Thermophysical Properties and Quantum Chemical Calculations of 1-Butyl-3-methylimidazolium Trifluoromethanesulfonate ([BMIM][CF3SO3]) in Molecular Organic Solvent Mixtures at Various Temperatures

Abstract

The thermophysical properties of the pure ionic liquid, 1-butyl-3-methylimidazolium trifluoromethanesulfonate ([BMIM][CF₃SO₃]) and solvents, 2-methoxyethanol (2-MEOH) and 2-propoxyethanol (2-PEOH), along with their binary mixtures [BMIM][CF₃SO₃] + 2-MEOH and [BMIM][CF₃SO₃] + 2-PEOH, including densities (ρ), sound velocities (u), and dynamic viscosities(η), have been measured experimentally over entire mole fractions and the temperature range of 298.15 to 323.15 K at a constant pressure, 1 atm. The excess molar volumes (V^E), dynamic viscosities deviations (Δη), and isentropic compressibilities deviations (Δκ_s) have been calculated. The Redlich–Kister polynomial is used to fit the derived parameters (V^E, Δη, Δκ_s) and determine the R² values, standard deviations, and fitted coefficients. Furthermore, the Prigogine–Flory–Patterson (PFP) theory was applied to V^E for binary mixtures. In addition, Fourier Transform Infrared (FTIR) spectroscopy has been applied to probe interactions through key functional groups involved in hydrogen bonding of the ionic liquid (IL) in binary mixtures interactions. Additionally, density functional theory (DFT) has been employed to reveal interactions at the atomic scale in the IL and binary mixtures by using the dispersion corrected DFT, i.e., D3-B3LYP with the 6-311G (d, p) basis set. This study explores the solvent effects via counterpoise energy correction. Moreover, HOMO–LUMO, reduced density gradient (RDG), non-covalent interactions (NCI), and reactivity descriptors have been calculated. The RDG and NCI plots illustrate the noncovalent interaction, and reactivity descriptors quantify the strength and stability of the interactions.