Temperature and pressure dependence of the infrared spectrum of 1-ethyl-3-methylimidazolium trifluoromethanesulfonate ionic liquid

The infrared absorption spectrumof 1-ethyl-3-methylimidazoliumtrifluoromethanesulfonate (EMI-TfO) was investigated at ambient pressure and variable temperatures between 120 and 330 K, or at roomtemperature and variable pressures up to 10 GPa. Upon cooling, the ionic liquid crystallizes; on the contrary, upon compression no evidence of crystallization can be obtained from the infrared spectra. Moreover, Density Functional Theory (DFT) calculations were applied to gain a better description of the ionic couple. The !B97X-D functional, including not only the empirical dispersion corrections but also the presence of a polar solvent, gives a good agreement with the infrared spectrum and suggests that TfO resides above the plane of the imidazolium, with the shorter distance between the O atom of the anion and the C2 atom of the imidazolium ring equal to 2.23 A.