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

David Quiñonero,Antonio Frontera

doi:10.3390/inorganics7010009

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.

Highlights

The comprehension of noncovalent forces lays the foundations for the interdisciplinary field of catalysis, supramolecular, biological, and atmospheric chemistry [1]
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−
Comparison of the energetics of the complexes indicates that the only XB complexes that are more favored than the HB ones are HIO:NH3, HIO:Cl−, HIO2 :Cl−, and HXO3 :Cl−

Summary

Introduction

The comprehension of noncovalent forces lays the foundations for the interdisciplinary field of catalysis, supramolecular, biological, and atmospheric chemistry [1]. Apart from hydrogen bonding [3,4,5,6,7], there are other kinds of noncovalent interactions that have been attracting much attention from the scientific community, especially in the last few years, namely tetrel [8,9,10], pnictogen [11], chalcogen [12,13], halogen [14,15], and aerogen [16] bonds. There is a common pattern in all these noncovalent contacts: an interaction between an electron-density-rich region of a molecule, acting as a Lewis base, with an electron-density-deficient region (tetrel, pnictogen, chalcogen, halogen, or aerogen atoms) of another molecule, acting as a Lewis acid, the latter corresponding to a region of lower electron density associated with a portion of the surface electrostatic potential of a system, known as σ-hole. The formation of a covalent bond or bonds causes an anisotropy of the charge distribution of the atom giving rise to these σ-holes [17,18]

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Results

Conclusion