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Trace Water Effects on Crystalline 1-Ethyl-3-methylimidazolium Acetate
Ashlee Aiello1, John R Hoffman1, Anthony P Kotula1
1National Institute of Standards and Technology, 100 Bureau Drive, Gaithersburg, Maryland 20899, United States.
The Journal of Physical Chemistry. B
|May 16, 2023
Summary
Spontaneous crystallization of 1-ethyl-3-methylimidazolium acetate ionic liquid occurs when trace water is removed. Water
Area of Science:
- Materials Science
- Physical Chemistry
Background:
- 1-ethyl-3-methylimidazolium acetate ([C2mim][OAc]) is a hygroscopic ionic liquid.
- Water content significantly influences ionic liquid properties and structure.
Purpose of the Study:
- To investigate the spontaneous crystallization of [C2mim][OAc] upon water removal.
- To elucidate the molecular mechanisms driving crystallization and decrystallization.
Main Methods:
- Analytical nuclear magnetic resonance spectroscopy for purity assessment.
- Raman spectroscopy and quartz crystal microbalance/infrared spectroscopy for molecular reorganization studies.
- Density functional theory calculations for theoretical insights.
- Two-dimensional wide-angle X-ray scattering for crystal structure confirmation.
Main Results:
- Spontaneous crystallization of [C2mim][OAc] at room temperature was observed upon removal of trace water.
- Water removal induced imidazolium cation ring stacking and side chain clustering.
- Acetate anions exclusively arranged within the cation ring plane.
- Crystallization and decrystallization dynamics were linked to trace water levels.
Conclusions:
- Trace water removal triggers spontaneous crystallization in [C2mim][OAc].
- Water plays a critical molecular-level role in maintaining the liquid structure of hygroscopic ionic liquids.
- Understanding water's role is crucial for controlling ionic liquid behavior and applications.
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