Linking the the thermal and electronic properties of functional dicationic salts with their molecular structures

Clarke, Coby J.; Morgan, Patrick J.; Hallett, Jason P.; Licence, Peter

Abstract

The two major properties that underpin ionic liquids are tunability and the potential to create task-specific media. Together, these properties allow ionic liquids to surpass the roles long held by traditional molecular solvents. However, at elevated temperatures or under prolonged heating, the structural components that impart such properties decompose or degrade. Dicationic pyridine salts present new opportunities to extend functionality and tunability to high temperatures because they are coordinating and thermally robust. In this work, we present three structurally related series of dicationic pyridine salts, which have been characterized by a wide array of techniques to link thermal and electronic properties to structural variation. The phase transitions and thermal stabilities of the salts were significantly influenced by small structural changes, and several new candidates for high-temperature-based applications were identified. The electron density, and therefore the electron donating ability, of the pyridine functional group could also be controlled by structural variation of cations and anions. Therefore, dicationic pyridine salts are highly tunable choices for task-specific solvents at elevated temperatures. Importantly, thermally robust solvents not only extend operational ranges but also reduce the need to replace or replenish solvents that degrade over time at temperatures commonly employed in industrial settings (i.e., 150−200 °C); solvent lifetimes are extended, and production is reduced. This is a critical requirement for complex media such as ionic liquids, which have high economic and environmental production costs.

• Journal Article Type: Article
• Acceptance Date: Apr 15, 2021
• Online Publication Date: Apr 27, 2021
• Publication Date: May 10, 2021
• Deposit Date: Jun 24, 2021
• Publicly Available Date: Apr 28, 2022
• Journal: ACS Sustainable Chemistry and Engineering
• Electronic ISSN: 2168-0485
• Publisher: American Chemical Society
• Peer Reviewed: Peer Reviewed
• Volume: 9
• Issue: 18
• Pages: 6224-6234
• DOI: https://doi.org/10.1021/acssuschemeng.0c08564
• Public URL: https://nottingham-repository.worktribe.com/output/5504778
• Publisher URL: https://pubs.acs.org/doi/10.1021/acssuschemeng.0c08564
• Additional Information: This document is the Accepted Manuscript version of a Published Work that appeared in final form in ACS Sustainable Chemistry and Engineering, copyright © 2021 American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://pubs.acs.org/doi/10.1021/acssuschemeng.0c08564