Atomic dipole polarization in charge-transfer complexes with halogen bonding

The polarization effects associated with halogen bonding for the series of charge-transfer complexes D(m)···X-Y, where donor molecules D(m) = NH(3), H(2)O, H(2)S, C(2)H(4), CO and X-Y = Cl(2), ClF, Br(2), BrCl, ICl, I(2), are characterized in terms of the quantum theory of atoms in molecules using the B3LYP/6-311** Kohn-Sham wave functions. We study the electrostatic potential features of separate donor and acceptor molecules, the change in atomic charges as well as the atomic electric dipole moments and their components, and the intra-atomic electron density dipole polarization and the bonding dipole moments resulting from the electron density redistribution between the molecules in the charge-transfer complexes. The equation linking the most negative electrostatic potential values in the donor molecules and the most positive values in dihalogen molecules with the stretching force constants was found using two-factor regression. It is demonstrated that the dipole polarization of the acceptor atom mirrors the strength of halogen bonding in complexes in a series of different donors and acceptors. An exponential relationship between the magnitude of the total atomic electric dipole moment of the acceptor atom and the intermolecular stretching force constant is established for weakly bounded complexes.