Complex Structural and Dynamical Interplay of Cyano-Based Ionic Liquids
H Weber and B Kirchner, JOURNAL OF PHYSICAL CHEMISTRY B, 120, 2471-2483 (2016).
We carried out ab initio molecular dynamics simulations for the three cyano-based ionic liquids, 1-ethyl-3-methylimidazolium tetracyanoborate (C(2)C(1)ImB(CN)(4)), 1-ethyl-3-methyl-imidazolium dicyanamide (C(2)C(1)ImN-(CN)(2)), and 1-ethyl-3-methylimidazolium thiocyanate (C(2)C(1)ImSCN). We found that the SCN-based ionic liquid is much more prone to pi-pi stacking interactions as opposed to the other two ionic liquids, contrary to the fact that all liquids bear the same cation. Hydrogen bonding is strong in the dicyanamide- and the thiocyanate-based ionic liquids and it is almost absent in the tetracyanoborate liquid. The anion prefers to stay on-top of the imidazolium ring with the highest priority for the N(CN)(2)(-) anion followed by the B(CN)(4)anion. We find that experimental viscosity trends cannot be correlated to the hydrogen bond dynamics which is fastest for B(CN)(4)(-) followed by SCN(-) and N(CN)2(-). For the dynamics of :the cation on-top of itself, we find the order of B(CN)(4)(-) followed by N(CN)(2)(-) and finally by SCN(-). Interestingly, this trend correlates well with the viscosity, suggesting a relation between the cation cation dynamics and the viscosity at least for these cyano-based ionic liquids. These findings, especially, the apparent correlation between cation cation dynamics and the viscosity, might be useful for the suggestion of better ionic liquids in electrolyte applications.
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