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Abstract
Three inorganic–organic hybrid materials based on Keggin-type polyoxometalates (POMs), [CuII2(phen)2(4,4′-bipy)(H4,4′-bipy)2(H2O)2][PMo12O40]2·2H2O (1), [CuII(phen)2(H4,4′bipy)][PW12O40]·H2O (2), and [CuII2(phen)2(4,4′-bipy)(BW12O40)(H2O)2](H24,4′-bipy)0.5·3H2O (3) (phen = 1,10-phenanthroline, 4,4′-bipy = 4,4′-bipyridine), were synthesized using different POMs in the hydrothermal conditions. Compounds 1–3 were characterized by single-crystal X-ray diffraction, IR spectra, elemental analyses, powder X-ray diffraction analyses, and thermogravimetric analyses. Compound 1 presents a two-dimensional (2-D) network containing the Keggin-type [PMo12O40]3− anion and dinuclear metal–organic units [CuII2(phen)2(4,4′-bipy)(H4,4′-bipy)2(H2O)2]3+. Compound 2 is a 2-D architecture constructed from a [PW12O40]3− and mononuclear metal–organic units [CuII(phen)2(H4,4′-bipy)]3+. In 3, the [BW12O40]5− anions link [CuII2(phen)2(4,4′-bipy)] units to form a one-dimensional (1-D) chain [CuII2(phen)2(4,4′-bipy)(BW12O40)(H2O)2]; the 1-D chain connects with protonated 4,4′-bipy ligands and lattice waters, yielding a 2-D layer. Fluorescence spectra, UV–vis spectra, and electrochemical properties of 1–3 have been investigated.
Though PMo12, PW12, and BW12 are all Keggin-type POMs, they exhibit different coordination abilities and electron densities under different pH conditions. Therefore, the types of POMs and pH value have effects on the formation of various frameworks.