New Type of Halogen Bond: Multivalent Halogen Interacting with π- and σ-Electrons.

Sławomir Grabowski

doi:10.3390/molecules22122150

Abstract

MP2/aug-cc-pVTZ calculations were performed for complexes of BrF3 and BrF5 acting as Lewis acids through the bromine centre, with species playing a role of Lewis base: dihydrogen, acetylene, ethylene, and benzene. The molecular hydrogen donates electrons by its σ-bond, while in remaining moieties—in complexes of hydrocarbons; such an electron transfer follows from π-electrons. The complexes are linked by a kind of the halogen bond that is analyzed for the first time in this study, i.e., it is the link between the multivalent halogen and π or σ-electrons. The nature of such a halogen bond is discussed, as well as various dependencies and correlations are presented. Different approaches are applied here, the Quantum Theory of Atoms in Molecules, Natural Bond Orbital method, the decomposition of the energy of interaction, the analysis of electrostatic potentials, etc.

Highlights

The halogen bond is one of the most important interactions that play a crucial role in numerous chemical and biological processes; it is analyzed in experimental and theoretical studies [1,2,3,4].For example, its role in crystal engineering was described, and it was found that it is often competitive with the hydrogen bond [5]
The dual character of halogen atoms may be explained in terms of the σ-hole concept that is applied for the halogen bond [3,4], as well as for other interactions where the centers of groups 14–18 act as Lewis acids in spite that numerous of them are classified as electronegative ones [6,10,11]
BrF3 complexes, complexes,white whitecircles—the circles—theBrF. It seems to be a surprising result that the orbital interaction is often comparable here with the. It seems to be a surprising result that the orbital interaction is often comparable here with the electrostatic interaction; it was found in earlier studies, especially those concerning hydrogen electrostatic interaction; it was found in earlier studies, especially those concerning hydrogen bonds, that in a case of π-electrons playing a role of the Lewis base in complexes, the interaction bonds, that in a case of π-electrons playing a role of the Lewis base in complexes, the interaction energy energy terms related to the electron charge shifts are very important [44,45]

Summary

Introduction

The halogen bond is one of the most important interactions that play a crucial role in numerous chemical and biological processes; it is analyzed in experimental and theoretical studies [1,2,3,4]. The dual character of halogen atoms may be explained in terms of the σ-hole concept that is applied for the halogen bond [3,4], as well as for other interactions where the centers of groups 14–18 act as Lewis acids in spite that numerous of them are classified as electronegative ones [6,10,11] The latter atoms often possess areas of the positive electrostatic potential (EP) since the electron density for A–Z bonds (Z is attributed to tetrel, pnicogen, chalcogen, halogen or aerogen centre) is moved from the Z-centre to the A–Z bond and to other parts of the Lewis acid species. 2150electrostatic potential (EP) distribution [42]

Energetic and Geometric

Nature of Interactions–Decomposition of Interaction Energy

QTAIM Parameters

Electron Charge Density Shifts

Computational

Conclusions