Strong lone pair⋯π interactions between amine and tri-s-triazine derivatives: A theoretical investigation

For a better understanding of the interesting lone pair⋯π (lp⋯π) interaction, MP2 and CCSD(T) calculations have been carried out to investigate the nitrogen lp⋯π interactions between amine and tri-s-triazine derivatives. New strong attractive lp⋯π interactions are observed when the lone pairs of NH3 and NMe3 point toward the large π system, tri-s-triazine ring. At the CCSD(T)/6-311++G(d,p)//MP2/6-311G(d,p) level, the BSSE corrected interaction energy of the C6N7H3⋯NH3 complex is −6.3 kcal mol−1,which is larger than those of the most previously reported lp⋯π systems. The substitution effects on interaction energy of the present studied systems were studied to probe how to manipulate lp⋯π interaction and obtain stronger one. The results indicate that the very strong lp⋯π interaction can form between electron-rich amines and electron-deficient large aromatic ring. But the lp⋯π interactions between the electron-deficient amine such as NF3 and aromatic ring are very weak. The C6N7F3⋯NMe3 complex has interaction energy of −9.8 kcal mol−1. This interaction is much stronger than previously reported lp⋯π bindings. The AIM analysis of the nine studied complexes shows that their molecular graphs are obvious different from previously reported benzene⋯amine complexes and X–H/π systems, which may result from the tri-s-triazine ring’s characteristic.