Ion association and solvation behaviours of the ionic liquids [Bupy] Cl, [Bupy]Br, [Bupy][BF₄] and [Bupy][PF₆] in some binary mixed solvents at various temperatures

Herein, for the first time, this article provides the transport properties and the association behaviour of pyridinium family-based ionic liquids in dilute solution systems. Investigation of molecular interactions via accurate molar conductance (Lambda) measurements are reported for solution systems of various 1-butylpyridinium-based ionic liquids, namely [Bupy]Cl, [Bupy]Br, [Bupy][BF4] and [Bupy][PF6], in 10%, 30% and 50% (w/w) DMF-H2O and MeOH-H2O mixtures at various temperatures. The conductance data are examined via the Fuoss-Edelson equation in terms of the ionic association constant (KA) and the limiting molar conductance (Lambda(o)). It is shown that the type of anion affects the ionic association constants and limiting molar conductance for each of the systems studied. For the [Bupy].cation, the limiting molar conductance of the system was found to decrease in the order Cl-> B-r-> [BF4](-)> [PF6](-), with the ionic association constants following the order [BF4](-)> [PF6](-)> Br->Cl- in the solvents used; limiting molar conductance are also found to increase when the temperature is increased in all instances. All four of these electrolytes were solvated to a different extent by the mixture solvents, and their KA is influenced significantly by ionic solvation. Furthermore, the transport properties including limiting ionic conductance (lambda(+/-)(o)), the transference numbers (t(+/-)), ionic mobility (u(+/-)), diffusion coefficient(D-o)for individual ions, Walden product (Lambda(o)eta(o)), hydrodynamic radii (R-H) and the activation energy of the transport process (Ea)are also estimated and discussed. Based on the temperature variations, the association constants have been examined to obtain the thermodynamic functions (Delta G(A)(o), Delta S-A(o) and Delta H-A(o) changes) for all systems. The results are discussed in terms of ion-ion and ion-solvent interactions, hydrogen bond formation, structural aspects, and configurational theory. It is anticipated that this information will be beneficial when attempting to modify of the ionic liquids' conductance according to the type of anion, and physical properties of the solvent mixtures.