Two 3D Two-Fold Interpenetrated Dia-Like Polyoxometalate-Based Metal–Organic Frameworks: Synthesis and Sulfide Selective Oxidation Activity

Two new three-dimensional (3D) polyoxometalate-based metal-organic frameworks (POMOFs), [M₂(btap)₄(H₂O)₄(HPMo₁₀^VI Mo₂^VO₄₀)] (M = Co (1) and Cd (2); btap = 3, 5-bis(1', 2', 4'-triazol-1'-yl)pyridine), have been synthesized under mild hydrothermal conditions and characterized in detail. Single-crystal X-ray diffraction (SXRD) analysis indicates that 1 and 2 are isostructural. In complexes 1 and 2, the metal ion is coordinated with the ligand to form two different left and right helical one-dimensional chains, which are alternately connected in a twisted form to build a two-fold interpenetrated three-dimensional structure, and the polyoxometalate is encapsulated into in the pores generated by the interpenetrating structure. It is noteworthy that 1 and 2, as recyclable catalysts, possess favorable heterogeneous catalytic activity and excellent sulfoxide selectivity in sulfide oxidation reactions, with H₂O₂ as an oxidant. By reason of the high dispersion of polyoxometalate with good intrinsic activity in the skeleton structure, the title complex has high activity. In addition, no obvious decrease of sulfoxide yield is observed after at least five cycles. These results indicate the excellent catalytic activity and sustainability of 1 and 2.