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 are reported. In the derivatives under study, the bulky tetramethylethylene group of the conventional nitronyl nitroxide has been replaced by aromatic rings, giving planar π-conjugation systems. The first half of the paper is devoted to the syntheses and characterization of new derivatives of such radical, 2-phenylbenzimidazol-l-yl-N,N′-dioxide (PBIDO). Chemical stability, π-spin density distribution, and solid state magnetic properties have been examined from solution ESR and static susceptibility measurements. In the latter half, we discuss an anomaly of paramagnetic relaxation found in crystals of PBIDO by pulsed ESR spectroscopy. The origin of the anomaly is attributed to a possible formation of paramagnetic species with huge S, or "super-high-spin cluster" at lattice defects in the crystal.