The unsymmetrical N,O-dibridging NO₂^– group in the threo (‘rac’) or erythro (‘meso’) isomers of [(en)₂Co(μ-NH₂,μ-NO₂)Co(en)₂]⁴⁺ is cleaved in hot triflic acid to yield a complex that is predominantly meso. This reacts in water to yield the new meso-[(en)₂Co(μ-NH₂,μ-OH)Co(en)₂]⁴⁺ ion. The reactions of the threo- and erythro-μ-NO₂^– isomers in basic (0.1 M) aqueous solution are each retentive, giving the rac- and meso-[(en)₂Co(μ-NH₂,μ-OH)Co(en)₂]⁴⁺ ions as products, respectively. The optically resolved erythro complex gives the achiral meso isomer, which completes the threo/rac and erythro/meso chemical correlations between the two series of dinuclear complexes; the meso synthesis completes the pair – the meso- and rac-[(en)₂Co(μ-NH₂,μ-OH)Co(en)₂]⁴⁺ ions. In HCl, stable μ-Cl, μ-NH₂ dinuclear ions are formed from these μ-NH₂, μ-OH complexes, with retention. The peroxo or superoxo ions rac-[Co(en)₂(μ-NH₂,μ-O₂)Co(en)₂]ⁿ⁺ react with Sn^II to produce symmetrically bridged intermediates that decay to the common and new meso-[(en)₂Co(μ-NH₂,μ-OH)Co(en)₂]⁴⁺ isomer on reaction in Me₂SO. Both the rac and meso isomers of the μ-hydroxo-μ-peroxo complexes are also reduced by Sn^II to give intermediates that in Me₂SO decay to the respective diols with retention. The new rac-[Co(en)₂(μ-OH)₂Co(en)₂]⁴⁺ and meso-[(en)₂Co(μ-NH₂,μ-OH)Co(en)₂]⁴⁺ isomers complete the characterization of rac/meso pairs in both systems. The corresponding μ-sulfate pairs are also reported.