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Ralf Ludwig - One of the best experts on this subject based on the ideXlab platform.
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dispersion and hydrogen bonding rule why the vaporization enthalpies of aprotic ionic liquids are significantly larger than those of protic ionic liquids
Angewandte Chemie, 2016Co-Authors: Dzmitry H Zaitsau, Vladimir N Emelyanenko, Peter Stange, Christoph Schick, Sergey P Verevkin, Ralf LudwigAbstract:It is well known that gas-phase experiments and computational methods point to the dominance of dispersion forces in the molecular association of hydrocarbons. Estimates or even quantification of these weak forces are complicated due to solvent effects in solution. The dissection of interaction energies and quantification of dispersion interactions is particularly challenging for polar systems such as ionic liquids (ILs) which are characterized by a subtle balance between Coulomb interactions, hydrogen bonding, and dispersion forces. Here, we have used vaporization enthalpies, Far-Infrared Spectroscopy, and dispersion-corrected calculations to dissect the interaction energies between cations and anions in aprotic (AILs), and protic (PILs) ionic liquids. It was found that the higher total interaction energy in PILs results from the strong and directional hydrogen bonds between cation and anion, whereas the larger vaporization enthalpies of AILs clearly arise from increasing dispersion forces between ion pairs.
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controlling the subtle energy balance in protic ionic liquids dispersion forces compete with hydrogen bonds
Angewandte Chemie, 2015Co-Authors: Koichi Fumino, Peter Stange, Verlaine Fossog, Dietmar Paschek, Rolf Hempelmann, Ralf LudwigAbstract:The properties of ionic liquids are determined by the energy-balance between Coulomb-interaction, hydrogen- bonding, and dispersion forces. Out of a set of protic ionic liquids (PILs), including trialkylammonium cations and methylsulfonate and triflate anions we could detect the transfer from hydrogen-bonding to dispersion-dominated interaction between cation and anion in the PIL ((C6H13)3NH)(CF3SO3). The characteristic vibrational features for both ion-pair species can be detected and assigned in the Far-Infrared spectra. Our approach gives direct access to the relative strength of hydro- gen-bonding and dispersion forces in a Coulomb-dominated system. Dispersion-corrected density functional theory (DFT) calculations support the experimental findings. The dispersion forces could be quantified to contribute about 2.3 kJ mol 1 per additional methylene group in the alkyl chains of the ammonium cation. Investigating noncovalent interactions in liquids is still a challenge. (1-5) This is in particular true for ionic liquids, where a subtle energy balance between Coulomb interaction, hydrogen bonding, and dispersion forces results in unique properties. (4, 5) Although the Coulomb interaction is the dominant intermolecular interaction, hydrogen-bonding and dispersion forces may become crucial for the structure and dynamics of ionic liquids. (6, 7) We could show recently that local and directional hydrogen bonding in aprotic ionic liquids can result in more fluid rather than more viscous liquids. (7) For thermodynamic properties, such as enthalpies of vaporiza- tion, it was observed that they increase nearly linearly with the increasing alkyl-chain length of the imidazolium cation. A comparison with n-alkanes and n-alcohols showed that the linear increase in intermolecular interaction strength with each methylene group results from dispersion forces only. (8) There is no doubt that both, H-bonding and dispersion interactions are of importance for IL properties. However, the dissection and quantification of the different noncovalent interactions is still a difficult endeavor. Hydrogen bonding is somewhat easier to analyze, because H-bonds are both short- ranged and highly directional. The crucial role of dispersion forces in ILs is currently studied intensively. (9-14) Grimme and Kirchner could show that London dispersion interactions contribute significantly to the overall interaction energy in aprotic ionic liquids. (10) As benchmark they used accurate coupled-cluster methods. Izgorodina et al. showed that calcu- lated energies are closely related to measured melting points if dispersion forces are taken into account. (14) However, there is no quantification of dispersion forces in ionic liquids reported from experiment. Thus it is the purpose of the present work to quantify those noncovalent interactions and to describe the competition between hydrogen bonding and dispersion-forces in a Coulomb-dominated fluid. In partic- ular, it is shown that dispersion forces can outbalance hydrogen bonding with increasing temperature. The exper- imental results from Far-Infrared Spectroscopy are supported by DFT calculations with and without taking explicitly dispersions forces into account. (10, 15-17)
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analyzing the interaction energies between cation and anion in ionic liquids the subtle balance between coulomb forces and hydrogen bonding
Journal of Molecular Liquids, 2014Co-Authors: Koichi Fumino, Ralf LudwigAbstract:Abstract Potential applications of ionic liquids depend on the properties of this class of liquid material. To a large extent the structure and properties of these Coulomb systems are determined by the intermolecular interactions among anions and cations. In particular the subtle balance between Coulomb forces, hydrogen bonds and dispersion forces is of great importance for the understanding of ionic liquids. All these issues are addressed by using a suitable combination of experimental and theoretical methods including specially synthesized imidazolium-based ionic liquids, far infrared Spectroscopy (FIR) and density functional theory (DFT) calculations. The key statement is that although ionic liquids consist solely of anions and cations and Coulomb forces are the dominating interaction, a local and directional interaction such as hydrogen bonding has significant influence on the structure and properties of ionic liquids. In this review we mainly summarize the results we achieved within our project of the priority programme “Ionic Liquids” (SPP 1191), which has been funded by the German Science Foundation (DFG) between 2008 and 2012.
