Molecular Structure and Interactions in the Ionic Liquid 1-Ethyl-3-methylimidazolium Bis(Trifluoromethylsulfonyl)imide

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• 作者：Nilesh R. Dhumal ; Kristina Noack ; Johannes Kiefer ; Hyung J. Kim
• 刊名：Journal of Physical Chemistry A
• 出版年：2014
• 出版时间：April 3, 2014
• 年：2014
• 卷：118
• 期：13
• 页码：2547-2557
• 全文大小：513K
• 年卷期：v.118,no.13(April 3, 2014)
• ISSN：1520-5215

文摘

Electronic structure theory (density functional and M酶ller鈥揚lesset perturbation theory) and vibrational spectroscopy (FT-IR and Raman) are employed to study molecular interactions in the room-temperature ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide. Different conformers of a cation鈥揳nion pair based on their molecular interactions are simulated in the gas phase and in a dielectric continuum solvent environment. Although the ordering of conformers in energy varies with theoretical methods, their predictions for three lowest energy conformers in the gas phase are similar. Strong C鈥揌---N interactions between the acidic hydrogen atom of the cation imidazole ring and the nitrogen atom of the anion are predicted for either the lowest or second lowest energy conformer. In a continuum solvent, different theoretical methods yield the same ion-pair conformation for the lowest energy state. In both phases, the density functional method predicts that the anion is in a trans conformation in the lowest energy ion pair state. The theoretical results are compared with experimental observations from Raman scattering and IR absorption spectroscopies and manifestations of the molecular interactions in the vibrational spectra are discussed. The directions of the frequency shifts of the characteristic vibrations relative to the free anion and cation are explained by calculating the difference electron density coupled with electron density topography.