Solvation and microscopic properties of ionic liquid/acetonitrile mixtures probed by high-pressure infrared spectroscopy

Abstract

The microscopic features of binary mixtures formed by an ionic liquid (EMI(+)TFSA(-) or EMI(+)FSA(-)) and a molecular liquid (acetonitrile or methanol) have been investigated by high-pressure infrared spectroscopy. On the basis of its responses to changes in pressure and concentration, the imidazolium C-H appears to exist at least in two different forms, i.e., isolated and associated structures. The weak band at approximately 3102 cm(-1) should be assigned to the isolated structure. CD(3)CN can be added to change the structural organization of ionic liquids. The compression of an EMI(+)TFSA(-)/CD(3)CN mixture leads to the increase in the isolated C-H band intensity. Nevertheless, the loss in intensity of the isolated structures was observed for EMI(+)FSA(-)/CD(3)CN mixtures as the pressure was elevated. In other words, the associated configuration is favored with increasing pressure by debiting the isolated form for EMI(+)FSA(-)/CD(3)CN mixtures. The stronger C-H...F interactions in EMI(+)FSA(-) may be one of the reasons for the remarkable differences in the pressure-dependent results of EMI(+)TFSA(-) and EMI(+)FSA(-).

Evidence that Acetonitrile is Sensitive to Different Interaction Sites of Ionic Liquids as Revealed by Excess Spectroscopy

“…[51][52][53][54] Nevertheless,t here should be ar elationship between the observed and calculated frequencies. [56][57][58] In contrast to the present work, the interactions between the ionic liquid anda cetonitrilew ere not mentioned in the reportb yU mebayashi et al, [47] who even used the term "isolated structure" to describe the ionic liquid in dilute acetonitrile. Figure 2B,t he negative peak corresponds to the species in neat acetonitrile.…”

“…[47] They observed an increasei nt he imidazolium CÀHi ntensity at approximately 3102 cm À1 upon mixing acetonitrile with the ionic liquid. [47] They observed an increasei nt he imidazolium CÀHi ntensity at approximately 3102 cm À1 upon mixing acetonitrile with the ionic liquid.…”

Local structures of ionic liquids in the presence of gold under high pressures

“…It is well known that high pressures almost invariably cause phase changes and the pure ionic liquids will most likely be frozen, i.e., in solid form. [27][28][29] The sharper structures revealed in Fig. 2(b) is in part due to the conformation drift and anisotropic environment in a solid structure.…”

“…The pressures used to investigate chemical systems typically range from ambient to several GPa; such pressures mainly change intermolecular distances and affect conformations. [27][28][29][30] Previous high-pressure measurements indicated that acetonitrile and dimethyl sulfoxide can be added to change the structural organization of ionic liquids. 27,28 Under ambient pressure, Raman spectra indicate that the more thermodynamically stable butyl structure of the cations is the gauche-anti (GA) and all-anti forms for [BMI][Br] and [BMI][Cl], respectively.…”

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.…”