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the influence of hydrogen bonding on the physical properties of ionic liquids
Physical Chemistry Chemical Physics, 2011Co-Authors: Koichi Fumino, Dzmitry H Zaitsau, Sergey P Verevkin, Tim Peppel, Monika Geppertrybczynska, Jochen K Lehmann, Martin Kockerling, Ralf LudwigAbstract:Potential applications of ionic liquids depend on the properties of this class of liquid material. To a large extent the structure and properties of these Coulomb systems are determined by the intermolecular interactions among anions and cations. In particular the subtle balance between Coulomb forces, hydrogen bonds and dispersion forces is of great importance for the understanding of ionic liquids. The purpose of the present paper is to answer three questions: Do hydrogen bonds exist in these Coulomb fluids? To what extent do hydrogen bonds contribute to the overall interaction between anions and cations? And finally, are hydrogen bonds important for the physical properties of ionic liquids? All these questions are addressed by using a suitable combination of experimental and theoretical methods including newly synthesized imidazolium-based ionic liquids, far infrared Spectroscopy, terahertz Spectroscopy, DFT calculations, differential scanning calorimetry (DSC), viscometry and quartz-crystal-microbalance measurements. The key statement is that although ionic liquids consist solely of anions and cations and Coulomb forces are the dominating interaction, local and directional interaction such as hydrogen bonding has significant influence on the structure and properties of ionic liquids. This is demonstrated for the case of melting points, viscosities and enthalpies of vaporization. As a consequence, a variety of important properties can be tuned towards a larger working temperature range, finally expanding the range of potential applications.
P M Petroff - One of the best experts on this subject based on the ideXlab platform.
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shell structure and electron electron interaction in self assembled inas quantum dots
EPL, 1996Co-Authors: M Fricke, A Lorke, J P Kotthaus, G Medeirosribeiro, P M PetroffAbstract:Using Far-Infrared Spectroscopy, we investigate the excitations of self-organized InAs quantum dots as a function of the electron number per dot, 1 ≤ ne ≤ 6, which is monitored in situ by capacitance Spectroscopy. Whereas the well-known two-mode spectrum is observed when the lowest (s-) states are filled, we find a rich excitation spectrum for ne ≥ 3, which reflects the importance of electron-electron interaction in the present, strongly non-parabolic confining potential. From capacitance Spectroscopy we find that the electronic shell structure in our dots gives rise to a distinct pattern in the charging energies which strongly deviates from the monotonic behavior of the Coulomb blockade found in mesoscopic or metallic structures.
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shell structure and electron electron interaction in self assembled inas quantum dots
arXiv: Condensed Matter, 1996Co-Authors: M Fricke, A Lorke, J P Kotthaus, G Medeirosribeiro, P M PetroffAbstract:Using Far-Infrared Spectroscopy, we investigate the excitations of self-organized InAs quantum dots as a function of the electron number per dot, 1
Koichi Fumino - One of the best experts on this subject based on the ideXlab platform.
