Halogen Bonding versus Hydrogen Bonding: A Molecular Orbital Perspective.

Area of Science:

• Computational Chemistry
• Chemical Physics
• Quantum Chemistry

Background:

• Hydrogen bonds are well-understood intermolecular interactions.
• Halogen bonds (DX···A⁻) are analogous to hydrogen bonds (DH···A⁻).
• Understanding halogen bonds is crucial for various chemical and biological systems.

Purpose of the Study:

• To computationally analyze the structure and bonding mechanisms of trihalides and analogous hydrogen-bonded complexes.
• To establish consistent data for inferring trends in halogen bond structure and stability.
• To elucidate the nature of halogen bonds and compare them with hydrogen bonds.

Main Methods:

• Relativistic density functional theory (DFT) calculations using zeroth-order regular approximation (ZORA-BP86/TZ2P).
• Quantitative Kohn-Sham molecular orbital (MO) theory.
• Energy decomposition analyses (EDA) and Voronoi deformation density (VDD) analyses.

Main Results:

• Halogen bonds involve classical electrostatic attraction.
• Significant stabilization arises from interactions between the lone pair of the anion (A⁻) and the σ* orbital of the D-X bond.
• Consistent data on structure and stability trends were obtained across a range of systems.

Conclusions:

• A detailed physical model of the halogen bond is presented.
• Halogen bonds share similarities with hydrogen bonds but possess unique characteristics.
• The study enhances the understanding of halogen bonding through advanced computational methods.