Structural Characterization of Ionic Liquids by X-Ray Absorption Spectroscopy

Ionic liquids are receiving substantial attention as a result of their unique properties as solvents for chemical transformations. Their versatility depends on the fact that their properties can be tuned by varying the cation and the anion, and a molecular based characterization of ILs is crucial to select the desired properties for specific applications.
P. D'Angelo et al., J. Chem. Phys. 135, 074505 (2011).

X-ray absorption spectroscopy has been used to unveil the bromide ion local coordination structure in 1-alkyl-3-methylimidazolium bromide [Cnmim]Br ionic liquids (ILs) with different alkyl chains. The XAS spectrum of 1-ethyl-3-methylimidazolium bromide has been found to be different from those of the other members of the series, from the butyl to the decyl derivatives, that have all identical XAS spectra. This result indicates that starting from 1-buthyl-3-methylimidazolium bromide the local molecular arrangement around the bromide anion is the same independently from the length of the alkyl chain, and that the imidazolium head groups in the liquid ILs with long alkyl chains assume locally the same

orientation as in the [C4mim]Br crystal.With this study we show that the XAS technique is an effective direct tool for unveiling the local structural arrangements around selected atoms in ILs. Retrieve article X-Ray absorption spectroscopy investigatio of 1-alkyl-3-methylimidazolium bromide salts P. D’Angelo, A. Zitolo, V. Migliorati, E. Bodo, G. Aquilanti, J. L. Hazemann, D. Testemale, G. Mancini, and R. Caminiti The Journal of Chemical Physics 135, 074505 (2011). 10.1063/1.3625920