Synthesis, experimental and theoretical vibrational studies of 1-methyl and 1,2-dimethyl, 3-propyl imidazolium bis(trifluoromethanesulfonyl) imide

In this study, two ionic liquids containing the bis(trifluoromethanesulfonyl)imide ( $$[(\hbox {CF}_{3}\hbox {SO}_{2})_{2}\hbox {N}^{-}]$$ ) anion are synthesized. The syntheses are based on an alkylation reaction of 1-methyl imidazole and 1,2-dimethyl imidazole followed by anion exchange. The obtained ILs are characterized by $$^{1}\hbox {H-NMR}$$ , $$^{13}\hbox {C-NMR}$$ , $$^{19}\hbox {F-NMR}$$ and FT-IR spectroscopy. Vibrational spectroscopy studies were conducted by infrared (FTIR/ATR), Raman spectroscopy and DFT calculations. The presence of methylation in the C2 position gives rise to specific marker bands in the Raman and IR spectra. In order to ascertain whether cation conformers are present in our ionic liquids, a computational study was performed using the density functional theory. The comparison of the experimental data and the computed spectra shows that three conformers of the imidazolium ions are present in both ionic liquids. Synopsis We synthesized and investigated the vibrational properties of two ionic liquids, namely, 1-methyl,3-propyl imidazolium bis(trifluoromethane-sulfonyl) imide ( $$[1\hbox {-MPrIM}^{+}][(\hbox {CF}_{3}\hbox {SO}_{2})_{2}\hbox {N}^{-}]$$ ) and 1,2-dimethyl,3-propyl imidazolium bis(trifluoromethane-sulfonyl) imide ( $$[1,2\hbox {-DMPrIM}^{+}][(\hbox {CF}_{3}\hbox {SO}_{2})_{2}\hbox {N}^{-}]$$ ). Methylation in the C2 position gives rise to specific marker bands in the Raman and IR spectra. The comparison of the experimental data and the computed spectra at DFT level shows that three conformers of the imidazolium ions are present in both ionic liquids.