Calculations of zero-field splittings in pyridine derivatives

Abstract

Zero-field splittings were calculated for benzene, pyridine, and a number of simple derivatives. The experimental decrease of the zfs parameter D upon addition of substituents on the benzene and pyridine rings and upon protonation of pyridine was reproduced theoretically without invoking either aplanarity or nπ* interaction. For a lowest ππ* triplet state of pyridine, D = 0.165 cm−1 and E = −0.020 cm−1 are predicted. Zfs integrals were calculated from a wave function formed from CNDO/2 orbitals with two-configuration CI, using a five-term Gaussian expansion with the best Slater exponents for atoms in molecules.