Cl⋅⋅⋅Cl Halogen Bonding: Nature and Effect of Substituent at Electron Donor Cl atom

Abstract Halogen‐halogen bonding plays a vital role in crystal engineering and supramolecular chemistry. The Cl⋅⋅⋅Cl halogen bonding is studied here between R−Cl and ClF molecules using high level quantum chemical methods to find the nature and role of the substituent on the strength of this bond. A wide range of R moieties, like R=Cl, F, CH 3 , C 2 H 5 , C 3 H 7 , (CH 3 ) 3 , H 2 F, CHF 2 , CF 3 , NH 2 , N(CH 3 ) 2 , NHF and NF 2 , are chosen to find the effect of the substituent. The binding energies are found to range between −2.28 and −13.73 kJ mol −1 at the CCSD(T)/aug‐cc‐pVTZ level. The binding energy correlates with the negative electrostatic potential on the Cl atom and IP value of the R−Cl molecules, but it depends upon the nature of R−Cl bond. The electron density [ρ(r c )] at the bond critical point (BCP) is found to be a good parameter to assess the strength of the interaction. The decomposition of interaction energy by using Symmetry Adapted Perturbation Theory (SAPT) reveals that dispersion force is also important in stabilizing the complexes. Several important correlations between the strength of Cl⋅⋅⋅Cl interaction and molecular properties of R−Cl are established.