Halogen-bond geometry: a crystallographic database investigation of dihalogen complexes

Area of Science:

• Crystallography
• Supramolecular Chemistry
• Chemical Bonding

Background:

• Halogen bonding (XB) is a non-covalent interaction analogous to hydrogen bonding (HB).
• Previous studies established XB metrics in the gas phase for simple systems.
• Solid-state structures offer insights into complex interactions with diverse Lewis bases.

Purpose of the Study:

• To investigate the geometric features of halogen-bonded complexes in the solid state.
• To compare solid-state XB parameters with gas-phase data and hydrogen bonding.
• To evaluate the predictive power of a bond-order model for halogen bonds.

Main Methods:

• X-ray crystallography of 141 halogen-bonded complexes.
• Analysis of geometric parameters: Y-X...B angle, X...B distance, and Y-X bond length.
• Correlation analysis between solid-state geometry and solution thermodynamic data.

Main Results:

• Consistent and predictable geometric features were observed for halogen bonds in 141 solid-state complexes.
• The Y-X...B arrangement is more linear than Y-H...B hydrogen bonds.
• A bond-order model accurately predicts the relationship between X...B and Y-X bond length changes.
• Solid-state parameters correlate significantly with solution-phase Lewis acidity/basicity strength.

Conclusions:

• Solid-state halogen bonding exhibits remarkable geometric constancy, supporting gas-phase findings and extending them to new Lewis acids and bases.
• Halogen bonding geometry is predictable and quantifiable, with similarities to hydrogen bonding.
• The study reinforces the understanding of halogen bonding as a significant supramolecular interaction.