Comparison between Chlorine-Shared and π-Halogen Bonds Involving Substituted Phosphabenzene and ClF Molecules

Ab initio MP2/aug-cc-pVTZ calculations have been carried out in order to study the nature of P···Cl halogen bonding interaction between a phosphorus atom in an aromatic ring in para-substituted phosphabenzene (PPBZ) and ClF molecule. The interaction of PPBZ with ClF results in two different types of complexes: (i) complex formation through the chlorine-shared halogen bond (T1-X-PPBZ·ClF) and (ii) complex formation via halogen-π interaction (T2-X-PPBZ·ClF). T1-X-PPBZ·ClF complexes are found to be more stable than the T2-X-PPBZ·ClF complexes. This work also presents a general criterion to distinguish a chlorine-shared halogen bond from a traditional halogen bond and sheds light on the formation of the chlorine-shared halogen bond. The binding energy of T1-X-PPBZ·ClF complexes correlates well with the negative electrostatic potential of the P atom and PA value of the substituted PPBZ. The properties of both T1-X-PPBZ·ClF and T2-X-PPBZ·ClF complexes are analyzed using atom-in-molecule, natural bond orbital, and symmetry-adapted perturbation theory calculations. The variation of the Cl-F bond distances and the redshifts of the ν(ClF) vibration resulting from the interaction with PPBZs are discussed.