Monocationic and dicationic phosphonium based ionic liquids: Synthesis and properties

Abstract. In the current work, two monocationic ionic liquids (MILs) and two dicationic ionic liquids (DILs) with similar trihexyl(tetradecyl)phosphonium cation, [P66614]+ and different metal chloride anions such as trichlorostannate anion, [SnCl3]-, pentachlorozirconate anion, [ZrCl5]-, tetrachloronickelate(II) anion, [NiCl4]2- and tetrachlorocuprate(II) anion, [CuCl4]2- were successfully synthesized and characterized, respectively. The structures of ILs were confirmed using FT-IR spectroscopy and CHNS elemental analysis. The effect of temperature and anion type on thermophysical properties such as viscosity, density and refractive index were studied. Viscosity and density were measured within temperature range of 25 ℃ to 100 ℃. Moreover, thermal expansion coefficient, molecular volume, molar volume and free volume were derived from viscosity and density values. Refractive index values were measured in the temperature range of 10 ℃ to 60 ℃ and were used further to estimate the electronic polarizability using Lorenz-Lorentz equation. Thermal properties of the synthesized MILs and DILs were determined using thermogravimetric analyzer (TGA) and differential scanning calorimetry (DSC).