Hydrogen-Bonded Dimeric Synthon of Fluoro-Substituted Phenylboronic Acids versus Supramolecular Organization in Crystals

An analysis of crystal structures of a series of fluoro-substituted phenylboronic acids is presented. Interplay between the structure of a basic H-bonded dimeric R²₂(8) synthon and a higher-order supramolecular organization is highlighted. The elucidation of hydrogen bonds formed by the boronic B­(OH)₂ moiety is supported by energy calculations based on a one-dimensional H-bond model as well as by Hirshfeld surface analysis. The results revealed that intramolecular O–H···F hydrogen bonds are insignificant compared to O–H···O ones in dimers in controlling the syn–anti conformation of the boronic group. Depending on the strength of H-bonds in the basic motif, forces constituting so-called large synthons change from O–H···O hydrogen bonds to stacking interactions. This differentiation entails the twist of the boronic group with respect to the phenyl ring. The large synthons serve as main building blocks for three-dimensional structures either by their close packing or by the aid of weak secondary interaction such as C–H···π, O–H···F, or C–H···F hydrogen bonds. The observed isomorphism and polymorphism are discussed in relation to the packing of one-dimensional large synthons.