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High-spin organic tetraradicals with significant intramolecular exchange interactions have high potential for advanced technological applications and fundamental research, but examples reported to date exhibit limited stability and processability. In this work, we designed the first tetraradical based on an oxoverdazyl core and nitronyl nitroxide radicals and successfully synthesized it using a palladium-catalyzed cross-coupling reaction of an oxoverdazyl radical bearing three iodo-phenylene moieties with a gold(I) nitronyl nitroxide-2-ide complex in the presence of a recently developed efficient catalytic system. The molecular and crystal structures of the tetraradical were confirmed by single crystal X-ray diffraction analysis. The tetraradical possesses good thermal stability with decomposition onset at ∼125 °C in an inert atmosphere; in a toluene solution upon prolonged heating at 90 °C in air, no decomposition was observed. The resulting unique verdazyl-nitroxide conjugate was thoroughly studied using a range of experimental and theoretical techniques, such as SQUID magnetometry of polycrystalline powders, EPR spectroscopy in various matrices, cyclic voltammetry, and high-level quantum chemical calculations. All collected data confirm the high thermal stability of the resulting tetraradical and quintet multiplicity of its ground state, which makes the synthesis of this important paramagnet a new milestone in the field of creating high-spin systems.

Gold(I) derivatives of nitronyl nitroxide (NN) stabilized by complexation with phosphine ligands were designed to promote dimerization of the paramagnets in the solid state via Au–Au bonding. The complexes were successfully synthesized by the reaction of the corresponding phosphine [n-Bu3P or (4-FC6H4)3P], AuCl(THT), and NN–H under basic conditions in high yields. The gold(I) complexes were characterized by cyclic voltammetry, electron spin resonance, infrared, and UV/vis spectroscopy supported by quantum chemical calculations. Crystallographic analyses of the complexes showed that they possess Au–Au bonds (2.930 and 3.095 Å). The Au–Au bonding was confirmed by density functional theory calculations and quantum theory of “atoms in molecules” and natural bond orbital analyses, which made it possible to determine bond critical points (3, −1) and Au–Au bond orders (0.36 and 0.23) as well as to estimate the orbital contribution to the energy of Au–Au bonds (12.0 and 8.6 kcal/mol).