Ionenspezies in Mischungen aus protischen ionischen Flüssigkeiten und Wasser: Übergang von Kontakt‐ zu solvensseparierten Ionenpaaren

Stange, Peter; Fumino, Koichi; Ludwig, Ralf

doi:10.1002/ange.201209609

Cited by 20 publications

(5 citation statements)

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“…Both spectra share a common vibrational feature around 70 cm −1 that is usually attributed to cage rattling of interacting ions and bending modes of directional intermolecular interaction 19. 20 The additional vibrational band at 106 cm −1 for TEAI can be clearly assigned to the + NH⋅⋅⋅I − interaction, which is strongly enhanced by hydrogen bonding 14. Consequently, this feature is missing in the spectrum of [Et 4 N][I].…”

Section: Resultsmentioning

confidence: 99%

Ion Pairing in Protic Ionic Liquids Probed by Far‐Infrared Spectroscopy: Effects of Solvent Polarity and Temperature

et al. 2014

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The cation-anion and cation-solvent interactions in solutions of the protic ionic liquid (PIL) [Et3NH][I] dissolved in solvents of different polarities are studied by means of far infrared vibrational (FIR) spectroscopy and density functional theory (DFT) calculations. The dissociation of contact ion pairs (CIPs) and the resulting formation of solvent-separated ion pairs (SIPs) can be observed and analyzed as a function of solvent concentration, solvent polarity, and temperature. In apolar environments, the CIPs dominate for all solvent concentrations and temperatures. At high concentrations of polar solvents, SIPs are favored over CIPs. For these PIL/solvent mixtures, CIPs are reformed by increasing the temperature due to the reduced polarity of the solvent. Overall, this approach provides equilibrium constants, free energies, enthalpies, and entropies for ion-pair formation in trialkylammonium-containing PILs. These results have important implications for the understanding of solvation chemistry and the reactivity of ionic liquids.

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Section: Resultsmentioning

confidence: 99%

Ion Pairing in Protic Ionic Liquids Probed by Far‐Infrared Spectroscopy: Effects of Solvent Polarity and Temperature

et al. 2014

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“…As discussed before for TEAMS, the vibrational band at 150 cm À1 in the FIR spectrum can be referred to the cation-anion interaction along the + N-HÁ Á ÁO À bond. 127,146 The well known feature of the low frequency water spectrum is the broad vibrational band at around 200 cm À1 which is assigned to the intermolecular interaction within the extended hydrogen bonding network of water. 48,[131][132][133][134] In Fig.…”

Section: Ion Speciationmentioning

confidence: 99%

Probing molecular interaction in ionic liquids by low frequency spectroscopy: Coulomb energy, hydrogen bonding and dispersion forces

Fumino

Reimann

Ludwig

2014

Phys. Chem. Chem. Phys.

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Ionic liquids are defined as salts composed solely of ions with melting points below 100 °C. These remarkable liquids have unique and fascinating properties and offer new opportunities for science and technology. New combinations of ions provide changing physical properties and thus novel potential applications for this class of liquid materials. To a large extent, the structure and properties of ionic liquids are determined by the intermolecular interaction between anions and cations. In this perspective we show that far infrared and terahertz spectroscopy are suitable methods for studying the cation-anion interaction in these Coulomb fluids. The interpretation of the measured low frequency spectra is supported by density functional theory calculations and molecular dynamics simulations. We present results for selected aprotic and protic ionic liquids and their mixtures with molecular solvents. In particular, we focus on the strength and type of intermolecular interaction and how both parameters are influenced by the character of the ions and their combinations. We show that the total interaction between cations and anions is a result of a subtle balance between Coulomb forces, hydrogen bonds and dispersion forces. For protic ionic liquids we could measure distinct vibrational modes in the low frequency spectra indicating clearly the cation-anion interaction characterized by linear and medium to strong hydrogen bonds. Using isotopic substitution we have been able to dissect frequency shifts related to pure interaction strength between cations and anions and to different reduced masses only. In this context we also show how these different types of interaction may influence the physical properties of ionic liquids such as the melting point, viscosity or enthalpy of vaporization. Furthermore we demonstrate that low frequency spectroscopy can also be used for studying ion speciation. Low vibrational features can be assigned to contact ion pairs and solvent separated ion pairs. In conclusion we showed how detailed knowledge of the low frequency spectra can be used to understand the change in interaction strength and structure by variation of temperature, solvent polarity and solvent concentration in ionic liquids and their mixtures with molecular solvents. In principle the used combination of methods is suitable for studying intermolecular interaction in pure molecular liquids and their solutions including additive materials such as nanoparticles.

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“…Recently, we reported the transition from CIPs to SIPs in mixtures of triethylammonium methylsulfonate [Et 3 NH]-[CH 3 SO 3 ] (TEAMS) and water. [33] Difference spectra of the mixtures in the far-infrared (FIR) region showed two absorption bands with changing absorption as a function of water concentration which could be assigned to different ion pair species. To overcome the strong interaction between anion and cation in this PIL, four water molecules per ion pair were needed to initiate this process.…”

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Equilibrium of Contact and Solvent‐Separated Ion Pairs in Mixtures of Protic Ionic Liquids and Molecular Solvents Controlled by Polarity

et al. 2013

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Ionenspezies in Mischungen aus protischen ionischen Flüssigkeiten und Wasser: Übergang von Kontakt‐ zu solvensseparierten Ionenpaaren

Cited by 20 publications

References 59 publications

Ion Pairing in Protic Ionic Liquids Probed by Far‐Infrared Spectroscopy: Effects of Solvent Polarity and Temperature

Ion Pairing in Protic Ionic Liquids Probed by Far‐Infrared Spectroscopy: Effects of Solvent Polarity and Temperature

Probing molecular interaction in ionic liquids by low frequency spectroscopy: Coulomb energy, hydrogen bonding and dispersion forces

Equilibrium of Contact and Solvent‐Separated Ion Pairs in Mixtures of Protic Ionic Liquids and Molecular Solvents Controlled by Polarity

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