Ionic association and conductance of ionic liquids in dichloromethane at temperatures from 278.15 to 303.15 K

Abstract

The electrical conductances of very dilute solutions of the ionic liquids 1-ethyl-3-methylimidazolium tetrafluoroborate [emim] [BF 4 ] and 1-butyl-3-methylimidazolium tetrafluoroborate [bmim] [BF 4 ] in the low-permittivity solvent dichloromethane have been measured in the temperature range from 278.15 to 303.15 K at 5 K intervals. The data was analyzed assuming the possible presence of contact (CIP) and solvent-separated (SSIP) ion pairs in the solution on the basis of lcCM model to obtain ionic association constants, K A , and the limiting molar conductivities, Λ o , of these electrolytes. The examined ionic liquids are strongly associated in dichloromethane over the whole temperature range. From the temperature dependence of the limiting molar conductivities, the Eyring's activation enthalpy of charge transport was determined. The thermodynamic functions such as Gibbs energy, entropy, and enthalpy of the process of ion pair formation were calculated from the temperature dependence of the association constants.

Ionic Liquids: Simple or Complex Electrolytes?

“…This behavior can be ascribed to higher ion association in DCM due to the lower dielectric constant. The value, obtained in diluted solutions by Borun and Bald 35 (K A = 479 at 298.15 K, Table 1) confirms strongly this assumption. Even more -also in other solvents the decrease of conductivity after the maximum could be ascribed to stronger ion association.…”

A review on conductometric studies of electrolytes in mixed solvent systems to understand ion-ion and ion-solvent interactions

“…They have discussed the effect of temperature, solvent structure and properties, the cation and anion of the ionic liquid on the limiting molar conductivity and the ionic association, as well as ion transport processes and thermodynamic properties of ionic association. A Borun and his coworkers have also studied the conductance behavior of the above mentioned imidazolium ions in dichloromethane [48], 1-Butanol [49], N,Ndimethyl acetamide [50], propan 2-ol [51] [53]. For all the systems they have analysed their experimental conductance data by following low concentration Chemical Model (lcCM).…”

A review on conductometric studies of electrolytes in mixed solvent systems to understand ion-ion and ion-solvent interactions

“…They have discussed the effect of temperature, solvent structure and properties, the cation and anion of the ionic liquid on the limiting molar conductivity and the ionic association, as well as ion transport processes and thermodynamic properties of ionic association. A Borun and his coworkers have also studied the conductance behavior of the above mentioned imidazolium ions in dichloromethane [48], 1-Butanol [49], N,N-dimethyl acetamide [50], propan 2-ol [51] [53]. For all the systems they have analysed their experimental conductance data by following low concentration Chemical Model (lcCM).…”