The Tetrel Bonds of Hypervalent Halogen Compounds.

The tetrel bond between PhXFY(TF) (T = C and Si; X = Cl, Br, and I; Y = F and Cl) and the electron donor MCN (M = Li and Na) was investigated at the M06-2X/aug-cc-pVDZ level of theory. As the electronegativity of the halogen atom X increases, the strength of the tetrel bond also increases, but as the electronegativity of the halogen atom Y increases, the strength of the tetrel bond decreases. The magnitude of the interaction energy in most -CF complexes was found to be less than 10 kcal/mol, but to exceed 11 kcal/mol for PhClFCl(CF)⋯NCNa. The tetrel bond is greatly enhanced when the -SiF group interacts with LiCN or NaCN, with the largest interaction energy approaching 100 kcal/mol and displaying a covalent Si⋯N interaction. Along with this enhancement, the Si⋯N distance was found to be less than the X-Si bond length, the -SiF group to be closer to the N atom, and in most -SiF systems, the X-Si-F angle to be less than 90°; the -SiF group therefore undergoes inversion and complete transfer in some systems.