Exploring non-covalent interactions in binary aromatic complexes

Area of Science:

• Solid-state chemistry
• Supramolecular chemistry
• Materials science

Background:

• Predicting crystal structures with weak interactions is challenging.
• Halogen bonding and π-stacking are key non-covalent interactions in crystal engineering.
• Fluorinated aromatics offer tunable electronic and steric properties.

Purpose of the Study:

• Investigate the effect of halogen substitution on co-crystal formation with p-xylene.
• Characterize the structural evolution from π-stacked to halogen-bonded systems.
• Explore the phase behavior and intermolecular interactions in these co-crystals.

Main Methods:

• Differential scanning calorimetry (DSC) for thermal analysis.
• Variable-temperature powder X-ray diffraction (VT-PXRD) for phase behavior.
• Single-crystal X-ray diffraction (SXD) for detailed structural determination.

Main Results:

• Observed a transition from columnar π-stacked adducts (Cl) to halogen-bonded structures (Br, I).
• Columnar 1:1 adducts showed complex phase behavior due to dipole and steric effects.
• Discrete halogen-π interactions (η², η⁶) were identified with heavier halogens.
• A 1:2 co-crystal with antiferroelectric ordering was formed via halogen bonding.

Conclusions:

• Halogen substitution effectively tunes solid-state architectures and non-covalent interactions.
• Provides insights into weak intermolecular forces for predictive co-crystal design.
• Demonstrates the utility of halogen bonding in creating functional crystalline materials.