On the Origin of the Inverted Stability Order of the Reverse-Keggin [(MnO4)(CH3)12Sb12O24]6−: A DFT Study of α, β,

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• 作者：Fu-Qiang Zhang ; Wei Guan ; Yin-Tang Zhang ; Mao-Tian Xu ; Jian Li ; Zhong-Min Su
• 刊名：Inorganic Chemistry
• 出版年：2010
• 出版时间：June 21, 2010
• 年：2010
• 卷：49
• 期：12
• 页码：5472-5481
• 全文大小：1087K
• 年卷期：v.49,no.12(June 21, 2010)
• ISSN：1520-510X

文摘

Density functional theory calculations have been carried out to investigate the α, β, γ, δ, and ε isomers of [(MnO₄)Me₁₂Sb₁₂O₂₄]⁶⁻ (Me = CH₃) anions, which are simplified Baker−Figgis models of Keggin-type antimonate complexes in experiments. It is found that the stability order of the five isomers (α < β < γ < δ < ε) perfectly reverses to the well-known trend of the classical Keggin [PW₁₂O₄₀]³⁻ anions (α > β > γ > δ > ε), despite their significant similarities in frameworks. On the basis of the building block decomposition method, the stabilizing effect of the edge-sharing [Sb₂(μ-O)₂Me₂] fragment inside γ, δ, and ε structures is confirmed and found to originate from its two energy-favorable components rather than itself as an indivisible unit. Similar behavior is also held by the destabilizing [W₂(μ-O)₂O₂] fragment in [PW₁₂O₄₀]³⁻; however, the well-accepted electrostatic repulsion between the short W^VI−W^VI contacts cannot be taken as direct evidence. Notably, in the assembly of the [(MnO₄)Me₁₂Sb₁₂O₂₄]⁶⁻ structure, all of the octahedral building units incline to compress axially and elongate horizontally, and this is exactly opposite to the deformation pattern observed in the building blocks of Keggin tungstates, which tend to elongate axially and compress horizontally, thus giving rise to the inverted stability order. Furthermore, energy decomposition analysis reveals that the intrinsic property of the anion comes from the spatial arrangements of the metal−oxygen cage and does not change significantly with the type and charge of the encapsulated anion.