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Dynamics, cation conformation and rotamers in guanidinium ionic liquids with ether groups

  • Ionic liquids are modern materials with a broad range of applications, including electrochemical devices, the exploitation of sustainable resources and chemical processing. Expanding the chemical space to include novel ion classes allows for the elucidation of novel structure-property relationships and fine tuning for specific applications. We prepared a set of ionic liquids based on the sparsely investigated pentamethyl guanidinium cation with a 2-ethoxy-ethyl side chain in combination with a series of frequently used anions. The resulting properties are compared to a cation with a pentyl side chain lacking ether functionalization. We measured the thermal transitions and transport properties to estimate the performance and trends of this cation class. The samples with imide-type anions form liquids at ambient temperature, and show good transport properties, comparable to imidazolium or ammonium ionic liquids. Despite the dynamics being significantly accelerated, ether functionalization of the cation favors the formation of crystalline solids. Single crystal structure analysis, ab initio calculations and variable temperature nuclear magnetic resonance measurements (VT-NMR) revealed that cation conformations for the ether- and alkyl-chain-substituted are different in both the solid and liquid states. While ether containing cations adopt compact, curled structures, those with pentyl side chains are linear. The Eyring plot revealed that the curled conformation is accompanied by a higher activation energy for rotation around the carbon-nitrogen bonds, due to the coordination of the ether chain as observed by VT-NMR.

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Document Type:Article
Author:Daniel RauberORCiD, Frederik PhilippiORCiD, Bernd MorgensternORCiD, Josef ZappORCiD, Björn KuttichORCiD, Tobias KrausORCiD, Tom WeltonORCiD, Rolf HempelmannORCiD, Christopher W. M. KayORCiD
Parent Title (English):Journal of ionic liquids
First Page:100060
Year of first Publication:2023
Release Date:2023/07/21
Tag:conformation; dynamics; ionic liquid; nuclear magnetic resonance; structure-property relation
Funding Information:DFG (project number 4772985087); DFG (project number INST 256/506-1)
DDC classes:500 Naturwissenschaften und Mathematik / 540 Chemie
Open Access:Open Access
Signature:INM 2023/082
Licence (German):License LogoCreative Commons - CC BY - Namensnennung 4.0 International