Three iron complexes of the meso-dioxo derivative of octaethylporphryin (trans-H(2)OEPO(2)) were characterized by X-ray diffraction. Green ClFeIII(trans-OEPO(2)). 1.5C(6)H(6) crystallizes in the monoclinic space group P2(1)/c with a = 13.766(3) Angstrom, b = 19.075(3) Angstrom, c = 15.217(3) Angstrom, beta = 99.87(2)degrees at 123 K with Z = 4. Refinement of 2712 reflections with F > 6.0 sigma(F) and 223 parameters yielded R = 0.0624, R(w) = 0.0596. The iron complex contains a domed dioxoporphodimethene macrocyclic ligand. The observation of a five-coordinate iron(III) ion with an axial Fe-Cl distance of 2.232(2) Angstrom and in-plane Fe-N distances averaging 2.082 Angstrom is consistent with its high spin (S = 5/2) character. This monomer is readily converted to the green {Fe-III(trans-OEPO(2))}O-2 using aqueous hydroxide. {Fe-III(trans-OEPO(2))}O-2 crystallizes in the monoclinic space group C2/c with a = 23.541(8) Angstrom, b = 15.392(5) Angstrom, c = 18.686(8) Angstrom, and beta = 90.09(3)degrees at 294 K with Z = 8. Refinement of 3472 reflections with F > 6.0 sigma(F) and 393 parameters yielded R = 0.0484, R(w) = 0.0527. The complex possesses a crystallographically imposed 2-fold symmetry axis that passes through the oxo ligand. The dioxoporphodimethene ligands within the molecule are roof-shaped and fold away from each other. The axial Fe-O distance is 1.749(1) Angstrom with longer in-plane Fe-N distances (average 2.077 Angstrom).The Fe-O-Fe angle of 165.4(2)degrees deviates significantly from Pyridine solutions of either the iron(III) monomer or mu-oxo dimer autoreduce over a period of days to give (py)(2)Fe-II(trans-OEPO(2)). This red compound crystallizes in the space group P2(1) with a = 19.177(4) Angstrom, b = 20.039(4) Angstrom, c = 10.547(2) Angstrom, and beta = 100.36(3)degrees at 130 K with Z = 2. Refinement of 5090 reflections with one restraint and 984 parameters yielded R1 = 0.0684, wR2 = 0.1763. The complex crystallizes with two distinct molecules in the asymmetric unit; each molecule contains a different degree of disorder with respect to the trans meso oxygen atoms (50/50, 71/29). Each independent molecule exhibits severe ruffling of the macrocycle. The six coordinate iron(II) center is diamagnetic. The axial Fe-N(pyridine) distances average 1.98 Angstrom, and the in-plane Fe-N(pyrrole) distances average 1.95 Angstrom. A common trend observed for the dioxoporphodimethene macrocycle in all of these structures is an elongation toward the trans oxidized meso carbons. These complexes were originally prepared as cis and trans isomeric mixtures that can be enriched in the trans isomer by fractional crystallization. This is evident in their distinctive H-1 NMR spectra. In addition, these compounds are characterized by electron impact mass spectrometry and UV-visible, ESR, and infrared spectroscopies.