Molecular Force Field for Ionic Liquids Composed of Triflate or Bistriflylimide Anions (original) (raw)
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Structural analysis of ionic liquids with symmetric and asymmetric fluorinated anions
The Journal of Chemical Physics
Ionic liquids with relatively low viscosities and broad windows of electrochemical stability are often constructed by pairing asymmetric cations with bisfluorosulfonylimide (FSI −) or bistrifylimide (NTf − 2) anions. In this work, we systematically studied the structures of ILs with these anions and related perfluoro bis-sulfonylimide anions with asymmetry and/or longer chains: (fluorosulfonyl)(trifluoromethylsulfonyl)imide (BSI − 0,1), bis(pentafluoroethylsulfonyl)imide (BETI −), and (trifluoromethylsulfonyl)(nonafluorobutylsulfonyl)imide (BSI − 1,4) using high energy X-ray scattering and molecular dynamics (MD) simulations methods. 1alkyl-3-methylimidazolium cations with short (ethyl, Im + 2,1) and longer (octyl, Im + 1,8) hydrocarbon chains were selected to examine how the sizes of nonpolar hydrocarbon and fluorous chains affect IL structures and properties. In comparison to these, we also computationally explored the structure of ionic liquids with anions having longer fluorinated tails.
The Journal of Chemical Physics, 2018
We study ionic liquids composed 1-alkyl-3-methylimidazolium cations and bis(trifluoromethylsulfonyl)imide anions ([CnMIm][NTf2]) with varying chain-length n = 2, 4, 6, 8 by using molecular dynamics simulations. We show that a reparametrization of the dihedral potentials as well as charges of the [NTf2] anion leads to an improvment of the force field model introduced by Köddermann et al. [ChemPhysChem, 8, 2464 (2007)] (KPL-force field). A crucial advantage of the new parameter set is that the minimum energy conformations of the anion (trans and gauche), as deduced from ab initio calculations and Raman experiments, are now both well represented by our model. In addition, the results for [CnMIm][NTf2] show that this modification leads to an even better agreement between experiment and molecular dynamics simulation as demonstrated for densities, diffusion coefficients, vaporization enthalpies, reorientational correlation times, and viscosities. Even though we focused on a better representation of the anion conformation, also the alkyl chain-length dependence of the cation behaves closer to the experiment. We strongly encourage to use the new NGKPL force field for the [NTf2] anion instead of the earlier KPL parameter set for computer simulations aiming to describe the thermodynamics, dynamics and also structure of imidazolium based ionic liquids.
Journal of Physical Chemistry B, 2007
Thermodynamics, structure, and dynamics of an ionic liquid based on a quaternary ammonium salt with ether side chain, namely, N-ethyl-N,N-dimethyl-N-(2-methoxyethyl)ammonium bis(trifluoromethanesulfonyl)imide, MOENM 2 E TFSI, are investigated by molecular dynamics (MD) simulations. Average density and configurational energy of simulated MOENM 2 E TFSI are interpreted with models that take into account empirical ionic volumes. A throughout comparison of the equilibrium structure of MOENM 2 E TFSI with previous results for the more common ionic liquids based on imidazolium cations is provided. Several time correlation functions are used to reveal the microscopic dynamics of MOENM 2 E TFSI. Structural relaxation is discussed by the calculation of simultaneous space-time correlation functions. Temperature effects on transport coefficients (diffusion, conductivity, and viscosity) are investigated. The ratio between the actual conductivity and the estimate from ionic diffusion by the Nernst-Einstein equation indicates that correlated motion of neighboring ions in MOENM 2 E TFSI is similar to imidazolium ionic liquids. In line with experiment, Walden plot of conductivity and viscosity indicates that simulated MOENM 2 E TFSI should be classified as a poor ionic liquid.
