Single-electron halogen bond: Ab initio study

Ab initio calculations have been performed on single-electron halogen bonds between methyl radical and bromine-containing molecules to gain a deeper insight into the nature of such noncovalent interactions. Bader's atoms in molecules (AIM) theory have also been applied to the analysis of the linking of the single-electron halogen bond. Various characteristics of the R-Br⋯CH₃ interaction, i.e., binding energies, geometrical parameters and topological properties of the electron density have been determined. The presence of the bond critical points (BCPs) between the bromine atom and methyl radical and the values of electron density and Laplacian of electron density at these BCPs indicate the closed-shell interactions in the complexes. The single-electron halogen bonds, which are significantly weaker than the normal halogen bonds, exhibit equally bond strength as compared to the single-electron hydrogen bond. It has been also found that plotting of the binding energies versus topological properties of the electron density at the BCPs gives two straight lines.