Possible dimers of hypochlorous acid (HOCl) arising from hydrogen- and halogen-bond interactions

The possible hypochlorous acid dimers with six different configurations were found which were investigated by means of ab initio method at the MP2/aug-cc-pVTZ computational level. They were identified to be local minima, corresponding to two dimers with one O-H center dot center dot center dot O hydrogen bond, one dimer with one O-Cl center dot center dot center dot O halogen bond, one cyclic dimer with one O-H center dot center dot center dot Cl hydrogen bond and one O-Cl center dot center dot center dot Cl. halogen bond, one cyclic dimer with two hydrogen bonds, and one dimer with one O-Cl center dot center dot center dot Cl halogen bond. Their optimized geometries, stretching vibrational frequencies and interaction energies have been obtained and analyzed. The results show that the dimers with one O-H center dot center dot center dot O hydrogen bond and the cyclic one with two O-H center dot center dot center dot Cl hydrogen bonds are much stronger than the dimer with one O-Cl center dot center dot center dot O halogen bond, while the dimer with one O-O center dot center dot center dot Cl halogen bond is even weaker. AIM analysis was performed to examine the topological property of the hydrogen bond or halogen bond in the complex. The important roles of the intermolecular donor-acceptor orbital interactions as well as the charge transfer in these complexes were demonstrated by NBO analysis. Energy decomposition analyses indicate that the electrostatic, orbital and dispersion terms are the attractive interactions contributing to the stability of the complex, whereas the Pauli term is the repulsive interaction. (C) 2012 Elsevier B.V. All rights reserved.