Reply to: An approach to the resolution of the dispute on collective atomic interactions

Nuno A. G. Bandeira, a theoretical chemist at the BioISI Research Centre of the Faculty of Sciences of ULisboa (CIÊNCIAS), recently published a paper in the journal Nature Communications on the nature and energetics of the chemical bond in an ionic molecule. The team included two other researchers in theoretical chemistry: Cina Foroutan-Nejad, from Warsaw (Institute of Physical Chemistry of the Polish Academy of Sciences), and Ángel Martín-Pendás, from Spain (University of Oviedo).

The discovery, in 2022, that the LiCF₃ molecule [(trifluoromethyl)lithium] did not have the expected tetrahedral arrangement took researchers by surprise. A computational analysis revealed that this geometry is not the most energetically stable, but rather one in which the position of the lithium cation is inverted (Figure 1).

Chemists are used to thinking of unpaired electrons that bear a negative charge as the preferential targets of any electron-poor species (e.g. a cation). With trifluoromethanide (CF₃^-), the cation prefers to be closer to the fluorine atoms, in spite of the negative charge being formally located on the carbon atom. This new type of chemical bond has been named 'collective bond', because all the atoms (even the distant carbon) contribute to the creation of the bond with the lithium ion. The metrics used showed that the negative charge is sufficiently delocalised for all the atoms to contribute to the bond leading to the whole being greater than the sum of its parts.

This new classification led to some controversy. In 2023, a group of different authors published a paper in which, using an alternative computational methodology, they challenged the use of this new designation and the original interpretation of the chemical bonding mode. In any case, it was confirmed that the donor-acceptor interaction was stronger with fluorine atoms.

This article now reaffirms the designation of ‘collective bonding’, using additional computational tools to support the original claim.

Nuno A. G. Bandeira explains: ‘Any worthwhile theoretical methods with computational applicability have to describe the chemical bond of any molecule in the same way. The idea we followed was to use a very high-quality molecular wave function and to dissect the various electronic donation channels as well as the range of contributions to their energy. Given that the molecule is so small and light, this calculation can even be done on a laptop, without the need for a large computing centre’.

This finding adds to our knowledge of this type of ionic molecules within the scope of the Lewis acid-base concept. A detailed knowledge of these features will contribute to the rational development of new materials.

History:

1st paper https://www.nature.com/articles/s41467-022-29504-0

2nd paper https://www.nature.com/articles/s41467-023-39498-y

3rd paper https://www.nature.com/articles/s41467-024-54552-z

4th paper, replying to the previous one https://www.nature.com/articles/s41467-024-54553-y