Inter-Ring Interactions in [Fe(TalkylP)(Cl)] (alkyl = ethyl, n-propyl, n-hexyl) Complexes: Control by meso-Substituted Groups

Intermolecular Interactions and Intramolecular Couplings of Binuclear Porphyrin Models for Cytochrome c Oxidase

Cytochrome c oxidase (CcO) has a binuclear active site composed of a high-spin heme group and a tris-histidine-ligated copper ion (Cu_B). By using two different porphyrin models derived by Gunter (H₂TPyPP) and us (H₂TImPP), we have isolated several mono- and binuclear complexes including one carbonyl and three chloride derivatives which are determined by 100 K single-crystal X-ray. Low-temperature (4 K) EPR and multitemperature (295-25 K) Mössbauer investigations on the products not only confirmed the spin states of the two metal ions (S = 5/2 Fe³⁺ and S = 1/2 Cu²⁺) but also revealed the intermolecular interactions and intramolecular couplings which are in accordance with the crystal structural features.

Effect of the Ruffled Porphyrin Ring on Electronic Structures: Structure and Characterization of [Fe(TalkylP)(OClO3)] and [Fe(TPrP)(THF)2]ClO4 (alkyl = Ethyl, Et and n-Propyl, Pr)

We report the synthesis of Fe(TalkylP)(OClO3)] (alkyl = ethyl and propyl) and [Fe(TPrP)(THF)2]ClO4, which are characterized by UV-vis, EPR, X-ray crystallography, and solid-state magnetic susceptibilities. The macrocycles of all three complexes are ruffled, all of the structural features for [Fe(TEtP(OClO3)] and [Fe(TPrP)(OClO3)] are characteristic of the nearly pure S = 3/2 state, while the structural parameters for [Fe(TPrP)(THF)2]ClO4 feature a pure intermediate-spin (S = 3/2) state, which are all consistent with EPR and magnetic data. It is clear from these studies that the ruffled conformation plays a significant role in affecting the extent of S = 3/2 character.

Metalloporphyrin mixed-valence π-cation radicals: [Fe(oxoOEC(•/2))(Cl)]2SbCl6, structure, magnetic properties, and near-IR spectra

The preparation and characterization of a mixed-valence π-cation radical derivative of an iron(III) oxochlorinato complex is reported. The new complex has been synthesized by the one-electron oxidation of a pair of [Fe(oxoOEC)(Cl)] molecules to form the dimeric cation [Fe(oxoOEC)(Cl)]₂⁺. The cation has been characterized by X-ray analysis, Mössbauer spectroscopy, UV-vis and near-IR spectroscopy, and magnetic susceptibility measurements from 6-300 K. The crystal structure shows that the two rings have a smaller overlap area than those of the formally related nickel and copper octaethylporphinate derivatives, reflecting the larger steric congestion at the periphery in part of the oxochlorin rings. The Mössbauer data is consistent with two equivalent iron(III) centers. The unpaired electron is delocalized over the two oxochlorin rings and mediates a strong antiferromagnetic interaction between the high-spin iron(III) centers.

Structural and magnetic effects of meso-substitution in alkyl-substituted metalloporphyrinate pi-cation radicals: characterization of [Fe(TalkylP*)(Cl)]SbCl6 (alkyl = ethyl and n-propyl)

We report the preparation and characterization of two meso-alkyl substituted porphyrin pi-cation radical derivatives, [Fe(TalkylP(*))(Cl)]SbCl(6) (alkyl = ethyl or propyl). Both complexes have been characterized by UV/vis/near-IR, IR, and Mossbauer spectroscopy, temperature-dependent solid-state magnetic susceptibility measurements, and X-ray structure determinations. All data for both oxidized species are consistent with the formulation of the complexes as ring-oxidized iron(III) porphyrin species. The molecular structures of the two five-coordinate species have the typical square-pyramidal coordination group of high-spin iron(III) derivatives. The crystal structures also reveal that the species form cofacial pi-pi dimers with lateral shifts of 1.44 A and 3.22 A, respectively, for the propyl and ethyl radical derivatives. Both radicals exhibit porphyrin cores with alternating bond distance patterns in the inner 16-membered ring. In addition, [Fe(TEtP(*))(Cl)]SbCl(6) and [Fe(TPrP(*))(Cl)]SbCl(6) have been characterized by temperature-dependent (6-300 K) magnetic susceptibility studies, the best fitting of the temperature-dependent moments reveal strong coupling between iron spins and porphyrin radical, and a smaller magnitude of antiferromagnetic coupling between ring radicals, which are opposite to those found in the five-coordinate iron(III) OEP radicals. The differences in structure and properties of the cation radical meso-alkyl and beta-alkyl derivatives possibly reflect differences in properties of a(1u)- and a(2u)-forming radicals.