ELECTRON TOPOLOGICAL AND ENERGETIC STUDY OF THE INTERMOLECULAR HALOGEN BONDING INTERACTIONS IN COMPLEXES H2O ••• M (M = F2, ClF, AND CF4)

The halogen bonding complexes H2O center dot center dot center dot M (M = F-2, ClF, and CF4) in comparison with the hydrogen bonding H2O center dot center dot center dot HF complex are studied by high-level ab initio calculations and electron topological atoms-in-molecules (AIM) analyses. The basis set superposition error corrections are important to predict if the structures are in good agreement with the experimental results. Both the CCSD(T)/aug-cc-pVTZ calculations and the AIM analyses indicate a interaction strength order: H2O center dot center dot center dot HF > H2O center dot center dot center dot ClF > H2O center dot center dot center dot F-2 > H2O center dot center dot center dot CF4, with the interaction energies -7.91, -4.16, -1.11, and -1.05 kcal/mol, respectively. The symmetry-adapted perturbation theory analyses have been carried out towards understanding of the nature of the halogen bonding interactions in the complexes H2O center dot center dot center dot M (M = F-2, ClF, and CF4), where the exchange energies are the predominant repulsive components. For the complexes involving polar monomers, the hydrogen bonding H2O center dot center dot center dot HF and the halogen bonding H2O center dot center dot center dot ClF, the largest attractive contributions are the electrostatic energies. However, in H2O center dot center dot center dot F-2 and H2O center dot center dot center dot CF4, the attractive dispersion energies become more important, and the induction energy in the former complex is a little higher than that in the latter. In contrary to the red-shifts of H-F, Cl-F, and F-F bond stretching vibrational frequencies in the complexes H2O center dot center dot center dot M (M = HF, ClF, and F-2), the blue-shifts are predicted for C-F bonds neighboring water in H2O center dot center dot center dot CF4.