Comparison of triel bonds with different chalcogen electron donors: Its dependence on triel donor and methyl substitution

The complexes between R₃Tr (Tr = B, Al, and Ga; R = H, F, Cl, and Br) and H₂X (X = O, S, and Se) were theoretically studied. The interaction energies of R₃Al⋯H₂X and R₃Ga⋯H₂X are consistent with the electronegativity of the halogen atom R (R ≠ H), but an opposite dependence is found for R₃B⋯H₂X. The triel bond of R₃Tr⋯H₂X is weaker for the heavier chalcogen donor. The dependence of triel bonding strength on the triel atom is complicated, depending on the nature of R and X. The methyl substitution of H₂X causes a substantial increase in the interaction energy from −5.74 kcal/mol to −22.88 kcal/mol, and its effect is relevant to the nature of Tr, X, and R groups. For the S and Se donors, the increased percentage of interaction energy is almost the same due to the methyl substitution, which is larger than that of the O analogue. In most triel-bonded complexes, electrostatic dominates and polarization has comparable contribution. However, polarization plays a dominant role in R₃B⋯ and R₃B⋯ (R = Cl and Br; R′ = H and Me).