Systematic Refinement of Canongia Lopes-Pádua Force Field for Pyrrolidinium-Based Ionic Liquids
The journal of physical chemistry. B, 2015
Reliable force field (FF) is a central issue in successful prediction of physical chemical properties via computer simulations. While Canongia Lopes-Pádua (CL&P) FF provides good to excellent thermodynamics and structure of pure room-temperature ionic liquids (RTILs), it suffers from drastically and systematically underestimated ionic motion. This occurs due to neglected partial electron transfer from the anion to the cation, resulting in unphysically small simulated self-diffusion and conductivity and high shear viscosities. We report a systematic refinement of the CL&P FF for six pyrrolidinium-based RTILs (1-N-butyl-1-methylpyrrolidinium dicyanamide, triflate, bis(fluorosulfonyl)imide, bis(trifluoromethanesulfonyl)imide, tetrafluoroborate, chloride). The elaborated procedure accounts for specific cation-anion interactions in the liquid phase. Once these interactions are described effectively, experimentally determined transport properties can be reproduced with an acceptable accur...
Generic force fields for ionic liquids
Journal of Molecular Liquids, 2014
Ionic liquids have been intensively studied during the last decade, but many questions still remain unresolved. From the computational side there is the lack of good transferable force fields for molecular simulations that would allow accurate theoretical predictions and interpretations of the properties of ionic liquids. Within this article a method is described that allows for the derivation of partial charges for ionic liquids since they play a particular important role, particularly for a liquid that consists entirely of ions. Our partial charges are carefully determined in such a way that they incorporate in an average way the influence of polarization effects of the neighboring ions in a bulk situation thereby reducing the total ionic charge to values less than one. When combined with our recently introduced method for the optimization of the short-range interactions [1] we have a well described route to develop generic force fields for ionic liquids. In this article we describe our results for the partial charges for the three imidazolium based liquids [MMIM] + ,[EMIM] + , and [BMIM] + for three different anions.
The Importance of Ionic Liquids and Applications on Their Molecular Modeling
Computational Models for Biomedical Reasoning and Problem Solving, 2019
Ionic liquids are salts with melting points generally below 100 °C made of entirely ions by the combination of a large cation and a group of anions. Some ionic liquids are found to have therapeutic properties due to their toxic effects (e.g., anticancer, antibacterial, and antifungal properties). The determination of the most stable molecular structures, that is, the lowest energy conformer of these ionic liquids with versatile biological activities, is of particular importance. Density function theory (DFT) based on quantum mechanical calculation method, one of the molecular modeling methods, is widely used in physics and chemistry to determine the electronic structures of these stable geometries and molecules. With the theory, the energy of the molecule is determined by using the electron density instead of the wave function. It is observed that the theoretical models developed on the ionic liquids in the literature are in agreement with the experimental results because of electro...
2011
Recently, we introduced a new force field (FF) to simulate transport properties of imidazolium-based room-temperature ionic liquids (RTILs) using a solid physical background. In the present work, we apply this FF to derive thermodynamic, structure, and transport properties of the mixtures of 1-butyl-3-methylimidazolium tetrafluoroborate, [BMIM][BF4], and acetonitrile (ACN) over the whole composition range. Three approaches to derive a force field are formulated based on different treatments of the ion-ion and ion-molecule Coulomb interactions using unit-charge, scaled-charge and floating-charge approaches. The simulation results are justified with the help of experimental data on specific density and shear viscosity for these mixtures. We find that a phenomenological account (particularly, simple scaled-charge model) of electronic polarization leads to the best-performing model. Remarkably, its validity does not depend on the molar fraction of [BMIM][BF4] in the mixture. The derived...
Structural Chemistry, 2022
Free-energy calculations based on molecular simulations provide access to a wide range of thermodynamic properties such as the solubility and partitioning of a molecule in and between various phases. It is demonstrated how molecular dynamics free-energy simulations may be used to obtain the solubilities of primary alcohols and n-alkanes in water and binding affinities of primary alcohols to a-cyclodextrin. The equivalence of two distinct routes to calculate binding free energies is shown leading to the conclusion that host-guest binding affinities may be used to probe the underlying molecular force field.