Competitive hydrogen-bonding and halogen-bonding interactions in the dimerization of hypobromous acid (HOBr) molecules

The dimerization of hypobromous acid molecules was investigated using MP2 method with aug-cc-pVTZ basis set. Six different configurations were found as the local minima, corresponding to different dimers with one hydrogen bond or one halogen bond, or cyclic structures formed via simultaneously two hydrogen bonds or two halogen bonds, or one hydrogen bond along with one halogen-bonding-like interaction. These dimers exhibit different binding energies. The dimers with one O–H···O hydrogen bond and the cyclic one with an O–H···O HB and an O–Br···O interaction as well as another one with two O–H···Br hydrogen bonds are much stronger than the dimer with one O–Br···O halogen bond, while the dimer with one O–Br···Br halogen bond is even weaker. The topological property of the hydrogen bond or halogen bond in each dimer was assessed by AIM analysis. NBO analysis was employed to reveal the important roles of the intermolecular donor-acceptor orbital interactions and the charge transfer in each dimer. EDA analyses suggest that the electrostatic, exchange, polarization, and dispersion interactions are the attractive forces in stabilizing the complex, while the Pauli term is the repulsive force.