We will present structural, electrochemical and spectroscopic studies of a family of octanuclear complexes, [Fe8(µ4-O)4(µ-4-R-pz)12X4] -- R = H, Cl, Br, Me, Et; X = Cl, Br, NCS, OPh -- containing a Fe4O4-cubane core, which can be reversibly reduced in four consecutive steps from an all-ferric, [Fe8], to four mixed-valence ferric/ferrous states, [Fe8]-/2-/3-/4-. The close spacing of those redox steps makes those Fe8-complexes quite efficient electron-transfer agents. Spectroscopic analysis of the mixed-valent [Fe8]- species with X = Cl indicates partial charge delocalization over the four Fe4O4-cubane Fe-sites. In contrast, the [Fe8]-/2- species with X = NCS contain FeII-centers fully localized at the outer Fe-sites. Current efforts to fully characterize, structurally, spectroscopically (electronic, vibrational, Moessbauer, XPS) and magnetically the Fe8O4-motif in all its possible oxidation states will be presented. We will also report on recent progress on the synthesis and characterization of analogous [Fe8-xMx(µ4-O)4(µ-4-R-pz)12X4] complexes with M = Ga, In.