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controlling the subtle energy balance in protic ionic liquids dispersion forces compete with hydrogen bonds
Angewandte Chemie, 2015Co-Authors: Koichi Fumino, Peter Stange, Verlaine Fossog, Dietmar Paschek, Rolf Hempelmann, Ralf LudwigAbstract:The properties of ionic liquids are determined by the energy-balance between Coulomb-interaction, hydrogen- bonding, and dispersion forces. Out of a set of protic ionic liquids (PILs), including trialkylammonium cations and methylsulfonate and triflate anions we could detect the transfer from hydrogen-bonding to dispersion-dominated interaction between cation and anion in the PIL ((C6H13)3NH)(CF3SO3). The characteristic vibrational features for both ion-pair species can be detected and assigned in the Far-Infrared spectra. Our approach gives direct access to the relative strength of hydro- gen-bonding and dispersion forces in a Coulomb-dominated system. Dispersion-corrected density functional theory (DFT) calculations support the experimental findings. The dispersion forces could be quantified to contribute about 2.3 kJ mol 1 per additional methylene group in the alkyl chains of the ammonium cation. Investigating noncovalent interactions in liquids is still a challenge. (1-5) This is in particular true for ionic liquids, where a subtle energy balance between Coulomb interaction, hydrogen bonding, and dispersion forces results in unique properties. (4, 5) Although the Coulomb interaction is the dominant intermolecular interaction, hydrogen-bonding and dispersion forces may become crucial for the structure and dynamics of ionic liquids. (6, 7) We could show recently that local and directional hydrogen bonding in aprotic ionic liquids can result in more fluid rather than more viscous liquids. (7) For thermodynamic properties, such as enthalpies of vaporiza- tion, it was observed that they increase nearly linearly with the increasing alkyl-chain length of the imidazolium cation. A comparison with n-alkanes and n-alcohols showed that the linear increase in intermolecular interaction strength with each methylene group results from dispersion forces only. (8) There is no doubt that both, H-bonding and dispersion interactions are of importance for IL properties. However, the dissection and quantification of the different noncovalent interactions is still a difficult endeavor. Hydrogen bonding is somewhat easier to analyze, because H-bonds are both short- ranged and highly directional. The crucial role of dispersion forces in ILs is currently studied intensively. (9-14) Grimme and Kirchner could show that London dispersion interactions contribute significantly to the overall interaction energy in aprotic ionic liquids. (10) As benchmark they used accurate coupled-cluster methods. Izgorodina et al. showed that calcu- lated energies are closely related to measured melting points if dispersion forces are taken into account. (14) However, there is no quantification of dispersion forces in ionic liquids reported from experiment. Thus it is the purpose of the present work to quantify those noncovalent interactions and to describe the competition between hydrogen bonding and dispersion-forces in a Coulomb-dominated fluid. In partic- ular, it is shown that dispersion forces can outbalance hydrogen bonding with increasing temperature. The exper- imental results from Far-Infrared Spectroscopy are supported by DFT calculations with and without taking explicitly dispersions forces into account. (10, 15-17)
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analyzing the interaction energies between cation and anion in ionic liquids the subtle balance between coulomb forces and hydrogen bonding
Journal of Molecular Liquids, 2014Co-Authors: Koichi Fumino, Ralf LudwigAbstract:Abstract Potential applications of ionic liquids depend on the properties of this class of liquid material. To a large extent the structure and properties of these Coulomb systems are determined by the intermolecular interactions among anions and cations. In particular the subtle balance between Coulomb forces, hydrogen bonds and dispersion forces is of great importance for the understanding of ionic liquids. All these issues are addressed by using a suitable combination of experimental and theoretical methods including specially synthesized imidazolium-based ionic liquids, far infrared Spectroscopy (FIR) and density functional theory (DFT) calculations. The key statement is that although ionic liquids consist solely of anions and cations and Coulomb forces are the dominating interaction, a local and directional interaction such as hydrogen bonding has significant influence on the structure and properties of ionic liquids. In this review we mainly summarize the results we achieved within our project of the priority programme “Ionic Liquids” (SPP 1191), which has been funded by the German Science Foundation (DFG) between 2008 and 2012.
