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In this study, we aim at understanding the influence of dispersion correction on the ab initio molecular dynamics simulations of ionic liquid (IL) systems. We investigated a large bulk system of the 1-butyl-3-methylimidazolium triflate IL and a small cluster system of ethylamine in ethylammonium nitrate both under periodic boundary conditions. The large system displays several changes upon neglect of dispersion correction, the most striking one is the surprising decrease of the well-known microheterogeneity which is accompanied by an increase of side chain hydrogen atom-anion interplay. For the diffusion coefficient, we observe a correction towards experimental behavior in terms of the cation becoming faster than the anion with dispersion correction. Changes in the electronic structure upon dispersion correction are reflected in larger/smaller dipole moments for anions/cations also seen in the calculated IR spectrum. The energetics of different ion pair dimer subsystems (polar and non-polar) are in accordance with the analysis of the trajectories: A detailed balance in the ionic liquid system determines its particular behavior. While the overall interaction terms for dispersion-corrected calculations are higher, the decrease in microheterogeneity upon inclusion of dispersion interaction becomes obvious due to the relation between all contributions to polar-polar terms. For the small system, we clearly observe the well known behavior that the hybrid functionals show higher reaction barriers than the pure generalized gradient approximation (GGA) functionals. The correction of dispersion reduces the discrepancies in some cases. Accounting for the number of jumps, we observe that dispersion correction reduces the discrepancies from 50% to less than 10%. [ABSTRACT FROM AUTHOR]

Ionische Flüssigkeiten (ILs) variieren stark in ihrer Wechselwirkung mit CO2. Es wird ein einfaches theoretisches Verfahren vorgeschlagen, mit dem sich das Absorptionsverhalten von ILs vorhersagen lässt. Während starke Wechselwirkungen der IL-Anionen mit CO2 chemische Absorption bedeuten, weisen schwache auf physikalische Absorption hin. Eine Abschätzung mit klarer Trennung zwischen chemischer und physikalischer Absorption kann leicht erhalten werden, indem die Geometrie in Gegenwart eines Solvatationsmodells optimiert wird statt wie bisher nur in der Gasphase. Aus diesen solvatisierten Geometrien lassen sich Gibbs-Energien erhalten, die sehr gut mit experimentellen Werten übereinstimmen. Somit können die berechneten Gibbs-Energien mit vermessenen Kapazitäten korreliert werden. Vielversprechende Anionen für den Entwurf von ILs für reversible chemische CO2-Absorption können durch berechnete Gibbs-Reaktionsenergien definiert werden. Für diese Kandidaten lassen sich wiederum die Kapazitäten aus der eben erwähnten Korrelation abschätzen. [ABSTRACT FROM AUTHOR]

Wepresent a first principles molecular dynamics study of carbondioxide solvation by protic ionic liquids using ethylammonium nitrateas an example solvent. Microheterogeneity of the alkyl chains andthe extended hydrogen bond network could be observed. Thus, the entirestructure of the investigated protic ionic liquid mixed with CO2closely resembles the one of the pure liquid. Our data indicatesthat CO2most likely creates an energy loss due to enteringthe liquid via the too-small voids. But this is fully compensatedby specific attractive interactions of CO2with the cationand anions of ethylammonium nitrate. This result might serve as anexplanation for the question of why the volume of the ionic liquidis not increasing through CO2uptake. The CO2cluster formation, which shows a structure similar to supercriticalCO2, is guided by the dominance of the nonpolar groupsin the CO2solvation shell. [ABSTRACT FROM AUTHOR]

We present a theoretical study of carbene formation from the 1-ethyl-3-methylimidazoliumacetate ionic liquid in the absence and presence of CO2in gas and liquid phase. Although CO2physisorption constitutesa precursory step of chemisorption (the CO2’s reactionwith carbenes, which forms from cations via proton abstraction byanions), it also enables a very stable CO2–anionassociate. However, this counteracts the chemical absorption by reducingthe basicity of the anion and the electrophilicity of the CO2, which is reflected by charge transfer. Accordingly, the observablecarbene formation in the gas phase is hindered in the presence ofCO2. In the neat liquid, the carbene formation is alsosuppressed by the charge screening compared to the case of the gasphase; nevertheless, indications for carbene incidents appear. Interestingly,in the CO2-containing liquid we detect more carbene-likeincidents than in the neat one, which is caused by the way CO2is solvated. Despite the weakness of the CO2–cationinteraction, the CO2–anion associate is distortedby cations, which can be seen in longer associate distances and reduced“binding” energies. While the single solvating anionis shifted away from CO2, many more solvating cations approachit compared to the case of the gas phase. This leads to the conclusionthat while the ionic liquid effect stabilizes charged species, introducingneutral species such as CO2provides an opposite trend,leading to an inverse ionic liquid effect with the facilitation ofcarbene formation and thus of chemical absorption. [ABSTRACT FROM AUTHOR]

Ionic liquids (ILs), vary strongly in their interaction with CO2. We suggest simple theoretical approach to predict the CO2 absorption behavior of ILs. Strong interaction of the CO2 with the IL anions corresponds to chemical absorption whereas weak interaction indicates physical absorption. A predictive estimate with a clear distinction between physical and chemical absorption can be simply obtained according to geometries optimized in the presence of a solvation model instead of optimizing it only in gas phase as has been done to date. The resulting Gibbs free energies compare very well with experimental values and the energies were correlated with experimental capacities. Promising anions, for ionic liquids with reversible CO2 absorption properties can be defined by a reaction Gibbs free energy of absorption in the range of -30 to 16 kJ mol(-1)., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

In the reaction of 1-ethyl-3-methylimidazolium acetate [C2C1Im][OAc] ionic liquid with carbon dioxide at 125 °C and 10 MPa, not only the known N-heterocyclic carbene (NHC)-CO2 adduct I, but also isomeric aNHC-CO2 adducts II and III were obtained. The abnormal NHC-CO2 adducts are stabilized by the presence of the polarizing basic acetate anion, according to static DFT calculations and ab initio molecular dynamics studies. A further possible reaction pathway is facilitated by the high basicity of the system, deprotonating the initially formed NHC-CO2 adduct I, which can then be converted in the presence of the excess of CO2 to the more stable 2-deprotonated anionic abnormal NHC-CO2 adduct via the anionic imidazolium-2,4-dicarboxylate according to DFT calculations on model compounds. This suggests a generalizable pathway to abnormal NHC complex formation., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)