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Inversed Stability Order in Keggin Polyoxothiometalate Isomers:  A DFT Study of 12-Electron Reduced α, β, γ, δ, and ε [(MoO4)Mo12O12S12(OH)12]2- Anions

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posted on 08.03.2007, 00:00 by Fu-Qiang Zhang, Xian-Ming Zhang, Hai-Shun Wu, Yong-Wang Li, Haijun Jiao
Density functional theory calculations have been carried out to investigate 12-electron reduced α, β, γ, δ, and ε Keggin-like [(MoO4)Mo12O12S12(OH)12]2- polyoxothiometalates (POTMs), which show that the stability order is α < β < γ < δ < ε that is perfectly inverse to the well-known trend of the classical Keggin polyoxometalates. Energy decomposition analysis reveals that the enhanced stabilities of γ, δ, and ε isomers originate the favorable arrangements of their Mo12O12S12(OH)12 shell, in which the edge-sharing [MoV2(μ-S)2O2] fragment plays a fundamental role in stabilizing the overall structure. Both frontier orbital analysis and Mayer indexes exhibit that a Mo−Mo single bond is formed inside the [MoV2(μ-S)2O2] fragment, which leads to the localization of the two reduced electrons. As compared with experimentally discovered cyclic [(C9H3O6)@Mo12O12S12(OH)12]3-, all Keggin POTM structures are less stable due to their disfavored cage framework and the disadvantageous host−guest interaction. However, the ε-type Keggin POTM that has the largest similarity to the cyclic species is possibly available in the presence of appropriate templates.

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