New insights from domain-averaged Fermi holes and bond order analysis into the bonding conundrum in C₂

ABSTRACT

The bonding in the ground state of C₂ is examined using a combined approach based on the analysis of domain-averaged Fermi holes and of the contributions to covalent bond orders that can be associated with individual localised natural orbitals. The σ system in this molecule turns out to be particularly sensitive, evolving from a description that includes a fairly traditional shared electron pair σ bond, for a range of intermediate nuclear separations, to a somewhat different situation near equilibrium geometry, where non-classical repulsive interactions are particularly important. The various results provide further support for the view that the electronic structure of this molecule sufficiently exceeds the scope of traditional bonding paradigms that attempts to classify the bonding in terms of a classical bond multiplicity are highly questionable.

GRAPHICAL ABSTRACT

KEYWORDS:

• Peculiarity of C₂ bonding
• domain-averaged Fermi holes (DAFH)
• localised natural orbitals
• Cioslowski covalent bond order (CBO)
• Wiberg–Mayer index
• quantum theory of atoms in molecules (QTAIM)

Acknowledgement

We thank Gernot Frenking (Philipps-Universität Marburg) for helpful comments and for sending us a preprint of Ref. 17.

Supplemental data for this article can be accessed http://dx.doi.org/10.1080/10.1080/00268976.2015.1112925

Disclosure statement

No potential conflict of interest was reported by the authors.