A-X⋯σ Interactions-Halogen Bonds with σ-Electrons as the Lewis Base Centre.

Sławomir J Grabowski

doi:10.3390/molecules26175175

Abstract

CCSD(T)/aug-cc-pVTZ//ωB97XD/aug-cc-pVTZ calculations were performed for halogen-bonded complexes. Here, the molecular hydrogen, cyclopropane, cyclobutane and cyclopentane act as Lewis base units that interact through the electrons of the H–H or C–C σ-bond. The FCCH, ClCCH, BrCCH and ICCH species, as well as the F2, Cl2, Br2 and I2 molecular halogens, act as Lewis acid units in these complexes, interacting through the σ-hole localised at the halogen centre. The Quantum Theory of Atoms in Molecules (QTAIM), the Natural Bond Orbital (NBO) and the Energy Decomposition Analysis (EDA) approaches were applied to analyse these aforementioned complexes. These complexes may be classified as linked by A–X···σ halogen bonds, where A = C, X (halogen). However, distinct properties of these halogen bonds are observed that depend partly on the kind of electron donor: dihydrogen, cyclopropane, or another cycloalkane. Examples of similar interactions that occur in crystals are presented; Cambridge Structural Database (CSD) searches were carried out to find species linked by the A–X···σ halogen bonds.

Highlights

Euskal Herriko Unibertsitatea UPV/EHU & Donostia International Physics Center (DIPC) PK 1072, IKERBASQUE, Basque Foundation for Science, 48011 Bilbao, Spain
Examples of similar interactions that occur in crystals are presented; Cambridge Structural Database (CSD) searches were carried out to find species linked by the A–X···σ halogen bonds
Searches through the Cambridge Structural Database, CSD [41,42] (February, 2021 release), were performed to find crystal structures containing a halogen centre in contact with the σ-bond that plays a role in the Lewis base site

Summary

Introduction

Euskal Herriko Unibertsitatea UPV/EHU & Donostia International Physics Center (DIPC) PK 1072, IKERBASQUE, Basque Foundation for Science, 48011 Bilbao, Spain. Studies proposed the idea of a direction-dependent van der Waals radius [15] It was explained in more recent studies that for a carbon–halogen bond, C–X, ellipsoidal-shaped electron charge distribution around halogen centre often occurs [14,16]. The longest semi-axis of this ellipsoid is approximately perpendicular to the C–X bond, whereas the shortest semi-axis is consistent with the direction of this bond This explains why halogen centres are often characterised by a dual role. They can act as Lewis acids in the extension of C–X bonds and they can act as Lewis bases in the directions approximately perpendicular to these bonds [17]. It has been described in several studies that sometimes other bonds,

Objectives

Results

Conclusion