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

The tetrel bond formed by HC≡CX, HC=CHX, and HCCHX (X=F, Cl, Br, I) as an electron donor and THF (T=C, Si, Ge) was explored by ab initio calculations. The tetrel bond formed by HCCHX is the strongest, as high as -3.45 kcal/mol for the HCCHF···GeHF dimer, followed by HC=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 HCCHX 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 HC=CHX complexes.