Synthesis, Characterization, and Physicochemical Properties of New [Emim][BF₃X] Complex Anion Ionic Liquids

A new series of complex anion ionic liquids (ILs) [Emim][BF₃X] (X = CH₃SO₃, EtSO₄, HSO₄, Tosylate) were synthesized and characterized by nuclear magnetic resonance, elemental analysis, differential scanning calorimetry analysis, and thermogravimetry. The physicochemical properties of these ILs, such as density, viscosity, conductivity, and surface tension, were measured and correlated with thermodynamic and empirical equations in the temperature range of 293.15–358.15 K under ambient conditions, and the thermal expansion coefficient, standard molar entropy, lattice potential energy, viscosity activation energy, surface enthalpy, and surface entropy were further calculated from experimental values. According to the temperature-dependent viscosity and conductivity, [Emim][BF₃X] ILs follow the Walden rule, and they are classified as “good (or super) ionic liquids”.