Depolarization of water in protic ionic liquids

Zahn, Stefan; Wendler, Katharina; Site, Luigi Delle; Kirchner, Barbara

doi:10.1039/c1cp20288j

Cited by 69 publications

(80 citation statements)

References 159 publications

(168 reference statements)

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“…Furthermore, it was reported that IL cations can exhibit a depolarization effect on water molecules. Thus, the dipole moment of water decreases with increasing IL concentration in several aprotic and protic ILs [122][123][124] , which can be counteracted in presence of strong hydrogen bond acceptor anions. Another interesting effect is also the formation of carbenes in presence of water 122 .…”

Section: Discussionmentioning

confidence: 99%

The properties of residual water molecules in ionic liquids: a comparison between direct and inverse Kirkwood–Buff approaches

Kobayashi

Reid

Shimizu

et al. 2017

Phys. Chem. Chem. Phys.

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We study the properties of residual water molecules at different mole fractions in dialkylimidazolium based ionic liquids (ILs), namely 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIM/BF4) and 1-butyl-3-methylimidazolium tetrafluoroborate (BMIM/BF4) by means of atomistic molecular dynamics (MD) simulations. The corresponding Kirkwood-Buff (KB) integrals for the water-ion and ion-ion correlation behavior are calculated by a direct evaluation of the radial distribution functions. The outcomes are compared to the corresponding KB integrals derived by an inverse approach based on experimental data. Our results reveal a quantitative agreement between both approaches, which paves a way towards a more reliable comparison between simulation and experimental results. The simulation outcomes further highlight that water even at intermediate mole fractions has a negligible influence on the ion distribution in the solution. More detailed analysis on the local/bulk partition coefficients and the partial structure factors reveal that water molecules at low mole fractions mainly remain in the monomeric state. A non-linear increase of higher order water clusters can be found at larger water concentrations. For both ILs, a more pronounced water coordination around the cations when compared to the anions can be observed, which points out that the IL cations are mainly responsible for water pairing mechanisms. Our simulations thus provide detailed insights in the properties of dialkylimidazolium based ILs and their effects on water binding.

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Section: Discussionmentioning

confidence: 99%

The properties of residual water molecules in ionic liquids: a comparison between direct and inverse Kirkwood–Buff approaches

Kobayashi

Reid

Shimizu

et al. 2017

Phys. Chem. Chem. Phys.

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“…Furthermore, it was found that local properties in ILs—like dipole fluctuations—could not be reproduced by static charges (even if they are sophisticated) in force field simulations. However, these play only a role if the treatment of the local behavior is necessary (e.g., IR or RAMAN spectroscopy), while for non‐local properties (e.g., transport properties) a simple charge scaling can be sufficient to account for charge transfer, as discussed in Chapter 4.…”

Section: Intermolecular Forcesmentioning

confidence: 99%

Multiresolution calculation of ionic liquids

Kirchner

Hollóczki

Lopes

et al. 2014

WIREs Comput Mol Sci

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115

165

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Ionic liquids-which are special solvents composed entirely of ions-are difficult albeit interesting to study for several reasons. Owing to the many possible cation and anion combinations that form ionic liquids, common properties are hard to classify for them, which makes the theoretical investigation crucial for ionic liquids. The system size, the amount of possible isomers including cation-anion orientation and coordination, as well as the rotation of the side chain(s) prevent the use of high-level electronic structure methods, and density functional theory is the method of choice. Dispersion forces-although they are small compared to electrostatics-play a major role in ionic liquids; therefore, methods that describe such kind of interplay are preferred. Between the cation and the anion, there is a sizable charge transfer, which has important consequences for molecular dynamics simulations and force field development. Already based on the first generation of force fields important discoveries were made, namely that ionic liquids are nanostructured. Moreover, it was possible to predict that their distillation is possible. Throughout the construction of these force fields, transferability was taken into account which allowed them to describe homologous series. For studying reactions in ionic liquid (IL) media, continuum models were found to improve the results. Ab initio molecular dynamics (AIMD) and quantum mechanics (QM)/molecular mechanics (MM) approaches are well suited for spontaneous events. In case of very large systems, such as cellulose in ionic liquids, coarse-grained methods are providing insight and are applied more frequently. This makes ionic liquids real multiscalar systems.

