MOLECULAR-ORBITAL STUDIES ON THE SPIN STATES OF NITROXIDE SPECIES - BISNITROXYMETAPHENYLENE AND TRISNITROXYMETAPHENYLENE, 1,1-BISNITROXYPHENYLETHYLENE, AND 4,6-DIMETHOXY-1,3-DIALKYLNITROXY BENZENES

We describe by approximate Mo calculation a number of species for whic h high spin states are either the ground state or lie very low in ener gy. These are models for the spin coupling in projected ferromagnetic organic materials. The theory guiding their construction is based on p lanar conjugated systems, while experimentally realized systems are of ten far from planarity. We can by appeal to steric decoupling explain the failure of the prediction that methoxy subsitution on metaphenylen e-coupled nitroxides should stabilize the triplet. However, we find in general that the qualitative rules derived from discussion of planar systems are robust; drastic departures from planarity are required bef ore they lose their value. (C) 1996 John Wiley & Sons, Inc.