Microheterogeneities in Ionic‐Liquid–Methanol Solutions Studied by FTIR Spectroscopy, DFT Calculations and Molecular Dynamics Simulations

Abstract

The interest in ionic liquids (ILs) is steadily increasing because of their fascinating physicochemical properties and because of their broad range of applications in synthesis, separation, catalysis and electrochemistry. However, the multiplicity of their uses strongly depends on a molecular understanding of their exceptional properties. One key to a better understanding of their unique properties are spectroscopic studies of ionic liquids in conventional organic solvents in combination with DFT calculations and molecular dynamics simulations. Therefore we investigated the mixtures of the imidazolium-based ionic liquid [C(2)mim][NTf(2)] with methanol. Caused by the amphiphilic character of methanol both liquids are miscible over the whole mixture range. The scope of this work is to study the changes in the IL network upon dilution and to investigate the formation of methanol clusters embedded in the IL matrix. The mixtures were studied by FTIR spectroscopy in the mid-infrared region. The formation of methanol clusters was studied from the OD stretching vibrational bands between 2300 and 2800 cm(-1). The cluster populations of methanol could be derived from molecular dynamics simulations for the same mixtures. Weighting the DFT calculated frequencies by the cluster populations we could reproduce the measured spectra in the OD stretching region up to X(MeOH)=0.5. Above X(MeOH)=0.8, strong formation of self-methanol clusters takes place resulting in increasing diffusion coefficients related to decreasing dynamical heterogeneities. Thus we obtained a deep understanding of the solute-solvent and solute-solute interactions as well as information about the presence of microheterogeneities in the mixtures.

Electrode–Electrolyte Interfacial Processes in Ionic Liquids and Sensor Applications

“…This means that cation-anion coulombic attraction is driving the overall structure, with local steric effects influencing the final orientation of ions. Table 2.4 lists the IR response of C-H bond in ILs [112][113][114][115][116][117][118][119]. confirming this fact [125][126][127][128].…”

“…But they are still detectable [112][113][114][115]. Those conformation differences are present in the fingerprint region of IR (under 1,000 cm ) [112][113][114][115]. B-F of BF 4 is located at 924 cm −1 and 1,312 cm −1 , and P-F of PF 6 is about 843 cm −1 [116][117][118][119].…”

“…Furthermore, the intensity of both bands gradually decreases in the premelting region due to the predominance of the trans conformation in the liquid state. But they are still detectable [112][113][114][115]. Those conformation differences are present in the fingerprint region of IR (under 1,000 cm ) [112][113][114][115].…”

Probing Structures of Interfacial 1-Butyl-3-Methylimidazolium Trifluoromethanesulfonate Ionic Liquid on Nano-Aluminum Oxide Surfaces Using High-Pressure Infrared Spectroscopy

“…It is known that the hydrogen bond cooperativity due to concerted charge transfer can greatly enhance the strength of the individual hydrogen bonds involved in the coupling [25]. Hydrogen-bonding non-additivity and the size of clusters are suggested to be responsible for the enhancement of hydrogen bonding [25,26]. Thus, the anomalous jump in frequency at 0.4 GPa can be attributed to both the cooperative and geometric effects of blue-shifting hydrogen bonds.…”

The effect of pressure on cation–cellulose interactions in cellulose/ionic liquid mixtures

“…4,5 Negligible volatilities and a broad range of liquid states make ionic liquids attractive alternatives to volatile organic solvents, leading to discussions of ionic liquids as green solvents. [4][5][6][7][8][9] Various studies have been performed to elucidate the role of weak hydrogen bonding (C-HÁ Á ÁO or C-HÁ Á ÁX) in the structure of ionic liquids. Based on the results of previous studies, ionic liquids may possess hydrogen bonds, but the role of hydrogen bonding in ionic liquids is not well understood.…”