title: Structural organization in aqueous solutions of 1-Butyl-3-methylimidazolium halides: a high-pressure infrared spectroscopic study on ionic liquids.
abstract: High-pressure infrared spectroscopy was applied to study the hydrogen-bonding structures of 1-butyl-3-methylimidazolium halides/D2O mixtures. No drastic changes were observed in the concentration dependence of the alkyl C-H band frequency at high concentration of 1-butyl-3-methylimidazolium chloride. Nevertheless, the alkyl C-H exhibits an increase in frequency upon dilution at low concentration. These observations may indicate a clustering of the alkyl groups at high concentration and the formation of a certain water structure around alkyl C-H groups in the water-rich region. The imidazolium C-H band at ca. 3051 cm(-1) displays a monotonic blue-shift in frequency as the sample was diluted at high concentration of 1-butyl-3-methylimidazolium chloride. That is, water can be added to change the structural organization of 1-butyl-3-methylimidazolium chloride in the ionic liquid-rich composition region by introducing water-imidazolium C-H interactions. Analyzing the pressure dependence of the imidazolium C-H stretches yielded anomalous nonmonotonic pressure-induced frequency shifts. This result may reflect the strengthening of C-H-O interactions between imidazolium C-H groups and the water clusters. Density functional theory calculations also revealed that the characteristic bonded C2-H vibration may be shifted via the modification of C2-H-Cl- associations.
authors.affiliation: Department of Chemistry, National Dong Hwa University, Shoufeng, Hualien 974, Taiwan. hcchang@mail.ndhu.edu.tw
authors.forename: Hai-Chou
authors.initials: HC
authors.lastname: Chang
authors.forename: Jyh-Chiang
authors.initials: JC
authors.lastname: Jiang
authors.forename: Chao-Yen
authors.initials: CY
authors.lastname: Chang
authors.forename: Jong-Chang
authors.initials: JC
authors.lastname: Su
authors.forename: Chao-Hsin
authors.initials: CH
authors.lastname: Hung
authors.forename: You-Chang
authors.initials: YC
authors.lastname: Liou
authors.forename: Sheng Hsien
authors.initials: SH
authors.lastname: Lin