The iron/copper heterodinuclear center in cytochrome c oxidases has attracted the interest of inorganic chemists since this is the site of dioxygen (O-2) four-electron four-proton reduction to water by the reduced enzyme, while the oxidized ("resting") isolated protein dinuclear center exhibits unusual physical, spectroscopic, and ligand-binding properties. We describe here a model compound, [(F-8-TPP)Fe-III-O-Cu-II(TMPA)](+) (3), generated directly from O-2-reduction by 1:1 mixtures of the reduced copper(I) and iron(II) complexes [(TMPA)Cu-I(CH3CN)](+) (1) (TMPA = tris(2-pyridylmethyl)amine) and (F-8-TPP)Fe-II(pip)(2) (2) (F-8-TPP = tetrakis(2,6-difluorophenyl)porpyrinate-(2-), pip = piperidine) in O-2-saturated CH2Cl2 at -80 degrees C;