On the origin of ionicity in ionic liquids. Ion pairing versus charge transfer

Hollóczki, Oldamur; Malberg, Friedrich; Welton, Tom; Kirchner, Barbara

doi:10.1039/c4cp01177e

Cited by 205 publications

(234 citation statements)

References 105 publications

(178 reference statements)

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“…Ion pairing [31], however, can also be defined via considering dynamical criteria, as has been proposed by Zhao et al [32] The two descriptors that may aid assessing the presence of IPs are how far and for how long two neighboring oppositely charged particles travel together in the solution. Hence, these descriptors may not only aid in the quantitative characterization of an ion pair but more importantly also in their qualitatively characterization.…”

Section: Resultsmentioning

confidence: 99%

En route formation of ion pairs at the ionic liquid–vacuum interface

et al. 2015

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An increasing lack of single ion cation-anion associations (ion pairing) in ionic liquids suggests a structural motif that stands in contradiction to the single ion pair structure of their vapor phase, which was evidenced by different experimental and theoretical studies. Therefore, a structural rearrangement has to occur en route from the liquid to the vapor. In this study, we propose a detailed four-step evaporation mechanism for ionic liquids, providing a refined perspective on the theory of this process based on the connection between ion pairing and volatility. The process involves diffusion of ions from the bulk to the surface, where they float around until a well-defined ion pair is formed with a counterion, leading to the departure from the surface into the vacuum. To assess the validity of this scheme, we performed a series of classical and ab initio molecular dynamics simulations based on the most sophisticated methods and force fields available for ionic liquids.

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Section: Resultsmentioning

confidence: 99%

En route formation of ion pairs at the ionic liquid–vacuum interface

et al. 2015

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“…All these methods, when used on ionic liquids with no constraint on the total charge of the ions, yield values smaller than the formal charge. [78][79][80] There are two interpretations: This may be either due to polarization or to charge transfer effects. Discriminating between these effects is a tricky issue, and it is rendered even more difficult by the fact that all the charge derivation methods provide different values for the same configuration and that even a given method yields different sets of charges depending on the conditions of the calculation (i.e.…”

Section: On the Use Of Reduced Charges In Non Polarizable Force Fmentioning

confidence: 99%

Simulations of room temperature ionic liquids: from polarizable to coarse-grained force fields

Salanne

2015

Phys. Chem. Chem. Phys.

156

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Room temperature ionic liquids (RTILs) are solvent with unusual properties, which are difficult to characterize experimentally because of their intrinsic complexity (large number of atoms, strong Coulomb interactions). Molecular simulations have therefore been essential in our understanding of these systems. Depending on the target property and on the necessity to account for fine details of the molecular structure of the ions, a large range of simulation techniques are available. Here I focus on classical molecular dynamics, in which the level of complexity of the simulation, and therefore the computational cost, mostly depends on the force field. Depending on the representation of the ions, these are either classified as all-atom or coarse-grained. In addition, all-atom force fields may account for polarization effects if necessary. The most widely used methods for RTILs are described together with their main achievements and limitations.

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“…It is true that the conductivity is generally lower than one would anticipate in a fully dissociated fluid, but a degree of association of about 50 percent normally suffices to explain the measured values. While it is possible that charge transfer 15,19 can at least offer a partial explanation for these discrepancies, there seems to be little overall consensus about this issue in the presence of seemingly contradictory experimental results.…”

Section: Introductionmentioning

confidence: 88%

“…In future work, fractional charges may also feature, given the possibility that charge transfer may play a role in RTILs. 15,19 In this context, we note that varying the ionic charge is essentially equivalent to changing the dielectric constant or the temperature. In contrast to the standard RPM, for all ions, the charge will be located a distance, b, away from the hard-sphere centres of the particles.…”

Section: Model and Methodsmentioning

confidence: 99%

Ion pairing and phase behaviour of an asymmetric restricted primitive model of ionic liquids

Nordholm

et al. 2016

The Journal of Chemical Physics

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. (2016). Ion pairing and phase behaviour of an asymmetric restricted primitive model of ionic liquids. Journal of Chemical Physics, 145(23), [234510]. https://doi.org/10.1063/1.4972214General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.• Users may download and print one copy of any publication from the public portal for the purpose of private study or research.• You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal Take down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. Ion Pairing and Phase Behaviour of an Asymmetric Restricted Primitive Model of Ionic LiquidsHongduo Lu †1 , Bin Li †1 , Sture Nordholm 2 , Clifford E. Woodward 3 , and Jan formed from ion pairs. The present exploration of the system focuses on the ion pair formation mechanism, the relative concentration of paired and free ions and the consequences for the cohesive energy, and the tendency to form fluid or solid phase. In contrast to studies of similar (though not identical) models in the past, we focus on behaviours at room temperature. By MC and MD simulations of such systems composed of monovalent ions of hard-sphere (or * To whom correspondence should be addressed 1 essentially hard-sphere) diameter equal to 5 Å and a charge displacement from hard-sphere origin ranging from 0 to 2 Å we find that ion pairing dominates for b larger than 1 Å. When b exceeds about 1.5 Å, the system is essentially a liquid of dipolar ion pairs, with a small presence of free ions. We also investigate dielectric behaviours of corresponding liquids, composed of purely dipolar species. Many basic features of ionic liquids appear to be remarkably consistent with those of our ARPM at ambient conditions, when b is around 1 Å. However, the rate of self-diffusion and, to a lesser extent, conductivity are overestimated, presumably due to the simple spherical shape of our ions in the ARPM. The relative simplicity of our ARPM in relation to the rich variety of new mechanisms and properties it introduces, and to the numerical simplicity of its exploration by theory or simulation, makes it an essential step on the way towards representation of the full complexity of ionic liquids.

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On the origin of ionicity in ionic liquids. Ion pairing versus charge transfer

Cited by 205 publications

References 105 publications

En route formation of ion pairs at the ionic liquid–vacuum interface

En route formation of ion pairs at the ionic liquid–vacuum interface

Simulations of room temperature ionic liquids: from polarizable to coarse-grained force fields

Ion pairing and phase behaviour of an asymmetric restricted primitive model of ionic liquids

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