Hydrogen Bond versus Halogen Bond in HXOn (X = F, Cl, Br, and I) Complexes with Lewis Bases

Abstract

We have theoretically studied the formation of hydrogen-bonded (HB) and halogen-bonded (XB) complexes of halogen oxoacids (HXOn) with Lewis bases (NH3 and Cl−) at the CCSD(T)/CBS//RIMP2/aug-cc-pVTZ level of theory. Minima structures have been found for all HB and XB systems. Proton transfer is generally observed in complexes with three or four oxygen atoms, namely, HXO4:NH3, HClO3:Cl−, HBrO3:Cl−, and HXO4:Cl−. All XB complexes fall into the category of halogen-shared complexes, except for HClO4:NH3 and HClO4:Cl−, which are traditional ones. The interaction energies generally increase with the number of O atoms. Comparison of the energetics of the complexes indicates that the only XB complexes that are more favored than those of HB are HIO:NH3, HIO:Cl−, HIO2:Cl−, and HIO3:Cl−. The atoms-in-molecules (AIM) theory is used to analyze the complexes and results in good correlations between electron density and its Laplacian values with intermolecular equilibrium distances. The natural bon orbital (NBO) is used to analyze the complexes in terms of charge-transfer energy contributions, which usually increase as the number of O atoms increases. The nature of the interactions has been analyzed using the symmetry-adapted perturbation theory (SAPT) method. The results indicate that the most important energy contribution comes from electrostatics, followed by induction.

Keywords

• hydrogen bond
• halogen bond
• ab initio
• halogen oxoacids