Ab Initio Studies On The Electronic Structure And Electronic Spectra Of [M₆(μ₃-X)₈Y₆]～2-(M=Mo,W;X Or Y=Cl,Br,I)

The cluster complexes with cubic core [M6(μ₃-X₈)Y₆)^2- (M=Mo, W; X or Y=Cl, Br, I) have special fluorescence and luminescent behavior. Excited by UV-via light, [M6(μ₃-X₈)Y₆)^2- (M=Mo, W; X or Y=Cl, Br, I) show strong fluorescence, either in solid state or solution. What's more, the cluster complexes have the unusual long-lived luminescence and higher quantum yields. In this studies, the full optimizations for [M6(μ₃-X₈)Y₆)^2- (M=Mo, W; X or Y=Cl, Br, I) are carried out with HF method. On the basis of optimized geometries, molecular orbitals and excited states of the six ions are calculated with Tamm-Dankoff configuration interaction approximation (TDCI) method and the electronic structures of these cluster complexes are obtained. The electronic absorption spectra and the mechanism of fluorescence of [M6(μ₃-X₈)Y₆)^2-(M=Mo, W; X or Y=Cl, Br, I) are explained very well by our calculation results , which, in some extent, is in favor of the photochemical and photo physical investigation of these cluster complexes with cubic core [M6(μ₃-X₈)Y₆)^2- (M=Mo, W; X or Y=Cl, Br, I). It is showed that the frontier orbitals of [M6(μ₃-X₈)Y₆)^2- (M=Mo, W; X or Y=Cl, Br, I) are heavy metal molybdenum and tungsten centered (the percentage of molybdenum and tungsten in the frontier orbitals is about 80%). Thus, after the six cluster ions absorb photon and singlet state ground state are turned into singlet excited, the spin state of electron in excited energy level can change because of the spin-orbit coupling of heavy metal molybdenum and tungsten, which lead to the conversion of c singlet excited state to triplet excited state. And then, the cluster ions return to singlet ground state by means of radiate transition. This is essential reason why [M6(μ₃-X₈)Y₆)^2-(M=Mo, W; X or Y=Cl, Br, I) have vividfluorescence. In addition, the lower oscillatory energy level both in ground state and in excited state of them is another important reason. For fluorescence the calculated results are in good agreement with the experimental results. Theoretically, the absorption spectra result from a mixture of metal-localized transitions and ligand-to-metal charge-transfer transitions, but the emission spectra result from the interaction of metal-localized transitions and metal-to-ligand charge-transfer transitions.