Theoretical study on 1-butyl-3-methyl-4,5-dibromoimidazolium dis(trifluoromethane sulfonyl)imide and 1-(3,4-dibromobutyl)-3-methylimidazolium dis(trifluoromethane sulfonyl) imide ionic liquids

The density functional method was employed to study 1-butyl-3-methyl-4,5-dibromoimidazolium dis(trifluoromethane sulfonyl)imide ([BMIM-Br]+[Tf2N]−) and 1-(3,4-dibromobutyl)-3-methylimidazolium dis(trifluoromethane sulfonyl)imide ([Br-BMIM]+[Tf2N]−) ionic liquids. The calculated results reveal that intra-pair interactions in both 1-pair [BMIM-Br]+[Tf2N]− and 1-pair [Br-BMIM]+[Tf2N]− are hydrogen bonds. The N prefers to interact with C2-proton of the cation ring. The order of hydrogen bonding strength is N > O > F. The inter-pair interactions in 2-pair [BMIM-Br]+[Tf2N]− and 2-pair [Br-BMIM]+[Tf2N]− are halogen bonds and hydrogen bonds, respectively, which is ascribed to more positive bromine atoms in [BMIM-Br]+ than [Br-BMIM]+.