C–H···BF2O2Interactions in Crystals: A Case for Boron Hydrogen Bonding?

Molecules bearing the borondifluoride unit represent an important class of dyes. We report the intriguing occurrence of short H···B contacts in the crystal structure of compounds featuring the BF 2 O 2 fragment. Using density functional theory-based calculations, we discovered that, in contrast to what is suggested by the structural observation, the driving force behind these short H···B contacts is not a direct H···B interaction but it relies on the existence of a combination of single, bifurcated, or trifurcated hydrogen bond paths that are practically isoenergetic within a broad range of C–H···B interaction orientations. The BF 2 O 2 group as a whole displays a very isotropic hydrogen bonding ability and, in turn, a strong adaptability to structural requirements in the solid state.