A DFT and AIM study of the interactions of pyridine and pyrazine with alkali hydrides. Identification of dihydrogen bonds involving aromatic C-H hydrogen

Abstract

The interactions of pyridine (py) and pyrazine (pz) with LiH, NaH and KH are studied by DFT at the B3LYP/6-311++g(2d,p) level. The interaction energies corrected for BSSE lie in the range −86.7 to −38.8 kJ mol^-1. Dihydrogen bonds are observed only for the py-KH and pz-KH systems with distances 2.27 and 2.17 Å respectively. AIM analyses show presence of bond critical points, associated with an electron density of 0.011-0.013. Our calculations on the ammonia borane dimer, where presence of dihydrogen bond is authentic, at the same level of theory reveal that the electron density at the bond critical points of the dihydrogen bonds (of calculated lengths 2.03-2.05 Å) is 0.015.