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Raman and ab initio study of the conformational isomerism in the 1‐ethyl‐3‐methyl‐imidazolium bis(trifluoromethanesulfonyl)imide ionic liquid
Author(s) -
Lassègues J. C.,
Grondin J.,
Holomb R.,
Johansson P.
Publication year - 2007
Publication title -
journal of raman spectroscopy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.748
H-Index - 110
eISSN - 1097-4555
pISSN - 0377-0486
DOI - 10.1002/jrs.1680
Subject(s) - conformational isomerism , raman spectroscopy , ionic liquid , imide , chemistry , ion , crystallography , metastability , ab initio , ionic bonding , population , ab initio quantum chemistry methods , molecule , organic chemistry , physics , demography , sociology , optics , catalysis
The calculated and experimental Raman spectra of the (EMI + )TFSI − ionic liquid, where EMI + is the 1‐ethyl‐3‐methylimidazolium cation and TFSI − the bis(trifluoromethanesulfonyl)imide anion, have been investigated for a better understanding of the EMI + and TFSI − conformational isomerism as a function of temperature. Characteristic Raman lines of the planar (p) and non‐planar (np) EMI + conformers are identified using the reference (EMI + )Br − salt. The anion conformer of C 2 symmetry is confirmed to be more stable than the cis ( C 1 ) one by 4.5 ± 0.2 kJ mol −1 . At room temperature, the population of trans ( C 2 ) anions and np cations is 75 ± 2% and 87 ± 4%, respectively. Fast cooling quenches a metastable glassy phase composed of mainly C 2 anion conformers and p cation conformers, whereas slow cooling gives a crystalline phase composed of C 1 anion conformers and of np cation conformers. Copyright © 2006 John Wiley & Sons, Ltd.