Pairing of 1-hexyl-3-methylimidazolium and tetrafluoroborate ions in n-pentanol

TL;DR

This study uses molecular dynamics simulations to analyze ion pairing of specific ions in n-pentanol, accurately predicting dissociation constants and revealing complex force dynamics and structural effects.

Contribution

It introduces a molecular model that predicts ion pairing behavior in n-pentanol and highlights limitations of naive dielectric models in capturing structural effects.

Findings

Accurately predicts dissociation constant Kd compared to experiments.

Reveals multiple time-scale effects in ion force autocorrelations.

Identifies dielectric friction effects influencing ion dynamics.

Abstract

Molecular dynamics simulations are obtained and analyzed to study pairing of 1-hexyl-3-methylimidazolium and tetrafluoroborate ions in n-pentanol, in particular by evaluating the potential-of-mean-force between counter ions. The present molecular model and simulation accurately predicts the dissociation constant Kd in comparison to experiment, and thus the behavior and magnitudes for the ion-pair pmf at molecular distances, even though the dielectric constant of the simulated solvent differs from the experimental value by about 30%. A naive dielectric model does not capture molecule structural effects such as multiple conformations and binding geometries of the Hmim+ and BF4- ion-pairs. Mobilities identify multiple time-scale effects in the autocorrelation of the random forces on the ions, and specifically a slow, exponential time-decay of those long-ranged forces associated here with dielectric friction effects.