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From Molecules to Materials: Engineering New Ionic Liquid Crystals Through Halogen Bonding
Published on: March 24, 2018
Structural analysis of [ChCl](m)[ZnCl(2)](n) ionic liquid by X-ray absorption fine structure spectroscopy
Yang Zou1, Hongjie Xu, Guozhong Wu
1Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai, China.
The Journal of Physical Chemistry. B
|January 29, 2009
Summary
This study reveals new insights into the structure of choline chloride-zinc chloride ionic liquids. A novel Cl-Zn-Cl ion pair was identified, significantly impacting the liquid
Area of Science:
- Materials Science
- Physical Chemistry
- Inorganic Chemistry
Background:
- Ionic liquids (ILs) composed of choline chloride (ChCl) and zinc chloride (ZnCl2) are tunable materials with diverse applications.
- Understanding the speciation and structural evolution of these ILs with varying compositions is crucial for optimizing their properties.
Purpose of the Study:
- To investigate the local structures and coordination environments of zinc species in ChCl-ZnCl2 ionic liquids.
- To elucidate the influence of ZnCl2 mole fraction on the anion forms and overall structure.
- To identify novel species and propose interaction mechanisms within the ionic liquid.
Main Methods:
- X-ray absorption fine structure (XAFS) spectroscopy was employed to determine the average coordination number and interatomic distances of Zn species.
- Differential scanning calorimetry (DSC) was used in conjunction with XAFS to analyze thermal properties and phase behavior.
- Analysis of coordination numbers and distances allowed for the determination of Zn species' local structures.
Main Results:
- The mole fraction of ZnCl2 (x(ZnCl2)) systematically influences the coordination number of Zn species.
- Besides known ZnCl3- and Zn2Cl5- anions, a Cl-Zn-Cl ion pair was identified as a major species at higher x(ZnCl2).
- This newly discovered Cl-Zn-Cl ion pair significantly affects the ionic liquid's properties.
Conclusions:
- The speciation in ChCl-ZnCl2 ionic liquids is strongly dependent on the composition.
- The identification of the Cl-Zn-Cl ion pair provides a new understanding of zinc-based ionic liquids.
- A novel interaction mechanism between Ch+ cations and Cl-Zn-Cl ion pairs or Cl- anions was proposed based on structural analysis.
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