Three Polymeric Polyoxometalate Compounds Based on Twisted Poly-Keggin Chains



Three polymeric polyoxometalate (POM) compounds, [PMoVI10MoV2O39](C2N4H4)2[(CH3)4N]3·H2O (1), [PW11CuO39]2·[Cu(en)2H2O]4·[(CH3)4N]2·6H2O (en = ethenediamine) (2), and [SiW11CuO39]2·[Cu(en)2]4·[Cu(en)2H2O]2·10H2O (3) were isolated under hydrothermal conditions. Compound 1 contains one-dimensional twisted poly-Keggin chains that consist of two-electron-reduced Keggin units through MoV–Ot–MoV bridges. Compounds 2 and 3 contain one-dimensional twisted poly-Keggin chains that consist of Cu-monosubstituted Keggin units through W–Ot–Cu bridges. Twisted chains are formed due to the different orientations of the Keggin units during polymerization. The compounds were characterized by single-crystal X-ray diffraction, elemental analysis, IR, X-ray photoelectron spectroscopy (XPS), thermogravimetry (TG), and cyclic voltammetry. The driving force for polymerization by the sharing of a terminal oxygen atom per POM unit likely arises from the existence of a low-valence metal (MoV or CuII), which reduces the charge density of each POM unit.