The electrochemical behaviour of the mu-oxo complexes [(Fe2O)-O-III,III(L)(4)(H2O)(2)](4+) (L = 2,2'-bipyridine (bpy, 1) and (-)4,5-pinene2,2'-bipyridine (pb, 2)) has been investigated in CH,CN. Since some aqua substitution by CH,CN can occur (although, it is not demonstrated clearly) [(Fe2O)-O-III,III(L)(4)(S)(2)](4+) (S = H2O and/or CH3CN is a more accurate notation of complexes 1 and 2 species. Complexes 1 and 2 are reduced irreversibly and on the basis of the electrochemical and spectroscopic data, the reduction process implies an ECC mechanism. The controlled-potential reduction yields an equal amount of the corresponding mononuclear complexes [Fe-II(L)(3)](2+) and an ill-defined 'Fe(III) oxide'. It is suggested that the primary one-electron reduced species [(Fe2O)-O-II,III(L)(4)(S)(2)](3+) (S = H2O or CH3CN) decomposes into the mononuclear complex [Fe-II(L)(2)(S)(2)](2+) by cleavage of the dimeric structure. This mononuclear complex is further transformed into [Fe(L)(3)](2+) by the substitution of the S ligands by one L released from the second iron center, remaining at the +III oxidation state. The transformation of [Fe-II(L)(2)(S)(2)](2+) into Fe(L)(3)](2+) is slower for 2 than for 1 due to larger steric hindrance of the ph ligand versus bpy. Addition of 2 H+ to solutions of 1 and 2 in CH3CN leads to the formation of new dinuclear [(Fe2O)-O-III,III(L)(2)(S)(6)](4+) complexes. Under these conditions the reduction process implies two electrons with quasi-quantitative formation of the mononuclear bis-L complexes [Fe-II(L)(2)(S)(2)](2+) by a controlled-potential reduction. The implication of the redox behaviour of complexes 1 and 2 reported here with regard to their catalytic activity is discussed. It appears that the better stability and efficiency of 2 versus 1 as a catalyst for cyclohexane oxidation with tert-butyl hydroperoxide (TBHP) can be related to the slower rate of conversion of [Fe-II(L)(2)(S)(2)](2+) into the inactive species [Fe(L)(3)](2+) for 2.