Theoretical Description of R-X⋯NH₃ Halogen Bond Complexes: Effect of the R Group on the Complex Stability and...

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Supramolecular Chemistry

Background:

• Halogen bonding is a significant non-covalent interaction.
• Understanding factors influencing halogen bond strength is crucial for molecular design.
• Previous studies highlight electrostatic contributions, but electron correlation effects also play a role.

Purpose of the Study:

• To theoretically investigate the stability of R-X⋯NH3 halogen bonded systems.
• To analyze the influence of R substituent electronic properties on halogen bond strength.
• To explore cooperative effects in polyhalogenated systems and the role of electron localization.

Main Methods:

• Density Functional Theory (DFT) calculations at the ωB97XD/6-31+G(d,p) level.
• Second-order Møller–Plesset perturbation theory (MP2) calculations for energy refinement.
• Information Theory-based electron localization/delocalization analysis using a C++/CUDA program (KLD).

Main Results:

• Halogen bond stability increases with the electron-withdrawing character of the R substituent and follows the Cl < Br < I trend.
• DFT and MP2 binding energies show excellent correlation, validating the dispersion-corrected functional.
• Electron localization analysis reveals sigma-hole depletion influenced by R groups and significant R-X bond polarization due to NH3.

Conclusions:

• Electrostatics is the dominant factor in stabilizing halogen bonds.
• Electron correlation also contributes significantly, particularly in polyhalogenated systems.
• The study provides a comprehensive understanding of halogen bond interactions and their influencing factors.