"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 Co(III)-Co(III) 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 (18)O2. The CV of 1(BF4)3 exhibits a reversible {Co(III)-Co(III)}↔{Co(III)-Co(IV)} redox process, and we have investigated the oxidized {Co(III)-Co(IV)} species by EPR spectroscopy (g = 2.02, 2.06; S = 1/2 signal) and DFT calculations.