Quasi-atomic orbital analysis of halogen bonding interactions

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Chemical Bonding

Background:

• Halogen bonding involves interactions with the electropositive region (σ-hole) of a halogen atom.
• Understanding these interactions is crucial for molecular recognition and crystal engineering.

Purpose of the Study:

• To analyze the electronic properties of ammonia-halogen fluoride (NH3⋯XF) complexes.
• To investigate the nature of σ-hole interactions and N-X bond formation.

Main Methods:

• Quasi-atomic orbital (QAO) analysis was employed.
• Electronic structures of NH3⋯XF complexes (X = F, Cl, Br, I) were calculated.

Main Results:

• Significant electron density transfer from ammonia's nitrogen lone pair to the XF molecule was observed.
• The X-F bond weakens, while the N-X bond gains covalent character as halogen size increases.
• The covalent interaction strength of the N-X bond approaches that in the [NH3X]+ cation.

Conclusions:

• Electron sharing drives the NH3⋯XF interaction, impacting bond strengths.
• The halogen bonding interaction exhibits increasing covalent character with larger halogens.
• These findings provide insights into the electronic basis of halogen bonding.