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Updated: Jul 12, 2025

From Molecules to Materials: Engineering New Ionic Liquid Crystals Through Halogen Bonding
Published on: March 24, 2018
Ion Mobility in Hydroxy-Functionalized Ionic Liquids Depends on Cationic Clustering: Tracking the Alkyl Chain Length
Alexander E Khudozhitkov1,2, Alexander G Stepanov1, Daniil I Kolokolov1,2
1Boreskov Institute of Catalysis, Siberian Branch of Russian Academy of Sciences, Prospekt Akademika Lavrentieva 5, Novosibirsk 630090, Russia.
Abstract:
Observing and quantifying the like-charge attraction in liquids and solutions is still challenging. However, we showed that elusive cation-cation hydrogen bonding may govern the structure and interaction in hydroxyl-functionalized ionic liquids. Therefore, cationic cluster formation depends on the shape, charge distribution, and functionality of the ions. We demonstrated by means of solid-state 2H NMR spectroscopy that cationic clusters change the structure and dynamics of ionic liquids. With increasing alkyl chain length, we observed two deuteron quadrupole coupling constants for the OD groups, differing by about 30 kHz. The lower value was assigned to the cation-cation interaction, indicating that the average (c-c) hydrogen bonds are stronger than the (c-a) hydrogen bonds between the cation and the anion despite the repulsive and attractive Coulomb interaction in the first and latter cases. Ion mobility could be studied by 2H NMR spectroscopy, although the deuterons in the hydrogen-bonded clusters underwent fast exchange. Our results also showed that simple relaxation models are not applicable anymore and that anisotropic motion must be considered.
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