Very strong chalcogen bonding: Is oxygen in molecules capable of forming it? A First Principles Perspective

TL;DR

This study demonstrates that oxygen atoms in molecules can form strong chalcogen bonds, challenging previous beliefs that such bonds are weak or impossible, with energies comparable to hydrogen bonds.

Contribution

The paper provides first-principles evidence that oxygen can act as a strong chalcogen bond donor, revealing new insights into noncovalent interactions involving oxygen.

Findings

Oxygen can form chalcogen bonds with energies up to -90 kcal/mol.

Many interactions involve mixed ionic and covalent character.

Bonding involves charge transfer and orbital delocalization.

Abstract

There are views prevalent in the noncovalent chemistry literature that i) the O atom in molecules cannot form a chalcogen bond, and ii) if formed, this bond is very weak. We have shown in this study that these views are not necessarily true since the attractive energy between the oxygen atom of some molecules and several electron rich anionic bases examined in a series of 34 ion-molecule complexes varied from the weak (ca -2.30 kcal/mol) to the ultrastrong (-90.10 kcal/mol). The [MP2/aug-cc-pVTZ] binding energies for several of these complexes were found to be comparable to or significantly larger than that of the well-known hydrogen bond complex [FH...F]- (roughly -40 kcal/mol). The nature of the intermolecular interactions was examined using the quantum theory of atoms in molecules, second order natural bond orbital and symmetric adaptive perturbation theory energy decomposition analyses. It was found that many of these interactions comprise mixed bonding character (ionic and covalent), especially manifest in the moderate to strongly bound complexes. All these can be explained by a bonding to an anti-bonding orbital type donor acceptor charge transfer delocalization. This study, therefore, demonstrates that the covalently bound oxygen atom in molecules can have a significant ability to act as an unusually strong chalcogen bond donor.