Quantum chemical investigation of the structures of ionic liquids based on 1-ethyl-3-methylimidazolium halides: IR spectra and hydrogen bonds

Hydrogen bonds, structures, and vibrational spectra of 1-ethyl-3-methylimidazolium halides ([emim][Hal]) were analyzed in the framework of the Hartree—Fock method (HF/6-31G*, 6-31+G*) and the density functional theory (B3LYP/6-31G*, 6-31+G*, 6-31G**, 6-31+G**). It is shown that the use of the approximation of an isolated ion pair cation—anion is incorrect for the ionic liquids studied. It is more reasonable to consider “clusters” including at least two-three cations and being more appropriate models for the study of hydrogen bonds and vibrational spectra of ionic liquids of this type.