, namely H₄{[Cu₄(EDDP)₂(H₂O)₅]_1.5(SiW₁₂O₄₀)}∙7.5H₂O (<strong>CuW-EDDP</strong>, H₄EDDP = ethylenediamine-N,N'-dipropionic acid) was synthesized by reaction of Na₁₀[A-<em>α</em>-SiW₉O₃₄]·18H₂O and CuCl₂·2H₂O in the presence of H₄EDDP ligand and characterized by X-ray diffraction (powder, single-crystal), Infrared radiation (IR) spectra, elemental analysis, and thermogravimetry. Interestingly, <strong>CuW-EDDP</strong> features a three-dimensional structure with (4,6)-connected built up from [SiW₁₂O₄₀]^4- units and tetranuclear-copper complexes [Cu₄(EDDP)₂(H₂O)₅].<strong> CuW-EDDP</strong> as an effective heterogeneous catalyst exhibited excellent performance, good reusability and structural stability in the selective oxidation of methyl phenyl sulfide (MPS) with high conversion (100%) and selectivity (98%) within 30 min. Furthermore, the catalytic activity of <strong>CuW-EDDP</strong> toward the oxidation of other sulfide derivatives was also investigated.