Halogen and Chalcogen Bond Energies Evaluated Using Electron Density Properties

Halogen (X-bond) and chalcogen bond (Ch-bond) energies for 36 complexes have been obtained at the RI-MP2/def2-TZVP level of theory, involving the heavier halogen and chalcogen atoms (Br, I, Se, Te). We have explored the existence of linear relationships between the interaction energies and the local kinetic energy densities at the bond critical points that characterize the sigma-hole interactions (both electronic G(r) and potential V(r) energy densities). Interestingly, we have found strong relationships for halogen and chalcogen bonding energies, especially for the V(r) energy density, thus allowing to estimate the interaction energy without computing the separate monomers. This is also useful to estimate the interaction in monomeric systems (intramolecular X/Ch-bonds), as illustrated using several examples. Remarkably, we have also found a good relationship when in the same representation both halogen and chalcogen atoms are included, thus allowing to use the same empirical correlation for both interactions.