Refined SMD Parameters for Bromine and Iodine Accurately Model Halogen-Bonding Interactions in Solution

Area of Science:

• Computational Chemistry
• Physical Chemistry
• Quantum Chemistry

Background:

• Accurate calculation of liquid-phase free energies is crucial for understanding chemical species and equilibria.
• Halogen bonding, a significant non-covalent interaction, requires precise computational models for its study.
• Existing solvation models needed refinement for accurate prediction of halogen bonding involving bromine and iodine.

Purpose of the Study:

• To optimize Coulomb radii for bromine (Br) and iodine (I) within the SMD universal solvation model.
• To develop and validate a new computational model (SMD18) for calculating free energies of solvation and halogen bonding.
• To compare the strength of halogen bonding with hydrogen bonding and re-evaluate experimental interpretations.

Main Methods:

• Utilized recent experimental data to optimize new Coulomb radii for Br and I.
• Employed the SMD (Solvation Model based on Density) universal solvation model.
• Validated the optimized SMD18 model against independent experimental data for ionic equilibria involving halogen bonding.

Main Results:

• Successfully optimized Coulomb radii for Br and I, leading to the SMD18 model.
• SMD18 demonstrated satisfactory agreement between theoretical predictions and experimental standard-state free energies for 18 ionic equilibria.
• The model enables a quantitative comparison between hydrogen bonding and halogen bonding.

Conclusions:

• The SMD18 model provides a reliable method for calculating free energies of solvation involving Br and I.
• The optimized parameters enhance the accuracy of computational studies on halogen bonding.
• This work facilitates a deeper understanding of halogen bonding and its comparison to hydrogen bonding in chemical systems.