EXAFS Study into the Speciation of Metal Salts Dissolved in Ionic Liquids and Deep Eutectic Solvents

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• 作者：Jennifer M. Hartley ; Chung-Man Ip ; Gregory C. H. Forrest ; Kuldip Singh ; Stephen J. Gurman ; Karl S. Ryder ; Andrew P. Abbott ; Gero Frisch
• 刊名：Inorganic Chemistry
• 出版年：2014
• 出版时间：June 16, 2014
• 年：2014
• 卷：53
• 期：12
• 页码：6280-6288
• 全文大小：307K
• 年卷期：v.53,no.12(June 16, 2014)
• ISSN：1520-510X

文摘

The speciation of metals in solution controls their reactivity, and this is extremely pertinent in the area of metal salts dissolved in ionic liquids. In the current study, the speciation of 25 metal salts is investigated in four deep eutectic solvents (DESs) and five imidazolium-based ionic liquids using extended X-ray absorption fine structure. It is shown that in diol-based DESs M^I ions form [MCl₂]^{鈭?/sup> and [MCl₃]2鈥?/sup> complexes, while all MII ions form [MCl₄]2鈥?/sup> complexes, with the exception of NiII, which exhibits a very unusual coordination by glycol molecules. This was also found in the X-ray crystal structure of the compound [Ni(phen)₂(eg)]Cl₂路2eg (eg = ethylene glycol). In a urea-based DES, either pure chloro or chloro鈥搊xo coordination is observed. In [C₆mim][Cl] pure chloro complexation is also observed, but coordination numbers are smaller (typically 3), which can be explained by the long alkyl chain of the cation. In [C₂mim][SCN] metal ions are entirely coordinated by thiocyanate, either through the N or the S atom, depending on the hardness of the metal ion according to the hard-soft acid-base principle. With weaker coordinating anions, mixed coordination between solvent and solute anions is observed. The effect of hydrate or added water on speciation is insignificant for the diol-based DESs and small in other liquids with intermediate or strong ligands. One of the main findings of this study is that, with respect to metal speciation, there is no fundamental difference between deep eutectic solvents and classic ionic liquids.}