The electronic structures of four members of the electron-transfer series [Fe-2(L-1)(4)](n) (n = 2-, 1-, 0, 1+) have been elucidated in some detail by electronic absorption, IR, X-band electron paramagnetic resonance (EPR), and Mossbauer spectroscopies where (L-1) 2- represents the ligand 1,2- bis(4-tert-butylphenyl)-1,2-ethylenedithiolate(2-) and (L-1 center dot)is its d-radical monoanion. It is conclusively shown that all redox processes are ligand-centered and that highvalent iron(IV) is not accessible. The following complexes have been ynthesized: [Fe-2(III)(L-1 center dot)(2)(L-1)(2)](0) (1), [Fe-2(III)(L-2 center dot)(2)(L-2)(2)]center dot 2CH(2)Cl(2) (1') where (2L) 2- is 1,2- bis(p-tolyl)-1,2-ethylenedithiolate(2-) and (L-2 center dot)-represents its d-radical monoanion, [Cp2Co][Fe-2(III)(L-1 center dot)(L-1)(3)], 4(toluene)center dot 0.5Et(2)O (2), and [Cp2Co](2)[Fe-2(III)(L-1)(4)], 2(toluene) (3). The crystal structures of 1' and 2 have been determined by single-crystal X-ray crystallography at 100 K. The ground states of complexes have been determined by temperature-dependent magnetic susceptibility measurements and EPR spectroscopy: 1' and 1 are diamagnetic (S-t = 0); 2 (S-t = 1/ 2); 3 (S-t = 0); the monocation [Fe-2(III)(L-1 center dot)(3)(L-1)](+) possesses an St = 1/2 ground state (S-t = total spin ground state of dinuclear species). All species contain pairs of intermediate-spin ferric ions (S-Fe = 3/2), which are strongly antiferromagnetically coupled (H = -2JS(1)center dot S-2, where S-1 = S-2 = 3/2 and J = similar to-250 cm(-1)).