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.

Intrinsic Structure of the Interface of Partially Miscible Fluids: An Application to Ionic Liquids

“…43,54,55,77,78,80 Nonetheless, the possibility of forming weaker associations between cations and water was also evidenced experimentally and computationally through H atoms attached to the imidazolium ring, with a preference to interact with H2. 79,80 Figure 10: 2D radial distribution functions calculated in the (x,y) plane (i.e. the plane of the macroscopic surface) between the O atom of surface water molecules and either the central atom (N or P, respectively) of NTf − 2 and PF − 6 anions (a), or the 3 ring H atoms of BMIM cations at the surface of phases rich in either BMIM NTf 2 (b) or BMIM PF 2 (c).…”

Structural organization and phase behaviour of 1-butyl-3-methylimidazolium hexafluorophosphate: an high pressure Raman spectroscopy study

“…[29][30][31][32][33] Using these techniques, crystalline polymorphism in [bmim][X], with X = Cl and Br, was studied. 29,32,33 At ambient pressure, in the liquid state, the two mentioned rotational isomers of the butyl chain (the GA and AA ones) coexist in the [bmim] cation. Upon compression up to 900 MPa, the GA conformer becomes progressively de-stabilised.…”

High Pressure Phase Behavior of Two Imidazolium-Based Ionic Liquids, [bmim][BF4] and [bmim][PF6]

“…Generally, RTILs are classified into several groups depending on the cationic series, imidazolium, pyridinium, and alphatic quaternary ammonium series. Most of studies so far concern with the results at atmospheric pressure, but recently an increasing number of works using high pressure is reported (Chang et al, 2007(Chang et al, , 2008a(Chang et al, , 2008b(Chang et al, , 2008cSu et al, 2009Su et al, , 2010Umebayashi et al, 2009aUmebayashi et al, , 2009b. A merit of the use of high pressure as a varialbe is summarized as follows.…”