Study on the nature of unusual hydrogen-bonded complexes FClHX and halogen-bonded complexes FClClF

Symmetry-adapted perturbation theory (SAPT) analysis has been carried out to understand the nature of the unusual hydrogen-bonded complex FClδ+⋯δ+HX and halogen-bonded complex FClδ+⋯δ+ClF formed by the interactions between two positively charged atoms of different polar molecules. We found that the induction and dispersion contributions play a crucial role in the stabilities of complexes FClδ+⋯δ+HX and FClδ+⋯δ+ClF. The atoms in molecules (AIM) theory, in particular the Laplacian of charge density, ▿2ρ(r), was also applied to explain the nature of all of the complexes. The interaction between two contact positively charged atoms Clδ+⋯δ+H or Clδ+⋯δ+Cl can be viewed as a combination of the nonbonded (lone) charge concentration of Lewis base chlorine atom of ClF with the electron density depletion of other positively charged atom.