A simple rule to find nondisjoint NBMO degenerate systems for designing high-spin organic molecules

For predicting organic ferromagnetic substances, we propose a simple rule to estimate the possibility as a high-spin molecule, based on molecular orbital coefficients by the simple Hückel's nonbonding molecular orbital (NBMO) method for organic conjugated systems. For the combination of several molecules in which each molecule has an NBMO, it was found that the NBMO levels (ε = α) of original isolated molecules are conserved by the linkage between a starred atom in one molecule and an unstarred atom in the other molecule and, moreover, this type of NBMO degenerate system can be preferable to the high-spin state. By combining several molecules in such a manner, N degenerate systems are generated according to the number of molecules included, N. In the supermolecule thus obtained, an index which represents the degree of possessing a ferromagnetic property is defined and its reliability is examined by ab initio calculations for several model, molecules.