Influence of halogen atom substitution and neutral HCN/anion CN Lewis base on the triel-bonding interactions.

Triel-bonding interactions composed of Lewis acid TrOHH/TrOHX/TrOHX (Tr = B, Al, Ga; X = F, Cl, Br) molecule and Lewis base neutral HCN or anionic CN molecule are of research significance in bond properties, which has been investigated at MP2/aug-cc-pVTZ theory level. It is also feasible to study the halogen atom substituent effect and influence of different Lewis bases on the formation of triel bond. AIM analyses reveal that Tr (Tr = B, Al, Ga)···N bond critical point (BCP) exists in all studied triel bond. In the formation of triel bonding, compared with Lewis base HCN molecule, Lewis base anionic CN can participate in a stronger triel bond. Specifically, the structural change, deformation energy, and charge transfer of CN complexes are all larger than that of HCN complexes. In addition, halogen atom substitution effect is also discussed. MEP value and binding energy of HCN and CN complexes all increase after replacing one or two hydrogen atoms by halogen atoms (F, Cl, Br) in Lewis acid. Especially, replacing two hydrogen atoms by halogen atoms in Lewis acid has more remarkable enhancement in MEP value and binding energy than that of replacing only one hydrogen atom. After replacement, binding energy can be increased by 21.77 kcal/mol. The neutral and anionic triel-bonded complexes composed by Lewis acid TrOHH/TrOHX/TrOHX (Tr = B, Al, Ga; X = F, Cl, Br) with Lewis base HCN and CN are systematically investigated at MP2/aug-cc-pVTZ level. The neutral (HCN) triel bonding is weaker than the anionic (CN) triel bonding due to the smaller MEP value of the neutral HCN molecule. The replacement of hydrogens (-H) in Lewis acid by electron-withdrawing groups (-F, -Cl, -Br) has a prominent enhancement effect on the MEP value of π-hole and triel-bonding strength.