Thermodynamic Study of 1,4-Bis(3-methylimidazolium-1-yl)butane Bis(trifluoromethylsulfonyl)imide ([C4(MIm)2][NTf2]2) from 6 to 350 K

The molar heat capacity of 1,4-bis(3-methylimidazolium-1-yl)butane bis(trifluoromethylsulfonyl)imide dicationic ionic compound ([C₄(MIm)₂][NTf₂]₂) has been studied over the temperature range from 6 to 350 K by adiabatic calorimetry. In the above temperature interval, this compound has been found to form crystal, liquid, and supercooled liquid. For [C₄(MIm)₂][NTf₂]₂, the temperature of fusion <i>T</i>°_fus = (337.88 ± 0.01) K has been determined by the fractional melting experiments, the enthalpy of fusion Δ_fus<i>H</i>° = (52.79 ± 0.28) kJ mol^-1 has been measured using the calorimetric method of continuous energy input, and the entropy of fusion Δ_fus<i>S</i>° = (156.2 ± 1.7) J K^-1 mol^-1 has also been evaluated. The standard thermodynamic functions of the studied dicationic ionic compound, namely, the heat capacity <i>C</i>_p°(<i>T</i>), the enthalpy [<i>H</i>°(<i>T</i>) - <i>H</i>°(0)], the entropy <i>S</i>°(<i>T</i>) and the Gibbs free energy [<i>G</i>°(<i>T</i>) - <i>H</i>°(0)] have been calculated on the basis of the experimental data for the temperature range up to 350 K. The results have been discussed and compared with those available in the literature and in the NIST Ionic Liquids Database (ILThermo) for monocationic ionic compounds.