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

Under hydrothermal conditions, a Keggin-type polyoxometalate-based metal–organic complex, H₄{[Cu₄(EDDP)₂(H₂O)₅]_1.5(SiW₁₂O₄₀)}∙7.5H₂O (CuW-EDDP, H₄EDDP = ethylene-diamine-N,N'-dipropionic acid), was synthesized by reacting Na₁₀[A-α-SiW₉O₃₄]·18H₂O and CuCl₂·2H₂O in the presence of H₄EDDP ligands and characterized by powder and single-crystal X-ray diffraction, infrared spectroscopy, elemental analysis, and thermogravimetry. Interestingly, CuW-EDDP exhibited a three-dimensional structure with (4,6)-connected constructed from [SiW₁₂O₄₀]⁴⁻ units and tetranuclear Cu complexes [Cu₄(EDDP)₂(H₂O)₅]. As an effective heterogeneous catalyst, CuW-EDDP exhibited excellent performance, good reusability, and structural stability in the selective oxidation of methyl phenyl sulfide with high conversion (100%) and selectivity (98%) within 30 min. Furthermore, the catalytic activity of CuW-EDDP in the oxidation of other sulfide derivatives was investigated.