jp502124y_si_001.pdf (100.81 kB)
Molecular Structure and Interactions in the Ionic Liquid 1‑Ethyl-3-methylimidazolium Bis(Trifluoromethylsulfonyl)imide
journal contribution
posted on 2014-04-03, 00:00 authored by Nilesh
R. Dhumal, Kristina Noack, Johannes Kiefer, Hyung J. KimElectronic structure theory (density
functional and Møller–Plesset
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–anion 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–H---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.