Abstract: Novel stable high spin molecules possessing three different arranged fashions are designed with -^·N-N< as a spin-containing(SC) fragment, phenylene as an end group and various aromatic molecules, such as benzene(1), 2,6-pyridine(2), 3,5-pyridine(3), pyridazine(4), 4,6-pyrimidine(5), 2,6-pyrimidine(6), pyrazine(7) and triazine(8), as a ferromagnetic coupling(FC) unit. The effects of the different coupling units 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 results 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. It is shown that the heterocycles as the coupling units have influence on the stabilities of the high-spin ground states. That the heteroatom lying in m-phenyl can improve ferromagnetic coupling, while the heteroatom lying in o-phenyl or p-phenyl is not in favor of the ferromagnetic coupling.

Key words: Heterocycle, Coupling unit, Biradical, High-spin, AM1-CI, B3LYP