Comparison for Electron Donor Capability of Carbon-Bound Halogens in Tetrel Bonds.

The tetrel bond formed by HC≡CX, H2C=CHX, and H3CCH2X (X=F, Cl, Br, I) as an electron donor and TH3F (T=C, Si, Ge) was explored by ab initio calculations. The tetrel bond formed by H3CCH2X is the strongest, as high as -3.45 kcal/mol for the H3CCH2F···GeH3F dimer, followed by H2C=CHX, and the weakest bond is from HC≡CX, where the tetrel bond can be as small as -0.8 kcal/mol. The strength of the tetrel bond increases in the order of C < Si < Ge. For the H3CCH2X and HC≡CX complexes, the tetrel bond strength shows a similar increasing tendency with the decrease of the electronegativity of the halogen atom. Electrostatic interaction plays the largest role in the stronger tetrel bonds, while dispersion interaction makes an important contribution to the H2C=CHX complexes.