Both Rigid Organic Ligands and pH-Controlled Three Keggin-Type Polyoxotungstates Derivates: Synthesis, Crystal Structure

Abstract

Three Keggin polyoxotungstate inorganic–organic hybrid compounds have been synthesized under hydrothermal conditions by using H4SiW12O40 as starting materials: [{CuII(2,2′-bipy)2}2SiW12O40]·2H2O (1), [{CuII(phen)2}2SiW12O40] (2) and [{CuI(2,2′-bipy)2}4SiW12O40] (3) (2,2′-bipy\u2009=\u20092,2′-bipyridine, phen\u2009=\u20091,10′-phenanthroline) and structurally characterized by elemental analysis, IR spectra, TG analysis and X-ray single-crystal diffraction. Three compounds are all based on [SiW12O40]4− α-Keggin type building block and synthesized under the same reaction condition, only different compound 1 and 2 ligand, 1 and 3 pH value. Compound 1 displays a novel example of two-dimensional framework with tetra-supporting α-Keggin polyanions which are linked by four same fragments and it becomes 3D structure due to the existence of hydrogen bonds. Compound 2 shows that the bi-supporting polyoxotungstate molecule consists of a α-Keggin polyoxoanion [SiW12O40]4− and a pair of transition metal complex fragments which are covalently linked to opposite sides of the surface terminal oxygen atoms of WO6 octahedra. Compound 3 consists of α-[SiW12O40]4− polyoxoanions, counter cations [Cu(2,2′-bipy)2]+. The crystal packing is stabilized by H-bonds and weak π–π interactions, leads to a 3D supramolecular architecture. The results show that the pH value of the reaction system plays a crucial role in structural control of self-assembled processes. The thermal stabilities of the compounds are discussed. Three Keggin polyoxotungstate inorganic–organic hybrid compounds have been synthesized under hydrothermal conditions by using H4SiW12O40 as starting materials: [{CuII(2,2′-bipy)2}2SiW12O40]·2H2O (1), [{CuII(phen)2}2SiW12O40] (2) and [{CuI(2,2′-bipy)2}4SiW12O40] (3) (2,2′-bipy\u2009=\u20092,2′-bipyridine, phen\u2009=\u20091,10′-phenanthroline) and structurally characterized by elemental analysis, IR spectra, TG analysis and X-ray single-crystal diffraction. Three compounds are all based on [SiW12O40]4− α-Keggin type building block and synthesized under the same reaction condition, only different compound 1 and 2 ligand, 1 and 3 pH value.