Effect of carbon hybridization in C-F bond as an electron donor in triel bonds

The ability of the F atom of HC equivalent to CF, H2C=CHF and H3CCH2F to serve as an electron donor to the triel (Tr) atom of TrR3 in the context of a triel bond is assessed by ab initio calculations. The triel bond formed by C-sp3-F is strongest, as high as 30 kcal/mol, followed by C-sp2-F, and then by C-sp-F whose triel bonds can be as small as 1 kcal/mol. The noncovalent bond strength diminishes in the order Tr = Al > Ga > B, consistent with the intensity of the pi-hole above the Tr atom in the monomer. The triel bond strength of the Al and Ga complexes increases along with the electronegativity of the R substituent but is largest for R=H when Tr=B. Electrostatics play the largest role in the stronger triel bonds, but dispersion makes an outsized contribution for the weakest such bonds.