Fluoride Anions: Unexploited but Effective Halogen Bond Acceptors.

Due to their high electron density, fluoride anions can be considered the most effective halogen bond (HaB) acceptors among the halides. However, under common experimental conditions, F - uncommonly acts as HaB acceptor, expectedly as it is present in hydrated form. Herein we report that under specific crystallization conditions a hydrogen bond-free F - functioning as donor of electron density can be obtained, with the formed HaBs constituting the driving force of the observed crystal packings. Computations confirm the strength of these HaBs compared to analogous interactions involving other halides.