Prediction of Melting Points for Ionic Liquids

Abstract

Melting points are important for the specific application of ionic liquids. Although many different ionic liquids are possible, melting points are known only for relatively few. Derivation of melting point QSPRs (Quantitative Structure-Property Relationships) for ionic liquids would therefore greatly aid in the molecular design of new compounds. A new class of ionic liquids, based on 1-substituted-4-amino-1,2,4-triazolium bromide, nitrate, and nitrocyanamide salts were recently synthesized and their melting points measured. After optimizing the molecular geometries of the cations of the ionic liquids using ab initio quantum chemical methods, we derived melting-point QSPRs from molecular orbital and electrostatic descriptors. Good correlations with the experimental data were found. The correlation coefficients for three-parameter melting-point QSPRs exceed 0.8. Although some of the descriptors that appear in our QSPRs were designed to describe chemical reactions, we infer that they serve in this study to quantify interactions between the cation and anion or between the cations.