ON THE COMPLEXITIES OF SHORT-RANGE FERROMAGNETIC EXCHANGE IN A NITRONYL NITROXIDE

The molecular solid state structure and properties of 2-(4-nitrophenyl)-4,4,5,5-tetramethy-4,5-dihydro-1H-imidazolyl-1-oxyl 3-oxide (1) were examined. The solid state structure of two (alpha and beta) out of three phases, together with relevant short intermolecular contacts (to 3.60 angstrom) are presented. Solid state phase transformations, as detected by differential scanning calorimetry and electron spin resonance are described. As reported previously by Awaga, one phase of 1 exhibits short range intermolecular ferromagnetic interaction of the unpaired electrons. Explanation for the structural origin of this electron-electron interaction is hampered by the fact that 1 forms structurally completely different solid state phases, yet each phases shows qualitatively the same temperature dependance of the magnetic susceptibility but different electron spin resonance linewidths and linewidth behavior as a function of temperature.