Theoretical Design of High-spin Organic Molecules with ˙ NS as a Spin-containing Fragment and Heterocycle as End Groups1

Novel stable high-spin molecules possessing three different arranging fashions were designed with ˙NS as a spin-containing (SC) fragment, an aromatic group, such as benzene (1), pyridine (2), pyridazine (3), pyrimidine (4), pyrazine (5) or triazine (6) as end groups (EG), and phenyl as a ferromagnetic coupling (FC) unit. The effects of different EG on the spin multiplicities of the ground states and their stabilities were investigated by means of the AM1-CI approach. All the investigated molecules corresponded to the FC and possessed high-spin ground states. The spin on the two atoms of the SC fragment was not in agreement with the delocalization results in the specific stability of ˙NS. In those molecules, the stabilities of the triplet states decreased when the distance between the atoms of central SC fragments (N) increased. The stabilities of the triplet states of compounds 1a-n, 1b-n and 1c-n, with heterocycles as EG were higher than those of the triplet states of those compounds with phenyl as EG. Furthermore, the stabilities of the triplet states of the compounds with pyrimidine and triazine as EG were higher than those with pyridine, pyridazine or pyrazine as EG.