MD Simulations of the Formation of Stable Clusters in Mixtures of Alkaline Salts and Imidazolium-Based Ionic Liquids

Structural and dynamical properties of room-temperature ionic liquids containing the cation 1-butyl-3-methyl­imidazolium ([BMIM]+) and three different anions (hexafluorophosphate, [PF6]−, tetrafluoroborate, [BF4]−, and bis(trifluoro­methyl­sulfonyl)­imide, [NTf2]−) doped with several molar fractions...

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Veröffentlicht in:The journal of physical chemistry. B 2013-03, Vol.117 (11), p.3207-3220
Hauptverfasser: Méndez-Morales, Trinidad, Carrete, Jesús, Bouzón-Capelo, Silvia, Pérez-Rodríguez, Martín, Cabeza, Óscar, Gallego, Luis J, Varela, Luis M
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Sprache:eng
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Zusammenfassung:Structural and dynamical properties of room-temperature ionic liquids containing the cation 1-butyl-3-methyl­imidazolium ([BMIM]+) and three different anions (hexafluorophosphate, [PF6]−, tetrafluoroborate, [BF4]−, and bis(trifluoro­methyl­sulfonyl)­imide, [NTf2]−) doped with several molar fractions of lithium salts with a common anion at 298.15 K and 1 atm were investigated by means of molecular dynamics simulations. The effect of the size of the salt cation was also analyzed by comparing these results with those for mixtures of [BMIM]­[PF6] with NaPF6. Lithium/sodium solvation and ionic mobilities were analyzed via the study of radial distribution functions, coordination numbers, cage autocorrelation functions, mean-square displacements (including the analysis of both ballistic and diffusive regimes), self-diffusion coefficients of all the ionic species, velocity and current autocorrelation functions, and ionic conductivity in all the ionic liquid/salt systems. We found that lithium and sodium cations are strongly coordinated in two different positions with the anion present in the mixture. Moreover, [Li]+ and [Na]+ cations were found to form bonded-like, long-lived aggregates with the anions in their first solvation shell, which act as very stable kinetic entities within which a marked rattling motion of salt ions takes place. With very long MD simulation runs, this phenomenon is proved to be on the basis of the decrease of self-diffusion coefficients and ionic conductivities previously reported in experimental and computational results.
ISSN:1520-6106
1520-5207
DOI:10.1021/jp312669r