Supramolecular Perspective of Coordination Effects on Fluorine Interactions

Coordination effects have been considered through the most common interactions in the crystal structures of fluoro compounds (C-H/F and F/F interactions). The supramolecular profile of these effects is based on quantum-chemical calculations for the assessment of the interaction strength and electrostatic potential maps, which provide a qualitative insight into the examined effect. Coordination of aliphatic fluorides leads to an increase of the negative potential of the F atoms, and, hence, an increase in the hydrogen-bonding acceptor ability (strengthening of C-H/F interactions) and a weakening of the F/F interactions, due to an increase in repulsive interactions between the F atoms. There is no significant change in the potential of the F atoms due to coordination of C-6-aromatic fluorides, as in the case of aliphatic ones. This results in slight changes in the strengths of the C-H/F and F/F interactions (coupled with parallel interaction at large offsets, PILO), in a noticeable enhancement of stacking interactions, as well as in a significant enhancement of interactions involving the pi-system (F/pi - and C-H/pi interactions). It has also been shown that a decrease in the charge of the metal ions leads to a decrease in the negative potential of the F atom and also that the nature of the metal ion has a significant influence on the value of the potential of the F atoms.