Binuclear complexes of cobalt(III) have been prepared with 3,3',4,4'-tetrahydroxy-benzaldazine (H(4)thB), 3,3',4,4'tetrahydroxy-5,5'-dimethoxybenzaidazine (H(4)thM), and 3,3',4,4'-tetrahydroxydimethylbenzaldazine (H(4)thA) as bis(catecholate) ligands that link metal ions separated by 16 A through a conjugated bridge. In one case, [CO2(bpy) (4)(thM)](2+), stereodynamic properties observed in solution by H-1 NMR are associated with valence tautomerism, with formation of a labile hs-Co(II) species by electron transfer from the catecholate regions of the bridge. Electrochemical oxidation of the complexes occurs at the bridges as two closely spaced one-electron couples. Chemical oxidation Of [CO2(bPY) (4)(thB)](2+) with Ag+ is observed to occur as a two-electron process forming [CO2(bPY) (4)(thB(SQ,SQ))](4+). Attempted crystallization in the presence of air was observed to result in formation of the [Co(bpy)(2)(BACat)](+) (H(2)BACat, 3,4-dihydroxybenzaldehyde) cation by aerobic oxidation. Structural characterization is provided for the HAM ligand and [Co(bPY)2(BACat)](BF4).