Low-temperature heat capacity and standard thermodynamic functions of the novel ionic liquid 1-(2-methoxyethyl)-3-ethyl imidazolium perrhenate

The ionic liquid 1-(2-methoxyethyl)-3-ethyl imidazolium perrhenate [C₂2O1IM][ReO₄] was prepared in the laboratory firstly, and its structure was confirmed by ¹H NMR and ¹³C NMR. The heat capacities were precisely measured in the temperature range from 78 to 392 K by means of a fully automated adiabatic calorimeter. For [C₂2O1IM][ReO₄], the melting temperature, standard molar heat capacity, molar enthalpy, and molar entropy of solid–liquid phase transition were determined to be (211.826 ± 0.130) K, (142.31 ± 0.34) J K⁻¹ mol⁻¹, (14.382 ± 0.046) kJ mol⁻¹, and (67.93 ± 0.22) J K⁻¹ mol⁻¹, respectively. And the experimental values of molar heat capacities were fitted to a polynomial equation using least square method in the appropriate temperature ranges. The thermodynamic functions (H_T − H_298.15) and (S_T − S_298.15) were also obtained from the heat capacity data in the experimental temperature range with an interval of 5 K.