Insights into cation-anion hydrogen bonding in mesogenic ionic liquids: an NMR study
2022 (English)In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 24, no 38, p. 23532-23539Article in journal (Refereed) Published
Abstract [en]
The hydrogen-bonding interaction is studied in imidazolium-based mesogenic ionic liquids in their isotropic, smectic, and solid phases and in a nanoconfined state by proton solid-state nuclear magnetic resonance (NMR). In the smectic phase, the more basic anions form stronger hydrogen bonds. A small decrease of H-bonding in the mesophase with respect to that in the isotropic phase is associated with the presence of a layered assembly with high orientational order and limited conformational freedom. Hydrogen bond strength is not sensitive to the cation structural modification as long as the aprotic nature of the material is preserved. The strong cation-anion hydrogen bonding observed in the smectic phases provides direct support for the presence of ionic sublayers which form in ionic liquid crystals regardless of the location and alignment of the charged group in the cation, particularly irrespective of whether the charged group occupies a terminal or central position in the cation structure. A comparison of the results obtained in isotropic, liquid-crystalline, and solid states shows that in the bulk materials the dynamic state of ions ranging from high reorientational and translational freedom to partial orientation and positional order to full immobilization, respectively, has no strong impact on the cation-anion hydrogen bond strength. On the other hand, nanoconfinement of ionic liquid crystals led to hydrogen bond disruption due to competing interactions of anions with a solid interface.
Place, publisher, year, edition, pages
Royal Society of Chemistry (RSC) , 2022. Vol. 24, no 38, p. 23532-23539
Keywords [en]
Bond strength (materials), Crystal structure, Ionic liquids, Ionic strength, Negative ions, Nuclear magnetic resonance, Phase interfaces, Positive ions, Cation-anions, Charged groups, Hydrogen bond strength, Hydrogen bonding interactions, Imidazolium-based, Ionic liquid crystals, Isotropic phasis, Mesogenics, Nuclear magnetic resonance studies, Smectic phase, Hydrogen bonds
National Category
Physical Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-328123DOI: 10.1039/d2cp03188dISI: 000857436300001PubMedID: 36129074Scopus ID: 2-s2.0-85139342555OAI: oai:DiVA.org:kth-328123DiVA, id: diva2:1762014
Note
QC 20230602
2023-06-022023-06-022023-06-02Bibliographically approved