Synthesis, Crystal Structure And Characterization Of Polyoxotungstates Containing Transition Metal Complexes

In this paper, four unreported organic-inorganic hybrid compounds have been synthesized by utilizing a flexible ligand , 3-aminopyrazine-2-carboxylic, an organic chelating ligand, 2, 2'-bipyridyl-3, 3'-dicarboxylic acid, or a bridging ligand, 4,4-bipy, as organic composition, polyoxoanions as inorganic architectures and adjusting reaction conditions and reaction materials. These compounds have been structurally characterized by elemental analyses, UV,IR, DTA,TGA,XPS and single crystal X-ray diffractions.1. A novel organic-inorganic hybrids has been hydrothermally synthesized by using saturated Wells-Dawson tungstoarsenate polyoxoanion, copper(II) acetate and mixed ligands (rigid and flexible). {[CuI3(4,4'-bipy)3]2[CuII(en)2]4[As2W3VW15VIO62]2}[Cu3I(4,4'-bipy)3(H2O)2](H3O)·4H2O (en = ethylenediamine,4,4'-bipy = 4,4'-bipyriline) (1)Compound 1 is the first organic-inorganic hybrid with 3D structure built from saturated Wells-Dawson tungstoarsenate polyoxoanion and transition metal complexes with mixed ligands (rigid and flexible) via covalent linkage. It is difficult to synthesize high-dimensional structure based on Well-Dawson polyoxoanions which have large size and low surface electron density. In order to increase surface charge density, reductive Et3N was added. Contrast to oxidative Wells-Dawson tungstoarsenate polyoxoanion, reduced Wells-Dawson tungstoarsenate polyoxoanion has more negative charges which facilitate their coordination to metal cations and should be an excellent precursor for constructing the materials with high-dimensional structure.2. Three supramolecular compounds containing transition metal are synthesized hydrothermally. CoII4(apza)8(SiW12O40)2·14H2O (apza =3-aminopyrazine-2-carboxylic) (2) CoII4(H2bpdc)4·4H2O (H2bpdc =2, 2'-bipyridyl-3, 3'-dicarboxylic acid) (3) (H2Pz)3[Cr(OH)6Mo6O18](SO4)(HSO4)·12H2O (Pz = Piperazine) (4)Compound 2 shows 3D a supramolecular architecture assembled by transition metal complex and the Keggin polyoxoanion through the hydrogen bonding interactions between them. In compound 3, one-dimensional Z-chain was constructed by ligand 2, 2'-bipyridyl-3, 3'-dicarboxylic acid and cobalt ions. The one-dimensional Z-chains fuse into 3D architecture by hydrogen bonding interactions. Compound 4 is a 3D structure built from polyanion, sulfate ion, water molecules through hydrogen bonding interactions.