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

Motivated by the need to calculate liquid‐phase free energies of species and equilibria involving halogen bonding, recent experimental data were used to optimize new Coulomb radii for Br and I for use in the SMD universal solvation model for calculating free energies of solvation. The use of the SMD model with these parameters for Br and I and the SMD values of all other parameters is called SMD18. After parametrization, the SMD18 model was tested for data not used in the parametrization. These data are standard‐state free energies (equivalent to equilibrium constants) for 18 ionic equilibria involving Cl, Br, and I halogen bonding in acetonitrile, and the agreement of theory and experiment is satisfactory. The SMD18 model is then used to compare hydrogen bonding to halogen bonding and to reassess the interpretation of recent experiments. Experimental data on halogen bonded complexes has been used to reoptimize the iodine and bromine radius in the SMD intrinsic solvation model. Subsequent testing of this new SMD18 model on several ionic equilibria provided very good agreement between experiment and theory.