Very strong chalcogen bonding: Is oxygen in molecules capable of forming
it? A First-Principles Perspective
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 here 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-1) to the ultra-strong (–90.10 kcal mol-1). 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]– (~ 40
kcal mol-1). 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 an n (lone-pair bonding orbital) -> σ*
(anti-bonding orbital) 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.