2D constraint modifies packing behaviour: a halobenzene monolayer with X₃ halogen-bonding motif

Area of Science:

• Materials Science
• Surface Chemistry
• Crystallography

Background:

• Understanding molecular interactions at surfaces is crucial for materials design.
• 1,3,5-triiodotrifluorobenzene is a molecule with potential for unique surface interactions.
• Crystalline monolayers offer ordered structures for studying fundamental chemical principles.

Purpose of the Study:

• To characterize the crystalline structure of a 1,3,5-triiodotrifluorobenzene monolayer on graphite.
• To investigate the nature and contribution of intermolecular forces within the monolayer.
• To compare experimental findings with theoretical simulations.

Main Methods:

• X-ray diffraction was used to determine the monolayer's crystalline structure.
• Density Functional Theory (DFT) simulations were employed to model the structure and interactions.
• Van der Waals corrections were applied in simulations to accurately assess interaction energies.

Main Results:

• An incommensurate hexagonal unit cell with a lattice parameter of 9.28(7) Å was identified.
• A novel trigonal arrangement of iodine atoms was observed, differing from the bulk structure.
• DFT simulations closely matched experimental data, confirming the structure.

Conclusions:

• Halogen bonding contributes approximately 50% to the total interaction energy in the monolayer.
• Dispersion interactions play a significant role, even in the presence of strong directional non-covalent bonds.
• The study provides insights into the interplay of different forces governing molecular self-assembly on surfaces.