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Doubly Ionic Hydrogen Bond Interactions Within the Choline Chloride - Urea Deep Eutectic Solvent

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Title: Doubly Ionic Hydrogen Bond Interactions Within the Choline Chloride - Urea Deep Eutectic Solvent
Authors: Hunt, PA
Ashworth, C
Matthews, R
Welton, T
Item Type: Journal Article
Abstract: Deep eutectic solvents (DESs) are exemplars of systems with the ability to form neutral, ionic and doubly ionic H-bonds. Herein, the pairwise interactions of the constituent components of the choline chloride-urea DES are examined. Evidence is found for a tripodal CHCl doubly ionic H-bond motif. Moreover it is found that the covalency of doubly ionic H-bonds can be greater than, or comparable with, neutral and ionic examples. In contrast to many traditional solvents, an alphabet soup of many different types of H-bond (OHO[double bond, length as m-dash]C, NHO[double bond, length as m-dash]C, OHCl, NHCl, OHNH, CHCl, CHO[double bond, length as m-dash]C, NHOH and NHNH) can form. These H-bonds exhibit substantial flexibility in terms of number and strength. It is anticipated that H-bonding will have a significant impact on the entropy of the system and thus could play an important role in the formation of the eutectic. The 2 : 1 urea : choline-chloride eutectic point of this DES is often associated with the formation of a [Cl(urea)2](-) complexed anion. However, urea is found to form a H-bonded urea[choline](+) complexed cation that is energetically competitive with [Cl(urea)2](-). The negative charge on [Cl(urea)2](-) is found to remain localised on the chloride, moreover, the urea[choline](+) complexed cation forms the strongest H-bond studied here. Thus, there is potential to consider a urea[choline](+)·urea[Cl](-) interaction.
Issue Date: 22-Jun-2016
Date of Acceptance: 15-Jun-2016
URI: http://hdl.handle.net/10044/1/33922
DOI: http://dx.doi.org/10.1039/C6CP02815B
ISSN: 1463-9084
Publisher: Royal Society of Chemistry
Start Page: 18145
End Page: 18160
Journal / Book Title: Physical Chemistry Chemical Physics
Volume: 18
Issue: 27
Copyright Statement: This journal is © Royal Society of Chemistry 2016
Sponsor/Funder: Technological Resources PTY Ltd
Funder's Grant Number: 3101488649
Keywords: Chemical Physics
02 Physical Sciences
03 Chemical Sciences
Publication Status: Published
Appears in Collections:Chemistry
Catalysis and Advanced Materials
Faculty of Natural Sciences