Effect of Electron (De)localization and Pairing in the Electrochemistry of Polyoxometalates: Study of Wells鈥揇awson Molybdotungstophosphate Derivatives

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• 作者：Lo茂c Parent ; Pablo A. Aparicio ; Pedro de Oliveira ; Anne-Lucie Teillout ; Josep M. Poblet ; Xavier L贸pez ; Isra毛l M. Mbomekall茅
• 刊名：Inorganic Chemistry
• 出版年：2014
• 出版时间：June 16, 2014
• 年：2014
• 卷：53
• 期：12
• 页码：5941-5949
• 全文大小：397K
• 年卷期：v.53,no.12(June 16, 2014)
• ISSN：1520-510X

文摘

Polyoxometalates (POMs) are inorganic entities featuring extensive and sometimes unusual redox properties. In this work, several experimental techniques as well as density functional theory (DFT) calculations have been applied to identify and assess the relevance of factors influencing the redox potentials of POMs. First, the position of the Mo substituent atom in the Wells鈥揇awson structure, 伪₁- or 伪₂-P₂W₁₇Mo, determines the potential of the first 1e^{鈥?/sup> reduction wave. For P₂W_18鈥?i>xMo_x systems containing more than one Mo atom, reduction takes place at successively more positive potentials. We attribute this fact to the higher electron delocalization when some Mo oxidizing atoms are connected. After having analyzed the experimental and theoretical data for the monosubstituted 伪₁- and 伪₂-P₂W₁₇Mo anions, some relevant facts arise that may help to rationalize the redox behavior of POMs in general. Three aspects concern the stability of systems: (i) the favorable electron delocalization, (ii) the unfavorable e鈥?/sup>鈥揺鈥?/sup> electrostatic repulsion, and (iii) the favorable electron pairing. They explain trends such as the second reduction wave occurring at more positive potentials in 伪₁- than in 伪₂-P₂W₁₇Mo, and also the third electron reduction taking place at a less negative potential in the case of 伪₂, reversing the observed behavior for the first and the second waves. In P₂W₁₇V derivatives, the nature of the first 鈥渄鈥?electron is more localized because of the stronger oxidant character of VV. Thus, the reduction potentials as well as the computed reduction energies (REs) for the second reduction of either isomer are closer to each other than in Mo-substituted POMs. This may be explained by the lack of electron delocalization in monoreduced P₂W₁₇VIV systems.}