Two inorganic-organic hybrids based on a polyoxometalate: Structures, characterizations, and epoxidation of olefins

Two new inorganic-organic hybrids, [Co-3(bpdo)(6)(H2O)(4)Cl-2][SiW12O40]H2O (Co-SiW) and [Ni-3(bpdo)(6)(H2O)(4)Cl-2][SiW12O40]H2O (Ni-SiW) (bpdo=4,4-bis(pyridine-N-oxide)), were synthesized from the Keggin-type [SiW12O40] anion and Co(II) and Ni(II) under hydrothermal conditions, respectively, and characterized by elemental analyses, powder XRD, IR spectra, and single-crystal X-ray diffraction. The structural analysis indicates that the 1D chain is constructed from a POM-based half-cage as a secondary building block linked by bridging bpdo ligands. The zigzag chains further stack into a three-dimensional body with channels. The 3D network structure with amphiphilic cavities is shaped by electrostatic interactions through the planes, which has potential to allow molecules such as styrene and H2O2 ingress and egress. Both of the hybrids demonstrated catalytic activity for epoxidation of olefins, which was examined using styrene and aqueous hydrogen peroxide (30%) as oxidant in acetonitrile, along with Co-SiW and Ni-SiW in a heterogeneous manner at 60 degrees C. Moreover, the conversion of epoxidation reaction in a heterogeneous manner is close to that of homogeneous catalysis, while being conveniently recovered and steadily reused without change of catalyst structure after epoxidation reactions. [GRAPHICS] .