The ab initio study of halogen and hydrogen σN-bonded para-substituted pyridine⋯(X2/XY/HX) complexes

Optimal geometries and interaction energies of eleven model para-substituted pyridine⋯X2/XY/HX (X2 = F2, Cl2, Br2; XY = ClF, BrF, BrCl and HX = HF, HCl, HBr) complexes have been investigated systematically at the ab initio MP2 level of theory. Contrary to the hydrogen bonded complexes, the interaction energies of the complexes stabilized via the halogen bond rise with the increase of the atom size in the interacting diatomic molecules. Also, the decrease of the substituentʹs electron withdrawing ability has significant influence on the complex stability. Finally, the evaluated interaction energies correlate reasonably well with the Hammettʹs constants.