The Effect of the Substituent's Nature on the Crystallographic and Quantum-Chemical Profile of the Fluorine-Fluorine Interaction.

The investigation of the intermolecular profile of F···F interactions is based on the statistical analysis of data obtained from the Cambridge Structural Database, quantum theory of atoms in molecules, and quantum-mechanical calculations. The influence of the nature of the substituents bound to the interacting fluorine atoms is also investigated. The geometric parameters used to define F···F interactions (bond length, bond angle, and torsion angle) indicate the suitability of F···F interactions for a supramolecular compromise with other interactions from the environment. Regardless of the nature of the substituent, the antiparallel orientation of the interacting groups and long distances (longer than 2.9 Å) represent the specificity of these interactions, which makes them suitable for forming a large number of simultaneous interactions with species from the environment. The shallow minima in the energy profiles, in the range from 3.0 to 3.5 Å, indicate weak noncovalent interactions, as well as the possibility of F···F interactions to easily adapt to the geometries of the surrounding interactions. Changes in the geometry and in the substituents on the aromatic ring have a significantly greater influence on the strength of F···F interactions compared to the case where the interacting fluorine atoms are bound to alkyl groups.