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Updated: Jul 19, 2025
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From Molecules to Materials: Engineering New Ionic Liquid Crystals Through Halogen Bonding
Published on: March 24, 2018
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Modulation of Rotational Dynamics in Halogen-Bonded Cocrystalline Solids
Shubha S Gunaga1, David L Bryce1
1Department of Chemistry and Biomolecular Sciences, Centre for Catalysis Research and Innovation, and Nexus for Quantum Technologies, University of Ottawa, 10 Marie Curie Private, Ottawa, Ontario K1N 6N5 Canada.
Journal of the American Chemical Society
|August 16, 2023
Summary
This study shows how halogen bonds can control methyl group rotation in crystals. By designing cocrystals, researchers can tune molecular dynamics for materials science applications.
Area of Science:
- Solid-state chemistry
- Supramolecular chemistry
- Materials science
Background:
- Molecular dynamics are crucial for material, biomolecule, and catalyst functionality.
- Noncovalent interactions, particularly halogen bonds (XB), offer a route to control these dynamics.
Purpose of the Study:
- To systematically investigate the modulation of methyl group rotational dynamics using halogen bonds.
- To design and prepare novel cocrystalline architectures featuring halogen bonds with tetramethylpyrazine (TMP).
Main Methods:
- Cocrystal preparation using gas-phase, solution, and solid-state mechanochemical methods.
- Single-crystal X-ray diffraction for structural analysis.
- Variable-temperature deuterium solid-state Nuclear Magnetic Resonance (NMR) spectroscopy to measure methyl rotational barriers (Ea).
Main Results:
- Halogen bonds, including those from bromine and weak chlorine donors, act as robust structure-directing elements.
- Methyl rotational barriers (Ea) in tetramethylpyrazine cocrystals ranged from 3.75 to 7.08 kJ mol⁻¹.
- Steric factors (carbon-carbon close contacts) and electronic factors (sigma-hole strength) govern the observed dynamics.
Conclusions:
- Designer cocrystals offer a strategy to modulate molecular dynamics by controlling stoichiometry and close contacts.
- These principles can be applied to tune dynamics in more complex molecular systems and functional groups.
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