Insight on Interactions in Binary Mixtures of [EMIM][N(CN)2] with iso- and tert-Butanol: Measurements, Correlations, and DFT Calculations

Abstract

The densities (ρ), speeds of sound (u), and viscosities (η) of pure ionic liquid (IL, [EMIM][N(CN)₂]), solvents, iso-butanol (i-BuOH), and tert-butanol (t-BuOH) and of its binary mixtures were experimentally measured using a high-precision vibrating tube densitometer (ρ and u) and an automated falling ball microviscometer (η) as functions of the mole fraction of IL (x₁) at T = 298.15–323.15 K and p = 0.1 MPa. Experimentally measured values of ρ, u, and η were used to evaluate excess/deviation parameters, and these parameters are correlated utilizing the Redlich–Kister polynomial equation. Correlations were also performed for the excess molar volumes (V_m^E) of each binary mixture using the Prigogine–Flory–Patterson equation. Forces of attraction that exist between the ions of IL and IL-solvent mixtures are well discussed. Density functional theory (DFT) was also applied to establish the possible molecular interactions between the ions of IL ([EMIM]⁺and [N(CN)₂]⁻) and the IL-solvent mixtures, revealing interactions at the D3-B3LYP/6–311++G(d,p) level of theory. Moreover, various molecular properties, including structures, frontier molecular orbitals, electrostatic potentials, atomic charges, dipole moments, interaction energies, and reactivity descriptors, were obtained at the same level of theory.