Structure, spectroscopy and magnetic properties of Zn, Mn and Co complexes of a pyridine bis(imine) bis(nitroxide) ligand

A pyridine–diimine (N3) pincer ligand, denoted L , was functionalized with two TEMPO moieties. The Zn 2+ , Mn 2+ and Co 2+ complexes were isolated and structurally characterized, showing a pentacoordinated metal center, with two exogenous chloride ligands. All exhibit the typical 3-line pattern of nitroxide radicals in their EPR spectrum. The magnetic interaction between the metal and the nitroxide moieties is negligible, as demonstrated by SQUID magnetometry. Both the ligand and complexes exhibit a reversible oxidation wave at 0.30–0.35 V vs. Fc + /Fc, which corresponds to the simultaneous oxidation of both TEMPO groups into oxoammonium species. This is verified by a quenching of the nitroxide lines in the EPR spectrum during controlled potential electrolysis, as well as the appearance of shoulders around 450–500 nm in UV–Vis spectroscopy. DFT calculations support a ligand-centered oxidation, and the high spin configuration of the complexes. • The TEMPO units undergo reversible oxidation, enabling their use as efficient redox-responsive sensors. • Intramolecular magnetic interactions (metal–radical and radical–radical) are negligible, ensuring predictable magnetic behaviour. • The metal ions remain high-spin and redox-inert within the explored potential window, providing complexes with maximized total spin (S), a key advantage for imaging applications.