Experimental and Theoretical Study of Two Pyridinium-Based Ionic Liquids

Thermophysical properties of two pyridinium-based ionic liquids, 1-ethyl-2-methylpyridinium bis(trifluoromethylsulfonyl)imide and 1-propyl-2-methylpyridinium bis(trifluoromethylsulfonyl)imide, have been measured from 278.15 to 323.15 K, with a temperature step of 2.5 K. The properties measured were: densities, speeds of sound, refractive indices, surface tensions, isobaric molar heat capacities, electrical conductivities and viscosities. Thermal properties were also recorded in the temperature range from 100 to 320 K. From the experimental results coefficients of thermal expansion, isentropic compressibilities, molar refraction and surface enthalpies and entropies have been determined. Moreover, a theoretical study has been performed using ab initio calculations, level of theory HF/6-31G(d). From this study, we have obtained qualitative information about the magnitude and the directionality of the cation–anion interactions which allows a better understanding of the physico-chemical properties of these ionic liquids.