Exploring enthalpies of formation of imidazolium-, pyridinium-, and pyrrolidinium-based ionic liquids with dicyanamide anion using quantum chemical methods.

In this work, quantum chemical calculations have been performed on the ionic liquids based on imidazolium, pyridinium, and pyrrolidinium cations with the dicyanamide anion. The dispersion-corrected B3LYP exchange-correlation functional was used to optimize geometries. Enthalpies of formation were calculated at the high-level G3(MP2) theory by employing both the atomization energy and reaction enthalpy approaches. There exists a very good agreement between the predicted enthalpies of formation and available experimental values. For the first time, the enthalpies of formation have been predicted for 21 ion pairs with no available experimental data. The calculated enthalpies of formation are decreased with increasing alkyl chain length. Linear correlations were observed between enthalpy of formation and number of carbon atoms in the alkyl side-chain for all of the studied series of cations. Regardless of the cation type, the contribution of each CH 2 group in the alkyl chain to the enthalpy of formation was also determined. • Enthalpies of formation of dicyanamide based ionic liquids were calculated. • Atomization and isodesmic reactions at the G3(MP2) were used. • Good agreement with experimental data, where available, was achieved. • The calculated enthalpy of formation was found to decrease with increasing alkyl chain length. • A linear correlation was observed between enthalpy of formation and number of carbon atoms in the alkyl side-chain of cations. [ABSTRACT FROM AUTHOR]