| Summary: | The tetrel bond between PhXF<sub>2</sub>Y(TF<sub>3</sub>) (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<sub>3</sub> complexes was found to be less than 10 kcal/mol, but to exceed 11 kcal/mol for PhClF<sub>2</sub>Cl(CF<sub>3</sub>)⋯NCNa. The tetrel bond is greatly enhanced when the –SiF<sub>3</sub> 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<sub>3</sub> group to be closer to the N atom, and in most –SiF<sub>3</sub> systems, the X–Si–F angle to be less than 90°; the –SiF<sub>3</sub> group therefore undergoes inversion and complete transfer in some systems.
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