jz8b01481_si_liveslides.zip (8.12 MB)
Charge Environment and Hydrogen Bond Dynamics in Binary Ionic Liquid Mixtures: A Computational Study
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posted on 2018-06-22, 19:46 authored by Nikhil
V. S. Avula, Anirban Mondal, Sundaram BalasubramanianThe
extent of charge transfer between the cation and the anion
in a room-temperature ionic liquid depends on the basicity of the
anion. Ion charges determined in the condensed state via density functional
theory calculations capture this effect rather well, and charges derived
in such a manner have been employed in force field-based molecular
dynamics simulations to quantitatively reproduce several physical
properties of the liquids. However, the issue of transferability of
cation charges in mixtures of ionic liquids, say with one type of
cation and two different anion types needs to be addressed. Herein,
we demonstrate that the cation charge in such a mixture varies linearly
with anion composition, a result that ties in rather well with X-ray
photoelectron spectroscopic experiments. The variation in cation charge
with bulk anion composition is shown to be a result of changes in
its coordination environment. Cations surrounded by a higher proportion
of more basic anions possess lower charges than those surrounded by
less basic anions. Time scales for the exchange of anion types for
the occupation of hydrogen bonding sites around the cation have been
determined and are seen to be constituted by three processes–breakage
of existing hydrogen bond, diffusion to the hydrogen bonding site
and displacement of the incumbent anion from its site in the cation
coordination shell. These time scales explain the differences observed
between infrared and NMR spectroscopic experiments in ionic liquid
mixtures rather well.