Nitronyl Nitroxide-Substituted Benzotriazinyl Tetraradical

High-spin organic tetraradicals with significant intramolecular exchange interactions have high potential for advanced technological applications and basic research, but those synthesized to date possess limited stability and processability. In this work, we designed a tetraradical based on the Blatter’s radical and nitronyl nitroxide radical moieties and successfully synthesized it using the palladium-catalyzed cross-coupling reaction of triiodotriazine with gold(I) nitronyl nitroxide-2-ide complex in the presence of a newly developed efficient catalytic system. The molecular and crystal structure of the tetraradical was confirmed by X-ray diffraction. The tetraradical possesses good thermal stability with decomposition onset at ∼150 °C in an inert atmosphere. The tetraradical exhibits reversible redox waves (at −0.54 and 0.45 V vs Fc/Fc+), unprecedented for high-spin tetraradicals. The magnetic properties of the tetraradical were characterized by SQUID magnetometry of polycrystalline powders and EPR spectroscopy in various matrices. The collected data, analyzed using high-level quantum chemical calculations, confirmed that the tetraradical has a triplet ground state and a nearby excited quintet state. The unique high stability of the prepared triazinyl-nitronylnitroxide tetraradical is a new milestone in the field of creating high-spin systems.