A series of Keggin- and Wells-Dawson-polyoxometalate-based compounds constructed from oxygen-functional imidazole derivatives

Through the use of two kinds of imidazole derivatives containing different O-functional units, three new Keggin- and one Wells-Dawson-polyoxometalate (POM)based compounds, namely [Cu2L4a(HPW12O40)] (1), [CuL4a(H2O)(2)(HPMo12O40)] (2), [Cu2L7a(H2O)(H2P2W18O62)]center dot L-a(3), [Ag-2(L-4(b))(HPMo12O40)]center dot L-b center dot H2O (4)(L-a = (4 (2,5 dihydro-1H-imidazol-1-yl)benzaldehyde), and L-b= (4-(2,5-dihydro-1H-imidazol-1-yl)benzoic acid), were synthesized and characterized using single-crystal X-ray diffraction, elemental analyses, and infrared spectroscopy. The polyoxoanions occupy holes framed by two symmetrically oriented CuL2a units in 1. In compound 2, the square-planar CuL4a units form a two-dimensional (2D), supramolecular grid through pi center dot center dot center dot pi stacking interactions. The POMs occupy vacancies in this grid. In compound 3, the CuL3a subunits connect the neighboring P2W18 units and an "S"-type chain is formed. Through hydrogen bonding interactions, the chains are connected to form a layer. In compound 4, the POM anions are linked by AgL2b subunits to form a chain. All the chains are tied together to construct a layer structure with weak hydrogen bonding interactions between the terminal carboxylic acid functional groups of ligands L-b. The electrocatalytic and photocatalytic activities of all these four compounds were also studied.