H3O2–, O22– and O2˙– bridging ligands in cobalt(iii) complexes of an acyclic phenolate-hinged dinucleating ligandElectronic supplementary information (ESI) available: Fig. S1: Raman spectra of [Co2(bpbp)(µ-O2)(µ-CH3CO2)]2+ (top) and the superoxo-bridged complex [Co2(bpbp)(µ-O2)(µ-CH3CO2)]3+ (bottom). Fig. S2: ESI-MS spectra of the peroxo bridged [Co2(bpbp)(µ-O2)(µ-CH3CO2)]2+. Fig. S3: ESI-MS spectrum of the superoxo bridged [Co2(bpbp)(µ-O2)(µ-CH3CO2)]3+. See http://www.rsc.org/suppdata/dt/b2/b210091f/

The dicobalt(III) complex, [Co2(bpbp)(μ-H3O2)2](ClO4)3 (bpbp− = 2,6-bis[bis(2-pyridylmethyl)aminomethyl]-4-tert-butylphenolate), obtained by reaction of cobalt(II) perchlorate with Hbpbp under ambient conditions contains two μ-H3O2− bridging ligands. The H-bonded O⋯O distances in this motif are 2.437(3) and 2.456(4) Å, respectively, with a Co⋯Co separation of 3.601(1) Å. The structurally precedented peroxo bridged complexes, [Co2(bpbp)(μ-O2)(μ-RCO2)](ClO4)2 (R = CH3 or C6H5), are formed if a carboxylate is present. The X-ray crystal structure showed O–O and Co⋯Co distances of 1.422(3) and 3.168(1) Å, respectively, in the case of R = CH3. ESI-MS shows that the bridging peroxo ligand is easily eliminated from [Co2(bpbp)(μ-O2)(μ-CH3CO2)]2+, m/z 390.0, as implicated by the observation of [Co2(bpbp)(μ-CH3CO2)]2+, m/z 374.1, corresponding to loss of the mass equivalent of dioxygen. The superoxo complex [Co2(bpbp)(μ-O2)(μ-CH3CO2)]3+ can be prepared by Ce(IV) oxidation of [Co2(bpbp)(μ-O2)(μ-CH3CO2)]2+. Reaction of [Co2(bpbp)(μ-H3O2)2]3+ with hydrazine in air gives the dicobalt(II) complex [Co2(bpbp)(NH2NHCO2)2]ClO4. In this complex the two exogenous hydrazinecarboxylato ligands are bound to individual metal ions with weak H-bonding between them as shown by X-ray structure analysis.