Doubly ionic hydrogen bond interactions within the choline chloride–urea deep eutectic solvent

Abstract

5Deep 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 chlorideurea DES are examined. Evidence is found for a tripodal CH⋅⋅⋅Cl 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 10 of H-bond (OH⋅⋅⋅O=C, NH⋅⋅⋅O=C, OH⋅⋅⋅Cl, NH⋅⋅⋅Cl, OH⋅⋅⋅NH, CH⋅⋅⋅Cl, CH⋅⋅⋅O=C, NH⋅⋅⋅OH and NH⋅⋅⋅NH) 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 Effect of Water upon Deep Eutectic Solvent Nanostructure: An Unusual Transition from Ionic Mixture to Aqueous Solution

“…On average, 50 % of the pure DES nature remains at 10 w (77 mol % water). Whilst weakening of the “DES–DES” interactions (namely the choline–urea, choline–chloride, choline–choline, urea–chloride, urea–urea, and chloride–chloride hydrogen bonds, which may be strong or weak, and nonionic, ionic, or doubly ionic)19 by water is anticipated,20 this deviates significantly from Raoult's ideal entropic dissolution 21. This is corroborated by the DES/water N coord values (namely choline–water, urea–water, and chloride–water interactions), most of which increase as a function of hydration (Figure 2, bottom).…”

“…Therefore, up to 10 w , the system resists hydration to retain most of the initial nanostructure. In this solvation regime, water contributes to the slightly ordered hydrogen‐bonding network in the mixture,19 and is mostly sequestered by choline cations through short‐range Coulombic and hydrogen‐bonding interactions. This explains the tolerance of the DES nanostructure and properties towards hydration, and can be related to the solvophobic accommodation of solutes in ILs;2 “solvent‐separated ion pairs” are seen in many IL/cosolvent mixtures 21.…”

Spectroscopic Evidence for an Attractive Cation–Cation Interaction in Hydroxy‐Functionalized Ionic Liquids: A Hydrogen‐Bonded Chain‐like Trimer

“…[1][2][3][4][5][6][7] Thep roperties of ILs are governed by as ubtle balance of Coulombic interactions,h ydrogen bonding, and dispersion forces. [12,13] This term is apleonasm because ILs consist purely of ions and any hydrogen bonding necessarily takes place between ions. [12,13] This term is apleonasm because ILs consist purely of ions and any hydrogen bonding necessarily takes place between ions.…”

Quantum Chemical Modeling of Hydrogen Bonding in Ionic Liquids

“…Mixtures of two or more ILs, or mixtures of ILs with traditional solvents (such as methanol) can also introduce a more diverse range of H-bonding interactions. This is particularly true of DES [38]. The characteristics of mixtures can be heavily influenced by the H-bonding interactions that take place.…”