Room temperature ionic liquids with two symmetric ions

Room temperature ionic liquids typically contain asymmetric organic cations. The asymmetry is thought to enhance disorder, thereby providing an entropic counter-balance to the strong, enthalpic, ionic interactions, and leading, therefore, to lower melting points. Unfortunately, the synthesis and pur...

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Bibliographic Details
Published in:Chemical science (Cambridge) 2023-09, Vol.14 (37), p.134-1346
Main Authors: Rauber, Daniel, Philippi, Frederik, Schroeder, Daniel, Morgenstern, Bernd, White, Andrew J. P, Jochum, Marlon, Welton, Tom, Kay, Christopher W. M
Format: Article
Language:English
Subjects:
Asymmetry
Cations
Chemistry
Ionic interactions
Ionic liquids
Melting points
Molecular dynamics
Room temperature
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Summary:Room temperature ionic liquids typically contain asymmetric organic cations. The asymmetry is thought to enhance disorder, thereby providing an entropic counter-balance to the strong, enthalpic, ionic interactions, and leading, therefore, to lower melting points. Unfortunately, the synthesis and purification of such asymmetric cations is typically more demanding. Here we introduce novel room temperature ionic liquids in which both cation and anion are formally symmetric. The chemical basis for this unprecedented behaviour is the incorporation of ether-containing side chains - which increase the configurational entropy - in the cation. Molecular dynamics simulations indicate that the ether-containing side chains transiently sample curled configurations. Our results contradict the long-standing paradigm that at least one asymmetric ion is required for ionic liquids to be molten at room temperature, and hence open up new and simpler design pathways for these remarkable materials. Here we present ionic liquids composed of highly symmetric cations and anions. The ionic liquids show competitive physical properties despite the high symmetry. The observed behaviour is rationalised with the concept of configurational entropy.
ISSN:2041-6520
2041-6539
DOI:10.1039/d3sc03240j