Effects of Lewis Basicity and Acidity on σ-Hole Interactions in Carbon-Bearing Complexes: A Comparative Ab Initio Study

The effects of Lewis basicity and acidity on σ-hole interactions were investigated using two sets of carbon-containing complexes. In Set I, the effect of Lewis basicity was studied by substituting the X(3)/X atom(s) of the NC-C(6)H(2)-X(3) and NCX Lewis bases (LB) with F, Cl, Br, or I. In Set II, the W-C-F(3) and F-C-X(3) (where X and W = F, Cl, Br, and I) molecules were utilized as Lewis acid (LA) centers. Concerning the Lewis basicity effect, higher negative interaction energies (E(int)) were observed for the F-C-F(3)∙∙∙NC-C(6)H(2)-X(3) complexes compared with the F-C-F(3)∙∙∙NCX analogs. Moreover, significant E(int) was recorded for Set I complexes, along with decreasing the electron-withdrawing power of the X(3)/X atom(s). Among Set I complexes, the highest negative E(int) was ascribed to the F-C-F(3)∙∙∙NC-C(6)H(2)-I(3) complex with a value of −1.23 kcal/mol. For Set II complexes, E(int) values of F-C-X(3) bearing complexes were noted within the −1.05 to −2.08 kcal/mol scope, while they ranged from −0.82 to −1.20 kcal/mol for the W-C-F(3) analogs. However, V(s,max) quantities exhibited higher values in the case of W-C-F(3) molecules compared with F-C-X(3); preferable negative E(int) were ascribed to the F-C-X(3) bearing complexes. These findings were delineated as a consequence of the promoted contributions of the X(3) substituents. Dispersion forces (E(disp)) were identified as the dominant forces for these interactions. The obtained results provide a foundation for fields such as crystal engineering and supramolecular chemistry studies that focus on understanding the characteristics of carbon-bearing complexes.