Theoretical Design of High-spin Organic Molecules with —·N—N— as a Spin-containing Fragment and Heterocycles as an End Group

Novel stable high spin molecules possessing three different arranged fashions are designed with –·N–N< as a spin-containing (SC) fragment, various aromatic, such as benzene (1), pyridine (2), pyridazine (3), pyrimidine (4), pyrazine (5), triazine (6) as end groups (EG) and phenyl as a ferromagnetic coupling (FC) unit. The effects of a different end groups on the spin multiplicities of the ground states and their stabilities were investigated by means of AM1-CI approach. It has been found that the spin densities on the two atoms of the SC fragment are different from delocalization resulting in the specific stability of –·N–N<. In these molecules, the stabilities of the triplet states decrease when the distance between the atoms of central SC (–N–) increases. The orders of the stability of triplet states for 1an, 1bn, 1cn [They are isomers in which SC is connected with FC in different way (1an, N₁NNN₁; 1bn, N₁N N₁N; 1cn, NN₁N₁N) and six heterocycles are EG] show that the stability of triplet states with heterocycles as end groups is higher than that with phenyl as end groups, and in the order:triazine (EG)>pyrimidine, pyrazine>pyridine, pyridazine.