Use of ab initio calculations toward the rational design of room temperature ionic liquids

Ionic liquids are gaining substantial interest as alternative reaction media. Despite the overwhelming amount of evidence suggesting a relationship between their structure and melting point, there still remains the problem of selectively choosing a particular ionic pair that will produce a liquid at room temperature. Ionic liquids based on 1-alkyl-3-methylimidazolium halides have been investigated using ab initio calculations utilizing Gaussian 98 and the 6-31G* and 6-31+G* basis sets. The calculated interaction energy was found to increase in magnitude with decreasing alkyl chain length at the Hartree-Fock level, although no trend was found to exist with increasing anionic radius. Correlations between melting point and interaction energy were investigated. Linear trends were found to exist in the 1-n-butyl-3-methylimidazolium (Bmim) halide series as well as the 1-alkyl-3-methylimidazolium iodide series.