Magnetism in organic ion radicals; carboxyaryl, sulfoaryl and imidazolyl derivatives of nitronyl nitroxide

In order to study effects of electrostatic attractive forces in polarizable molecules on the magnetism in organic radical crystals, we have synthesized carboxyaryl, sulfoaryl and imidazolyl derivatives of nitronyl nitroxide. Through the analyses of the results of magnetization measurements, coexistence of ferromagnetic and antiferromagnetic intermolecular interactions is revealed in an ion radical salt, sodium 2-sulfonatofuryl nitronyl nitroxide. Coexistence of both magnetic interactions is also observed in carboxymethoxyphenyl, carboxyfuryl, carboxystylyl and carboxyhydroxyphenyl derivatives of nitronyl nitroxide, while 2-imidazolyl nitronyl nitroxide shows quite strong antiferromagnetic intermolecular interaction. These results suggest that carboxy and sulfonato groups give rise to molecular arrangements that favor ferromagnetic intermolecular interaction in organic radical crystals.