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Updated: May 31, 2026
06:44
From Molecules to Materials: Engineering New Ionic Liquid Crystals Through Halogen Bonding
Published on: March 24, 2018
Molecular-network-ionic structure transitions in liquid AlCl(3) and ZnCl(2) halogenides under pressure
V V Brazhkin1, A G Lyapin, S V Popova
1Institute for High Pressure Physics, Russian Academy of Sciences, Troitsk, Moscow region, 142190, Russia.
Summary
High pressure transforms pseudo-covalent liquid aluminum chloride (AlCl3) and zinc chloride (ZnCl2) from a molecular network to an ionic structure. This two-stage structural change under compression is common in simple melts.
Area of Science:
- Materials Science
- Condensed Matter Physics
- High-Pressure Chemistry
Background:
- Liquid aluminum chloride (AlCl3) and zinc chloride (ZnCl2) exhibit quasi-molecular network structures at ambient conditions.
- These melts represent an intermediate state between purely covalent and ionic liquids.
- Understanding their structural behavior under pressure is crucial for materials science and geochemistry.
Purpose of the Study:
- To investigate the in situ structural transformations of liquid AlCl3 and ZnCl2 under high pressure and temperature.
- To elucidate the pressure-induced changes from a molecular-network to an ionic structure.
- To identify the pressure ranges for these structural transitions.
Main Methods:
- In situ high-pressure, high-temperature X-ray diffraction studies were performed on liquid AlCl3 and ZnCl2.
- Analysis focused on changes in intermediate-range and short-range order as a function of pressure.
- Structural models were compared to understand the evolution of bonding and network structure.
Main Results:
- A rapid breakdown of the tetrahedral network's intermediate-range order was observed up to 2.5 GPa for AlCl3 and 1.8 GPa for ZnCl2.
- Sharp transitions to short-range order, resembling ionic melt structures, occurred around 4 GPa for AlCl3 and 3 GPa for ZnCl2.
- A two-stage structural transformation was identified: gradual decay of network correlations followed by a sharp transition to ionic structure.
Conclusions:
- Pseudo-covalent liquid halogenides like AlCl3 and ZnCl2 undergo significant structural changes under compression.
- The observed two-stage transformation (network decay to ionic structure) is a general phenomenon in simple melts under pressure.
- These findings provide insights into the behavior of melts under extreme conditions, relevant to various scientific disciplines.
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