F-Halogen Bond: Conditions for Its Existence

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Supramolecular Chemistry

Background:

• The ability of fluorine to participate in halogen bonding (XB) is an area of ongoing scientific debate.
• Understanding XB interactions is crucial for various chemical and biological processes.

Purpose of the Study:

• To computationally investigate the potential for fluorine atoms to form halogen bonds (XB).
• To identify the molecular and electronic factors that influence XB formation involving fluorine.

Main Methods:

• Density functional theory (DFT) calculations were employed.
• A diverse set of organic and inorganic fluorine-containing acids were paired with various Lewis bases.
• Energetic, geometric, and electronic properties were analyzed.

Main Results:

• Perfluorinated hydrocarbons generally do not form XBs with N-bases, though electron-withdrawing substituents can induce weak interactions.
• Inorganic acids like O2NF, FOF, ClF, BrF, SiF4, and GeF4 show limited XB capability, while F2 can form stronger XBs (up to 5 kcal/mol).
• A positive charge on the Lewis acid and an anionic base significantly enhance XB strength. The intensity of the σ-hole (Vs,max ≥ 10-15 kcal/mol) is a key predictor.

Conclusions:

• Fluorine can engage in halogen bonding, but typically requires specific activating features like electron-withdrawing groups or positive charges.
• The study provides a predictive framework for identifying conditions favorable for fluorine-based halogen bonding.
• Observed interactions correlate with geometric criteria and the electronic properties of the σ-hole.