Dinuclear non-heme iron clusters containing oxo, hydroxo, or carboxylato bridges are found in a number of enzymes involved in O-2 metabolism such as methane monooxygenase, ribonucleotide reductase, and fatty acid desaturases. Efforts to model structural and/or functional features of the protein-bound clusters have prompted the preparation and study of complexes that contain Fe(mu-O(H))(2)Fe cores. Here we report the structures and spectroscopic properties of a family of diiron complexes with the same tetradentate N4 ligand in one ligand topology, namely [(alpha-BPMCN)(2)Fe(2)(11)mut-OH)(2)](CF3SO3)(2) (1), [(alpha-BPMCN)(2)(FeFe111)-Fe-11((mu)-OH)(2)](CF3SO3)(3) (2), and [(alpha-BPMCN)(2)Fe-2(111)(mu-O)(mu-OH)](CF3SO3)(3) (3) (BPMCN = N, N'-dimethyl-N, N'-bis(2-pyridylmethyl)-trans-1,2-diaminocyclohexane). Stepwise one-electron oxidations of 1 to 2 and then to 3 demonstrate the versatility of the Fe(mu-o(H))(2)Fe diamond core to support a number of oxidation states with little structural rearrangement. Insight into the electronic structure of 1, 2', and 3 has been obtained from a detailed Mossbauer investigation (2' differs from 2 in having a different complement of counterions). Mixed-valence complex 2' is ferromagnetically coupled, with J = -15 +/- 5 cm(-1) (H = JS(1)(.)S(2)). For the S = 9/2 ground multiplet we have determined the zero-field splitting parameter, D9/2 = -1.5 +/- 0.1 cm(-1), and the hyperfine parameters of the ferric and ferrous sites. For T < 12 K, the S = 9/2 multiplet has uncommon relaxation behavior. Thus, MS = -9/2 <----> MS = +9/2 ground state transition is slow while DeltaM(s) = +/-1 transitions between equally signed M-s levels are fast on the time scale of Mossbauer spectroscopy. Below 100 K, complex 2' is trapped in the (Fe1Fe2II)-Fe-III ground state; above this temperature, it exhibits thermally assisted electron hopping into the state (Fe1Fe2III)-Fe-II. The temperature dependence of the isomer shifts was corrected for second-order Doppler shift, obtained from the study of diferrous 1. The resultant true shifts were analyzed in a two-state hopping model. The diferric complex 3 is antiferromagnetically coupled with J = 90 +/- 15 cm(-)1, estimated from a variable-temperature Mossbauer analysis.