APPROACHES FROM SUPERHIGH-SPIN MOLECULES TO ORGANIC FERROMAGNETS

There arc two steps of strategy in the molecular design of organic ferromagnets: the construction of high-spin organic molecules and the introduction of spin-aligning mechanisms into the assemblies of the open-shell molecules. The former approach requires the knowledge of how to endow organic molecules with many half-filled orthogonal orbitals. In pi-conjugated diradicals, parallel alignment of the two spins can become favored, if the radical centers are placed in phase with the spin polarization of the intervening pi-bonds. We have now studied a wide variety of non-Kekule hydrocarbons and the heteroatom analogues by EPR spectroscopy and magnetic susceptibility/magnetization measurements to find that only a part of them have high-spin ground states. Some of the superhigh-spin molecules from our laboratories will be discussed in some detail. A similar principle can be applied to effect ferromagnetic exchange coupling between high-spin molecules. Design of molecular stacking in crystals, liquid crystals and molecular layers is found to be indispensable.