The crystal structures of two dinuclear iron(III) complexes containing an oxo bridge, [Fe2OCl2L2][ClO4]2·2H2O 1[L =N,N-bis(2-pyridylmethyl)glycinamide] and [Fe2OCl2L2][ClO4]22(L =N-{2-[bis(2-pyridylmethyl)amino]ethyl}morpholine) were determined. Their structural features are quite similar to those of the corresponding linear dinuclear complex [Fe2OCl2(tpa)2][ClO4]2, where tpa is tris(2-pyridylmethyl)amine; the ligands act as tetradentate tripods, and the Fe–O (amide) and average Fe–N (morpholine) distances are 2.165(6) and 2.45(1)Å, respectively. Complex 1 exhibited much higher activity for the hydroxylation of cyclohexane in the presence of H2O2, while the activities of the other two complexes are negligible. In contrast, all three complexes exhibited high activity for the decomposition of H2O2. These results indicate that the active species for oxygenation of cyclohexane, which may be an iron(III)–peroxide adduct (I), should be different from that for decomposition of H2O2, adduct II, and that these two species may exist in the solution of complex 1. It is postulated that adduct I may be a dinuclear iron(III)–η1-hydroperoxide species stabilized through hydrogen bonding between the hydroperoxide ion and the oxygen atom of the amide group. Extended-Hückel molecular orbital calculations showed that the hydrogen bonding may lead to induction of high ‘oxo-like’ activity in the peroxide adduct. In the cases of the tpa and morpholine complexes the formation of a η1-hydroperoxide adduct seems unfavourable because of both steric and electronic reasons; instead a (µ-η1:η1-peroxo)diiron(III) species, adduct II, is formed which induces high catalase-like activity.