“Criss-Crossed” Dinucleating Behavior of an N4 Schiff Base Ligand: Formation of a μ‑OH,μ‑O2 Dicobalt(III) Core via O2 Activation

We report the synthesis and structural characterization of a dicobalt­(III) complex with a μ-OH,μ-O2 core, namely μ-OH,μ-O2-[Co­(enN4)]2(X)3 [1­(ClO4)3 and 1­(BF4)3]. The dinuclear core is cross-linked by two N4 Schiff base ligands that span each cobalt center. The formally CoIII–CoIII dimer is formed spontaneously upon exposure of the mononuclear Co­(II) complex to air and exhibits a ν­(O–O) value at 882 cm–1 that shifts to 833 cm–1 upon substitution with 18O2. The CV of 1­(BF4)3 exhibits a reversible {CoIII–CoIII}↔{CoIII–CoIV} redox process, and we have investigated the oxidized {CoIII–CoIV} species by EPR spectroscopy (g = 2.02, 2.06; S = 1/2 signal) and DFT calculations.