Anion effect on the thermodynamic properties of alkylsilane-based ionic liquids

This work reports the thermodynamic study of several alkylsilane-based ILs paired with dicyanamide ([N(CN)₂]⁻), tricyanomethanide ([C(CN)₃]⁻), tetracyanoborate ([B(CN)₄]⁻) and trifluoromethanesulfonate ([OTf]) anions, [(SiCSiC)C₁im][X] (where [X] = [N(CN)₂]⁻, [C(CN)₃]⁻, [B(CN)₄]⁻, [OTf]). The heat capacity was determined at T = 298.15 K, and as a function of temperature, between 283 and 333 K. For this, high-precision drop microcalorimetry (Drop-Cp) and heat-conduction differential scanning microcalorimetry (HC-DSC) were used, respectively. The Knudsen effusion coupled with quartz crystal microbalance (KEQCM) technique was applied in the study of the vapor pressure of these ILs. Power compensation differential scanning calorimetry (DSC) was used to investigate the phase behavior of these ILs, while thermogravimetric analysis (TGA) was employed for the study of thermal stability. The differences in heat capacity between the various SiILs were shown to be essentially identical to those found in the [C _n C₁im]-based ILs. It was found excellent prediction of additivity models for the estimation of the heat capacity of SiILs. The volatility results revealed that the [NTf₂]-based SiIL is significantly more volatile than both the [B(CN)₄]⁻ and [OTf]-based SiILs, with the effect of the anion being identical to that found in [C _n C₁im]-based ILs. The findings reported in this work allow for a further understanding of the properties and thermodynamics of SiILs, revealing that the electrostatic interactions in the SiILs are essentially identical to those in n -alkyl-based ILs.