Cooperative effects between triel and halogen bonds in complexes of pyridine derivatives: An opposite effect of the nitrogen oxidation on triel and halogen bonds

Abstract

AbstractAb initio calculations are performed for binary complexes of TrR3···4‐PyX/4‐OPyX and 4‐PyX/4‐OPyX···N‐base (Tr = B, Al; R = H, Cl, Br, I; X = Cl, Br, I; N‐base = HCN, NHCH2, NH3). The halogen bond (XB) is weak but becomes stronger in the HCN(sp) < NH3(sp3) < NHCH2(sp2) pattern. Nitrogen oxidation can enhance the XB a little. The triel bond (TrB) is very strong, with interaction energy ranging from −35 to −58 kcal/mol. The TrB is weaker for the heavier halogen atom in the AlR3 complex, while no such dependence is found in the BR3 complex. The oxygen atom of 4‐OPyX engages in a weaker TrB than the nitrogen atom of 4‐PyX, inconsistent with the negative molecular electrostatic potentials (MEPs) on both atoms. Both TrB and XB are strengthened in TrR3···4‐PyX/4‐PyOX···N‐base. The binding distance of the stronger TrB is shortened to less than that of the weaker XB, which is in contrast to that in BF3···NCH···NCH, where the stronger TrB has a larger shortening in the binding distance. The cooperativity is explained by MEP and charge transfer.