The syntheses of a series of polyoxoniobate-based compounds: Their characterizations and catalytic applications in styrene epoxidation

Four polyoxoniobate-based compounds, namely [Cu(en)2]4[Cu(en)2(H2O)][VNb12V4O44]·2.25H2O·3OH– (1), [Cu(en)2]4[Cu(en)2(H2O)]3[Cu(en)2(H2O)2]3{[SiNb12Sb2O40]2}·25H2O (2), [Cu(en)2]2[Cu(en)2(H2O)2]4[SiNb12V2O42]·7H2O (3), and [Cu(en)2]3{[Cu(en)2][H2V4Nb6O30]}·12H2O (4) have been successfully synthesized and characterized by using FT-IR, XRD, and single crystal X-ray diffraction analyses, etc. Out of the four compounds, compound 1 is based on a rare four V capped polyoxoniobate cluster [VNb12V4O44]7−, [Cu(en)2]2+, and [Cu(en)2(H2O)]2+ complexes, forming a 1-D chain structure with Cu complexes as bridges. Compound 2 contains a Keggin polyoxoniobate with double Sb caps, and forming a network structure based on Sb capped polyoxoniobates and copper complexes with two different large parallelogram channels. Compounds 3 and 4 have been reported previously by Wang et al[1] and Hu et al[2], respectively. In this work, we not only reported the syntheses, structures and characterizations of these compounds, but also we further investigated the catalytic properties of these four compounds for styrene epoxidation.