Study on the relationship between the interaction energy and the melting point of amino acid cation based ionic liquids

The DFT method B3LYP together with basis set 6-311++G(d,p) was used to study the interaction energy between cation and anion in a series of new generation ionic liquids whose cations are derived from amino acids. The geometry optimization of gas-phase ion pairs of over 30 chosen ionic liquid and related analogues (some salts with high melting points) was performed first, then the interaction energies of the series of molecules between cation and anion were calculated and the basis set superposition error (BSSE) was corrected by counterpoise method (CP). Combining the experimental melting point data, it was found that for the amino acid cation based ionic liquids, there exists good correlation between the melting points and the interaction energies, and the corresponding linear equation of melting point on interaction energy was obtained. The results show the probability of designing ILs with the help of quantum chemistry study in the future exploitation.