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 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.

Keywords

• polyoxometalates
• keggin-type
• metal–organic complex
• catalytic oxidation
• sulfides