Substituent Effects in Multivalent Halogen Bonding Complexes: A Combined Theoretical and Crystallographic Study

Area of Science:

• Computational Chemistry
• Crystallography
• Supramolecular Chemistry

Background:

• Halogen bonding is a key non-covalent interaction.
• Understanding substituent effects is crucial for designing molecular interactions.
• Multivalent halogen bonding involves atoms with multiple bonds to halogen.

Purpose of the Study:

• To investigate the impact of aromatic substitution on charge-assisted multivalent halogen bonding.
• To correlate electronic effects with interaction strength and structural parameters.
• To validate computational findings with experimental crystallographic data.

Main Methods:

• Ab initio calculations (RI-MP2/def2-TZVPD)
• Cambridge Structural Database (CSD) searches
• Hammett's plot analysis
• Atoms in Molecules (AIM) and Natural Bonding Orbital (NBO) analyses

Main Results:

• Aromatic substitution strongly influences halogen bond strength.
• Electron-donating groups (e.g., NH₂, OCH₃) weaken interactions.
• Electron-withdrawing groups (e.g., CN, CF₃) strengthen interactions.
• Direct correlation observed between Hammett's σ parameter, molecular electrostatic potential, and C-I bond extension.
• Computational predictions validated by numerous X-ray structures from the CSD.

Conclusions:

• Aromatic substitution provides a tunable handle for modulating halogen bond strength.
• The study offers a deeper understanding of structure-property relationships in halogen bonding.
• Findings are relevant for crystal engineering and rational design of materials.