Theoretical design of high-spin biradical molecules with heterocycles as coupling unit

Computational studies of a class of potentially stable high-spin biradicals that two-atom-three-electron spin centers SC units connected by heterocycles FC and phenyl EG were described. The geometry and character of the spin exchange interaction were obtained by means of UB3LYP/6-31G*. The results show that the molecules possessing three different arranged fashions are designed with ·NS as SC fragment, pyridine as FC and phenyl as EG, the spin densities on the two atoms of the SC fragment are different from the delocalization results in the specific stability of ·NS. In these molecules, the stabilities of the triplet states decrease when the distance between the atoms of central SC (N) increases. Molecules with ·NS as SC fragment, pyridine, pyrazine and triazine as FC and phenyl as EG are designed, the stability of triplet states for the molecule with pyridine as FC is the highest, and that for the molecule with pyrazine as FC is the lowest. Molecules with ·NS, ·NO and ·NNH as SC fragment, pyridine as FC and phenyl as EG are designed, the stability of triplet states for the molecule with ·NS as SC is the highest, that for the molecule with ·NNH as SC is the lowest.