Density functional calculations have been performed to investigate the interactions of two neutral ionic liquids of 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM](+)[PF6] ) and 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM](+)[BF4] ) and pyridine/hexane. The calculated results reveal that the predominant interactions of C2-H2 center dot center dot center dot F hydrogen bonds in [BMIM](+)[PF6] or [BMIM](+)[BF4] were not altered by pyridine/hexane. The interactions between [BMIM](+)[PF6] /[BMIM](+)[BF4] and pyridine are stronger than that between [BMIM](+)[PF6] /[BMIM](+)[BF4] and hexane. The interactions between [BMIM](+)[PF6] and pyridine/hexane are stronger than that between [BMIM](+)[BF4] and pyridine/hexane. (c) 2012 Elsevier B.V. All rights reserved.