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the influence of hydrogen bonding on the physical properties of ionic liquids
Physical Chemistry Chemical Physics, 2011Co-Authors: Koichi Fumino, Dzmitry H Zaitsau, Sergey P Verevkin, Tim Peppel, Monika Geppertrybczynska, Jochen K Lehmann, Martin Kockerling, Ralf LudwigAbstract:Potential applications of ionic liquids depend on the properties of this class of liquid material. To a large extent the structure and properties of these Coulomb systems are determined by the intermolecular interactions among anions and cations. In particular the subtle balance between Coulomb forces, hydrogen bonds and dispersion forces is of great importance for the understanding of ionic liquids. The purpose of the present paper is to answer three questions: Do hydrogen bonds exist in these Coulomb fluids? To what extent do hydrogen bonds contribute to the overall interaction between anions and cations? And finally, are hydrogen bonds important for the physical properties of ionic liquids? All these questions are addressed by using a suitable combination of experimental and theoretical methods including newly synthesized imidazolium-based ionic liquids, far infrared Spectroscopy, terahertz Spectroscopy, DFT calculations, differential scanning calorimetry (DSC), viscometry and quartz-crystal-microbalance measurements. The key statement is that although ionic liquids consist solely of anions and cations and Coulomb forces are the dominating interaction, local and directional interaction such as hydrogen bonding has significant influence on the structure and properties of ionic liquids. This is demonstrated for the case of melting points, viscosities and enthalpies of vaporization. As a consequence, a variety of important properties can be tuned towards a larger working temperature range, finally expanding the range of potential applications.
Anouk M Rijs - One of the best experts on this subject based on the ideXlab platform.
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fingerprints of inter and intramolecular hydrogen bonding in saligenin water clusters revealed by mid and far infrared Spectroscopy
Physical Chemistry Chemical Physics, 2017Co-Authors: Daniel J Bakker, Arghya Dey, Daniel P Tabor, Qin Ong, Jerome Mahe, Mariepierre Gaigeot, Edwin L Sibert, Anouk M RijsAbstract:Saligenin (2-(hydroxymethyl)phenol) exhibits both strong and weak intramolecular electrostatic interactions. The bonds that result from these interactions compete with intermolecular hydrogen bonds once saligenin binds to one or more water molecules. Infrared (IR) ultraviolet (UV) ion-dip Spectroscopy was used to study isolated saligenin-(H2O)n clusters (n = 1-3) in the far- and mid-IR regions of the spectrum. Both harmonic and anharmonic (coupled local modes and Born-Oppenheimer molecular dynamics) quantum chemical calculations were applied to assign cluster geometries to the measured spectra, and to assign vibrational modes to all spectral features measured for each cluster. The hydrated clusters with n = 1 and 2 have geometries that are quite similar to benzyl alcohol-water clusters, whereas the larger clusters with n = 3 show structures equivalent to the isolated water pentamer. Systematic shifts in the frequencies of three hydrogen bond (H-bond) deforming modes, namely OH stretching, OH torsion and H-bond stretching, were studied as a function of the hydrogen bond strength represented by either the OH bond length or the H-bond length. The shifts of the frequencies of these three modes correlate linearly to the OH length, despite both intra- and intermolecular H-bonds being included in this analysis. The OH torsion vibration displays the largest frequency shift when H-bonded, followed by the OH stretching vibrations and finally the H-bond stretching frequency. The frequency shifts of these H-bond deforming modes behave non-linearly as a function of the H-bond length, asymptotically approaching the frequency expected for the non H-bonded modes. The nonlinear behavior was quantified using exponential functions.
M Fricke - One of the best experts on this subject based on the ideXlab platform.
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shell structure and electron electron interaction in self assembled inas quantum dots
EPL, 1996Co-Authors: M Fricke, A Lorke, J P Kotthaus, G Medeirosribeiro, P M PetroffAbstract:Using Far-Infrared Spectroscopy, we investigate the excitations of self-organized InAs quantum dots as a function of the electron number per dot, 1 ≤ ne ≤ 6, which is monitored in situ by capacitance Spectroscopy. Whereas the well-known two-mode spectrum is observed when the lowest (s-) states are filled, we find a rich excitation spectrum for ne ≥ 3, which reflects the importance of electron-electron interaction in the present, strongly non-parabolic confining potential. From capacitance Spectroscopy we find that the electronic shell structure in our dots gives rise to a distinct pattern in the charging energies which strongly deviates from the monotonic behavior of the Coulomb blockade found in mesoscopic or metallic structures.
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shell structure and electron electron interaction in self assembled inas quantum dots
arXiv: Condensed Matter, 1996Co-Authors: M Fricke, A Lorke, J P Kotthaus, G Medeirosribeiro, P M PetroffAbstract:Using Far-Infrared Spectroscopy, we investigate the excitations of self-organized InAs quantum dots as a function of the electron number per dot, 1
