ABSORPTION AND MAGNETIC CIRCULAR-DICHROISM SPECTROSCOPY OF METAL-OXIDIZED AND RING-OXIDIZED PORPHYRINS - SPECTRAL CHARACTERISTICS OF THE ONE-ELECTRON AND 2-ELECTRON OXIDATION-PRODUCTS OF COBALT OCTAETHYLPORPHYRIN

One- and two-electron oxidation products of cobalt(II) octaethylporphyrin, CoIIOEP(-2), have been characterized by optical absorption and MCD spectroscopy. One-electron oxidation leads either to the metal-oxidized complex, [CoIIIOEP(-2)]X, or to the porphyrin-ring-oxidized species, [CoIIOEP(-1)]*+X-, depending on the ligand, X-, that is present. With X- = Cl-, Br-, and SbCl6-, metal oxidation is observed, while with X- = ClO4-, ring oxidation takes place. The spectral properties of the cation-radical species, [ComOEP(-l)]*2+(X)2, that are formed following the two-electron oxidation of CoOEP(-2) vary significantly for the Cl-, Br-, ClO4-, and SbCl4- counterions. The differences between the spectral properties of a range of oxidized complexes have been investigated by using deconvolution analysis of the absorption and MCD spectra to provide quantitative information about the energies of bands that contribute to the observed spectral envelope. The relationship between the spectroscopic data and the two possible radical ground states, 2A1U or 2A2u, that are accessible to the porphyrincation-radical species is discussed. The patterns of bands that are characteristic of the 2A1U or the 2A2u ground states for the cation-radical species are described by comparing the absorption and MCD spectral data formed by ring oxidation of zinc tetraphenylporphyrin and magnesium octaethylporphyrin to the cation-radical complexes [ZnTPP(-1)]+ and [MgOEP(-1)]+ with the data from the CoOEP complexes. The MCD spectral data show that ring oxidation always leads to the appearance of characteristic spectral features in the visible region that can be used as a fingerprint for ring oxidation compared with metal-based oxidation. This spectral envelope is observed for both the Co(II) and Co(III) cation-radical complexes. © 1990, American Chemical Society. All rights reserved.