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“…[30] Many computational models have been developed that examined changes in IL solvent structure by dissolved water, often over the full concentration range. [31][32][33][34][35] At low water concentration, the models predict that the IL nanostructure is relatively unperturbed, but at high water content the system resembles aqueous solutions of ionic surfactants. However, these studies have overwhelmingly investigated aprotic ILs; largely absent are corresponding studies of PILs and experimental verification of the findings.…”

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confidence: 99%

How Water Dissolves in Protic Ionic Liquids

2012

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In recent years, ionic liquids (ILs) have emerged as useful chemical solvents for an enormous number of processes and technologies. [1,2] Their ions have more complex chemical structures than inorganic salts; by incorporating large, sterically mismatched anions and cations, ILs melt at low temperatures because, compared to typical inorganic salts, Coulombic attractions are weakened and lattice-packing arrangements frustrated. [3] ILs are regarded as "designer solvents", as molecular control over liquid properties is possible depending on how the ions are functionalized. Hydrogen bonding can play a key role in IL chemistry. [4][5][6] Whereas most inorganic salts cannot form hydrogen bonds and are dominated by electrostatic interactions between ions, many ILs have extensive H-bonding capacity. For example, H-bond donor and acceptor sites are created during synthesis of protic ionic liquids (PILs). [2] This enables some PILs to develop dense Hbond networks and thus mirrors a number of remarkable structural [5] and solvent [2] properties of water. Finally, ILs have the capacity to self-assemble, forming well-defined nanostructures in the bulk phase [7][8][9][10][11][12][13] as well as at interfaces. [3,[14][15][16] IL nanostructure arises because at least one of the ions (frequently the cation) is amphiphilic, with distinct charged and uncharged moieties. [9] This drives segregation of ionic and nonionic groups in ILs, reminiscent of self-assembly in aqueous surfactant mesophases. [3,12] Here we elucidate the bulk solvent structure of mixtures of a PIL, ethylammonium nitrate (EAN), and water ( Figure 1). EAN is one of the oldest known [17] and most extensively studied PILs. As EAN is completely miscible with water, this raises questions such as: how do EAN and water mix? Are the forces that lead to self-assembly in pure EAN [9] sufficient to maintain a solvophobic nanostructure? What is the nature of ion solvation in such mixtures? If nanostructure persists in aqueous mixtures and key solvent properties are retained, this will increase PIL utility by offering an additional mechanism for tuning liquid behavior and lowering the overall cost of the solvent medium.While primitive (continuum solvent) models of dilute aqueous electrolyte solutions are generally successful, understanding ion-water interactions and concentrated solutions has proved challenging, and is complicated in part by the absence of a satisfactory model for liquid water. [18,19] The structure in aqueous electrolyte solutions is understood in terms of Hofmeister [20] and hydrophobic [21] effects, which can only be probed using sophisticated experimental [22][23][24] and computational [25][26][27] techniques. Solvated ions induce a different local structure of water molecules in the first, and even the second or third solvation shells, to accommodate the dissolved species. This leads to ions being classified as either "structure making" or "structure breaking" through the creation of "solute cavities". [28] Recent, growing interest in IL/water mixtures h...

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Depolarization of water in protic ionic liquids

Cited by 69 publications

References 159 publications

The properties of residual water molecules in ionic liquids: a comparison between direct and inverse Kirkwood–Buff approaches

The properties of residual water molecules in ionic liquids: a comparison between direct and inverse Kirkwood–Buff approaches

Multiresolution calculation of ionic liquids

How Water Dissolves in Protic Ionic Liquids

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