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···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···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 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.含二氟化硼结构单元的分子属于一类重要的染料化合物。我们报道了含BF2O2片段的化合物晶体结构中存在的短程H···B接触这一引人关注的现象。通过基于密度泛函理论（density functional theory）的计算研究，我们发现：与晶体结构观测结果的直观推论相悖，这类短程H···B接触的驱动力并非直接的H···B相互作用，而是依托单重、双分叉或三分叉氢键路径的组合；在宽泛的C–H···B相互作用取向范围内，这些氢键路径的能量几乎完全等价。BF2O2基团整体展现出极强的各向同性氢键结合能力，进而在固态环境中对结构需求具备出色的适配性。