Stability and Structure in - and -Keggin Heteropo

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• 作者：Wade A. Neiwert ; Jennifer J. Cowan ; Kenneth I. Hardcastle ; Craig L. Hill ; and Ira A. Weinstock
• 刊名：Inorganic Chemistry
• 出版年：2002
• 出版时间：December 30, 2002
• 年：2002
• 卷：41
• 期：26
• 页码：6950 - 6952
• 全文大小：70K
• 年卷期：v.41,no.26(December 30, 2002)
• ISSN：1520-510X

文摘

-[SiW₁₂O₄₀]^4- (C_3v symmetry) is sufficiently higher in energy thanits -isomer analogue that effectively complete conversion to-[SiW₁₂O₄₀]^4- (T_d) is observed. By contrast, - and -[AlW₁₂O₄₀]^5-(- and -1; C_3v and T_d, respectively) are sufficiently close inenergy that both isomers are readily seen in ²⁷Al NMR spectra ofequilibrated (-) mixtures. Recently published DFT calculationsascribe the stability of -1 to an electronic effect of the large,electron-donating [AlO₄]^5- (T_d) moiety encapsulated within thepolarizable, fixed-diameter -W₁₂O₃₆ (C_3v) shell. Hence, no uniquestructural distortion of -1 is needed or invoked to explain itsunprecedented stability. The results of these DFT calculations areconfirmed by detailed comparison of the X-ray crystal structure of-1 (-Cs_4.5K_0.5[Al^IIIW₁₂O₄₀]·7.5H₂O; orthorhombic, space groupPmc2₁, a = 16.0441(10) Å, b = 13.2270(8) Å, c = 20.5919(13)Å, Z = 4 (T = 100(2) K)) with previously reported structures of-1, - and -[SiW₁₂O₄₀]^4-, and ₁-[SiMoW₁₁O₄₀]^4-.