Density functional study on ionic liquid of 1-propyl-4,5-dibromo-3-methylimidazolium bromide

The density functional method and DNP basis set were employed to study 1-pair, 2-pair, and 3-pair of cation–anion interactions of 1-propyl-4,5-dibromo-3-methylimidazolium bromides. The calculated results reveal that H2 atoms of 1-propyl-4,5-dibromo-3-methylimidazolium form hydrogen bondings with Br−. The natural bond orbital (NBO) and atoms in molecules (AIM) analyzes show that halogen bondings between Br− anion and imidazolium ring substituted bromine atoms were formed in the gas phase, in agreement with the crystal phase of 1-propyl-4,5-dibromo-3-methylimidazolium bromide which is governed by both hydrogen bondings and halogen bondings.