C-H•••BF2O2 Interactions 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 center dot center dot center dot B contacts in the crystal structure of compounds featuring the BF2O2 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 center dot center dot center dot B contacts is not a direct H center dot center dot center dot 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 center dot center dot center dot B interaction orientations. The BF2O2 group as a whole displays a very isotropic hydrogen bonding ability and, in turn, a strong adaptability to structural requirements in the solid state.