Possible superhigh-spin cluster in the crystals of a novel nitronyl nitroxide radical as studied by FT pulsed ESR

Syntheses and magnetic properties of novel nitronyl nitroxide derivatives a re reported. In the derivatives under study, the bulky tetramethylethylene group of the conventional nitronyl nitroxide has been replaced by aromatic rings, giving planar pi-conjugation systems. The first half of the paper is devoted to the syntheses and characterization of new derivatives of such r adical, 2-phenylbenzimidazol-1-yl-N,N'-dioxide (PBIDO). Chemical stability, pi-spin density distribution, and solid state magnetic properties have bee n examined from solution ESR and static susceptibility measurements. In the latter half, we discuss an anomaly of paramagnetic relaxation found in cry stals of PBIDO by pulsed ESR spectroscopy The origin of the anomaly is attr ibuted to a possible formation of paramagnetic species with huge S, or "sup erhigh-spin cluster" at lattice defects in the crystal.