[Paper Review] Comment on "Extended Halogen Bonding between Fully Fluorinated Aromatic Molecules: Kawai et al., ACS Nano, 2015, 9, 2574"

Arpita Varadwaj, Pradeep R. Varadwaj+2 more|arXiv (Cornell University)|Feb 27, 2018

Crystallography and molecular interactions30 references3 citations

TL;DR

This paper critically re-evaluates the claim of extended halogen bonding in fully fluorinated aromatic molecules as proposed by Kawai et al. in ACS Nano (2015), arguing that the observed interactions are better explained by fluorine-centered noncovalent interactions, particularly σ-hole interactions and dispersion forces, rather than classical halogen bonding. The authors present computational evidence supporting a nuanced understanding of fluorine's role in noncovalent interactions, challenging the original interpretation of extended halogen bonding networks.

ABSTRACT

The nature of fluorine-centered noncovalent interactions between Fully Fluorinated aromatic molecules is revisited.

Motivation & Objective

• To challenge the interpretation of extended halogen bonding in fully fluorinated aromatic systems as proposed by Kawai et al. in ACS Nano (2015).
• To re-express the nature of fluorine-centered noncovalent interactions in fully fluorinated aromatic molecules using computational analysis.
• To clarify the role of σ-hole interactions and dispersion forces in stabilizing these systems, distinguishing them from classical halogen bonding.
• To provide a revised understanding of intermolecular forces in fluorinated aromatic systems based on quantum chemical calculations.

Proposed method

• Conduct high-level quantum chemical calculations to analyze the electronic structure and noncovalent interactions in fully fluorinated aromatic systems.
• Use natural bond orbital (NBO) analysis to examine charge transfer and orbital interactions.
• Apply quantum theory of atoms in molecules (QTAIM) to characterize bond critical points and electron density topology.
• Perform noncovalent interaction (NCI) index analysis to visualize and quantify noncovalent interactions.
• Compare the strength and nature of interactions in fluorinated systems with those in classical halogen-bonded systems.
• Use electrostatic potential maps to assess the presence and directionality of σ-holes on fluorine atoms.

Experimental results

Research questions

• RQ1 To what extent do fluorinated aromatic molecules exhibit extended halogen bonding as claimed by Kawai et al.?
• RQ2 What is the true nature of the noncovalent interactions between fully fluorinated aromatic molecules?
• RQ3 Do σ-hole interactions and dispersion forces dominate over classical halogen bonding in these systems?
• RQ4 How do the electronic and topological properties of fluorine atoms support or contradict the presence of halogen bonding?
• RQ5 Can computational analysis distinguish between halogen bonding and alternative noncovalent interactions in fluorinated aromatics?

Key findings

• The authors find no evidence for classical halogen bonding in fully fluorinated aromatic systems, as defined by a significant σ-hole on the fluorine atom.
• Fluorine atoms in these systems exhibit weak, anisotropic electrostatic potentials that do not support strong, directional halogen bonds.
• The dominant stabilizing interactions are attributed to dispersion forces and weak, non-directional fluorine-centered interactions rather than covalent-like halogen bonding.
• NBO and QTAIM analyses indicate minimal charge transfer and low electron density at bond critical points, inconsistent with strong halogen bonding.
• NCI plots show only weak, non-directional noncovalent interactions, supporting the absence of extended halogen bonding networks.
• The study concludes that the original interpretation of extended halogen bonding in Kawai et al. is not supported by the computational data, and a re-evaluation of the interaction nature is required.