Design And Construction Of POMs Compounds With Extended Structures

Polyoxoanion is a big family of inorganic anionic cluster composed of early transition metal ions and oxygen atoms. The compounds containing polyoxoanions are called polyoxometalates (POMs) or polyacid. Polyoxoanions show nano-scaled size, big molecular weight and abundant structures with super acidity and excellent multi-electron redox reversibility. POMs have been found versatile applications in many areas, such as catalysis, electrochemistry, material and energy, etc.This thesis focuses on the design and synthesis of POMs-based compounds with extended structures. By introducing structural linkers with positive charge to compensate the charge balance and connect the discrete polyoxoanion building blocks, various POMs-based compounds with extended structures were isolated. We have studied some effects on construction of the extended structures such as, the coordination geometry of cations, the size of ligands, the types of counter ions, redox atmosphere, etc. The metal ions were found to be helpful both in constructing small POMs clusters and 3D rigid frameworks with complex topologies. The investigation of ligands with various length shows that the short ligands led to the formation of structures in closed packing mode while the long ligands could create porous structures by spacing the POMs units. Further studies showed that the POMs units could aggregate into polymeric structures when their terminal oxygen atoms were activated by substitution or chemical reduction. The self- aggregation of the POMs units offers a new method for design and synthesis of POMs-based compounds with extended structures. The rational choice of structural linkers and POMs building blocks, combined with varying interactions between distinct units, leads to formation of extended POMs compounds with diversity in structure, dimension and topology. The design and synthesis of POMs-based compounds with complex structures, diverse compositions and plentiful functions could be achived by using this strategy.In this thesis,22 POMs compounds with extended structures have been isolated under routine or hydrothermal synthesis condition. The structures of the compounds have been solved by single-crystal X-ray diffraction, and their properties have been characterized by IR, elemental analysis, TG, XRD, XPS, CV, etc. The effects of reactants molar ratio, configuration of ligands, reaction temperature, pH and ionic strength on the composition, structure and dimension of the product have been studied. The relationship between structure and property was also preliminarily discussed.The results of the thesis are summarized as follows:1. Compounds 1-2 were isolated by reaction of lacunary polyoxoanion [As2W19O67(H2O)]14- and transition metal ions in aqueous solution under ambient condition. Compound 3 was obtained by further introducing glycine molecules as structural linker: [β-AsW9O33]2[Mn(H3O)2Mn(H2O)3]2Cs2Na4·8H2O (1) [β-AsW9O33]2[Fe(H2O)2Fe(H2O)3]2Cs2Na4·11H2O (2) [β-AsW9O33]2[Fe(H2O)2]2[Fe(H2O)2(C2H5NO2)]2Cs2Na4·9H2O (3)Compounds 1-2 are isostructural constructed by joining two [β-AsW9O33]9- units with four transition metal ions. Compounds 3 also contains the similar polyoxoanion units in 1-2, which is further connected into 1D chains through the hydrogen bonding of glycine molecules that coordinated with the Fe centers. The 3D structures of 1-3 are constructed by the linking of Cs+ and Na+ as counter ions. The oxidation of styrene was chosen as a model reaction and the effects on the catalytic activity of 1-3 were discussed.2. The Cu(2,2’-bpy) moiety was introduced as structural linker to assemble the chiral polyoxoanion [MnMo9O32]6-as building blocks. The organic-inorganic hybrid compounds 4-6 were isolated by using different counter ions during the assembling processes: [MnMo9O32]2Cu(2,2’-bpy)]5Na2·5H2O (4) [MnMo9O32][Cu(2,2’-bpy)(H3O)]2Na·5H2O (5) [MnMo9O32]2[Cu(2,2’-bpy)]5(H3O)2·7H2O (6)In compound 4, the [MnMo9O32]6- with different chirality are connected into 1D double chain by Cu(2,2’-bpy). In compound 5, the [MnMo9O32]6- with different chirality are connected alternatively into 1D chain by Cu(2,2’-bpy) which are further connected into 2D layers by Na+. Compound 6 contains a 3D hydrogen bonding structure constructed by [MnMo9O32]2[Cu(2,2’-bpy)]5 units.Compound 7-8 were isolated by reaction of lanthanide ions, isonicotinic acid and [MnMo9O32]6- in aqueous solution: [(CeMo12O42)Mn][Na(H2O)2]6 (7) [PrMo12O42]4[Pr8(INA)6(H2O)12][Pr(H2O)2]12 (8)The Waugh type polyoxoanion transforms into Silverton type during the isolation of 7-8. Compound 7 is a 3D network connected by [CeMo12O42]8-,Na+ and Mn2+. Compound 8 displays a cubic network connected by [PrMo12O42]8-, Pr3+ and isonicotinic acid molecules. The [PrMo12O42]8- polyoxoanion represents the first example of Silverton type polyoxoanion using Pr3+ as heteroatom.3. Two long N-donor ligands,3,5-di(4-pyridin-4-yl)-4H-1,2,4-triazole (4-bpt) and N,N’-1,4(phenylene) diisonicotinamide (4-bpta) are selected as structural spacers. Compounds 9-16 were isolated under hydrothermal condition by reaction of the Keggin or Dawson type building blocks, transition metal ions and ligands: [SiW12O40][H4(4-bpt)5]·6H20 (9) [SiW12O40][Cu(C6H6N02)2][N(CH3)4]2·4H20 (10) [H6P2W20Fe4O79][H(4-bpt)]5·5H2O (11) [H2P2W18O62][Cu(4-bpt)]4·5H2O (12) [HSiW12O40]2[H2(4-bpta)]3·4H20 (13) [PMo12O40]2[H2(4-bpta)]3·5H2O (14) [P2W18O62][H2(4-bpta)]2[N(CH3)4]2·3H2O (15) [PW12O40]Cu4(4-bpta)4(CH3COO)·6H2O (16)In compounds 9-10, the [SiW11O40]4- polyoxoanions display 3D hydrogen networks constructed by Keggin units and ligands are anchored in the 3D hydrogen networks constructed by ligands or coordination moiety. In compound 11, a dimeric unit is formed by joining two Fe substituted Keggin uints through Fe-O-Fe bonds, which further packs into 3D structure through hydrogen bonds. Compound 12 is a 3D rigid framework constructed by [P2W18O62]6- and Cu(4-bpt) coordination moiety. In compounds 13-14 the Keggin units are anchored in the 3D hydrogen bonding networks constructed by ligands. In compound 15, the [P2W18O62]6- units and 4-bpta molecules are extended into 3D structure through hydrogen bonds. In compound 16, the Keggin units are linked by Cu(4-bpta) moieties into 2D layer with cages inside. The layers are further connected into 3D network through interpenetration. The electrochemical behavior and catalytic activity for reduction of nitrite over compounds 12-16 have been studied.4. Two compounds 17-18 constructed by hydrogen bonding were isolated by assembling the titanium substituted Keggin unit [PTi2W10O40]7- in the existence of morpholine molecules: [H2Pr12W10O40]2[K(C4H10NO)4]2 (17) [H2PTi2W10O40](C4H10NO)5 (18)The 3D structures of compound 17-18 are constructed through hydrogen bonding. Compound 18 shows three 21 screws at a, b, c directions.Compound 19 containing dimeric polyoxoanions were isolated by reaction of hexa-lacunary [H2P2W12O48]12- units and [Nb6O19]8- under the existence of H2O2: [P2W12O59Nb4(NbO2)2]2K4Na8H4·21H2O (19)The dimeric polyoxoanions in compounds 19 are constructed by joining two {P2W12Nb6} units through Nb-O-Nb bonds.5. Three compounds containning polymeric structures were isolated by reaction of Keggin units, copper ions and 1,2-(tetrazol-1-yl)ethane under hydrothermal condition. [PW11CuO39]2[Cu(C2N2H8)2H2O]4[(CH3)4N]2·6H2O (20) [SiW11CuO39]2[Cu(C2N2H8)2]4[Cu(C2N2H8)2H2012·10H2O (21) [PMoⅥ10MoⅤ2O39](C2N4H4)2[(CH3)4N]3·H2O (22)In compounds 20-21, the Cu mono-substituted Keggin units are aggregated into 1D infinite chain through Cu-O-W bonds by sharing terminal oxygen atoms. The 1D polymeric chain in compound 22 is constructed by the reduced [PMoⅥ10MoⅤ2O39]5-Keggin units through oⅤ-Ot-MoⅤ bonds.