Diradical Bis-o-iminosemiquinonato Zinc Complex: Spectroscopy, Magneto- and Electrochemistry

Bis‐o‐iminobenzosemiquinonato zinc and cadmium complexes M(ISQ‐Prⁱ)₂ (M = Zn, 1; M = Cd, 2) were found to be diradical complexes of a distorted tetrahedral geometry according to X‐band EPR spectroscopy. Tetrahedral structure of zinc complex 1 was confirmed by X‐ray diffraction analysis. The spectro‐ and electrochemistry of zinc complex 1 have been studied in details. For 1 a series of reversible one‐electron‐transfer waves leads to the formation of the anions and cations [M(L)₂]^{2−,1−,1+,2+}. All redox processes were shown to be ligand‐based. From variable temperature magnetic susceptibility measurements it has been established that at room temperature 1 possesses an S = 1 state with weak antiferromagnetic coupling between radical ligands (J = −41.4±0.4 cm⁻¹) leading to an S = 0 ground state at low temperature.