The Electronic Properties Of Dilacunary Keggin Polyoxometalates [γ-X～(n+)W₁₀O₃₆]～((12-n)-) (X=Al, Si, P, S, Ga, Ge, As, Se) By DFT

Polyoxometalates (POMs) are a class of metal-oxygen clusters, which have shown a variety of applications ranging from catalysis, biology, medicine to analytical chemistry and materials because of their unique structural variety and electronic property diversity. Recently, the electronic property, redox property, bonding character, the stability of the isomers, and the charge transfer of POMs and their derivatives arise much attention.We have investigated the properties of two kinds of POMs using quantum chemistry method in this thesis, one is electronic properties of dilacunaryγ-Keggin POM, and the other is the third NLO properties of hybrids in which the hexamolybdates and transition metal complex are covalentlty bonded. We summarized them below:1. The geometrical structures and the electronic properties of the dilacunaryγ-Keggin [γ-Xn+W10O36](12-n)-(X=Al,Si,P,S,Ga,Ge,As,Se) have been studied by DFT method. The results showed that some geometrical parameters and the energies of HOMO and LUMO of the dilacunaryγ-Keggin POMs are dependent on the X. However, theΔE(HOMO-LUMO) is not. [γ-SiW10O36]8- is a popular precursor for several groups. The decatungstosilicate itself, as well as some of its transition metal derivatives, has shown interesting catalytic properties. Considering the similarity of the electronic properties between [γ-SiW10O36]8- and [γ-GeW10O36]8-, we reasoned that [γ-SiW10O36]8- can be replaced by [γ-GeW10O36]8- as reagent, and we expect that more novel POMs and their derivatives be synthesized.2. The third-order nonlinear optical (NLO) properties of [Fe (4′-(C≡C-C6H3-m-dimethyl)-2, 2′: 6′, 2″-terpyridine) 2]2+ (system 1) and the transition metal complex/hexamolybdate hybrids (M = Fe and Ru, systems 2 and 3, respectively) have been investigated using TDDFT-SOS method. The structures of the studied systems can be viewed as two same fragments perpendicularly joined together through a bridged metal atom. Systems 2 and 3 possess remarkably large third-order nonlinear coefficients, are of a numerical order as large as 10-31esu. We have also made the comparison with the third-order NLO responses of systems 1 and 2. The results reveal that the introduction of hexamolybdate into the transition metal complex can effectively enhance the third-order nonlinearity caused by the increased electron-donor capability of hexamolybdates. The NLO property of the hybrid system with transition metal Ru is remarkably better than that of Fe counterpart.