The CF⋅⋅⋅HCF2 interaction: A combination of hydrogen bonding and n → σ* stabilization

In this communication, we explore a unique molecule that exhibits a substantial interaction between a CF₂H group and a CF group.  In medicinal chemistry, CF₂H groups are known as weak hydrogen bond donors, and CF groups as weak H-bond acceptors.  Seldom are they paired up together in an array such that their unique properties can be examined.  In this case, we establish that along with an attractive hydrogen bonding interaction, an n → σ* component anchors the interactions. A unique combination of steric and hyperconjugative effects ‘switches’ the interaction away from previously reported dominant tetrel-type bonding in the case of a CH₂F and CF interation towards an unusualy complex hybrid interaction.  Crystallographic, computational, and spectroscopic studies illuminate the problem.