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

[Image: see text] The tetrel bond formed by HC≡CX, H(2)C=CHX, and H(3)CCH(2)X (X=F, Cl, Br, I) as an electron donor and TH(3)F (T=C, Si, Ge) was explored by ab initio calculations. The tetrel bond formed by H(3)CCH(2)X is the strongest, as high as −3.45 kcal/mol for the H(3)CCH(2)F···GeH(3)F dimer, followed by H(2)C=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 H(3)CCH(2)X 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 H(2)C=CHX complexes.