The visible and infrared spectroelectrochemistry of the redox chemistry of Co-II-porphinone complexes were examined and compared with similar studies of the respective iron complexes. Cobalt(II) porphinone complexes undergo a one-electron reduction and two one-electron oxidations within the potential region that was studied in this work. The one electron spectroelectrochemical reduction of Co-II(P) (P = octaethylporphyrin (OEP), octaethylporphinone (OEPone), and octaethylporphinedione (OEPdione)) were studied using visible spectroscopy, and their cobalt(I) complexes were characterized. The same reduction was examined by FTIR spectroscopy for P = OEPone and OEPdione. The infrared spectra showed downshifts of the nu(CO) band that were consistent with a cobalt(I) complex and were similar to the iron(I) complex. The two one-electron oxidations of Co-II(OEPone) and Co-II(OEPdione) were also carried out using visible and infrared spectroelectrochemistry. The nu(CO) band for cobalt was less sensitive to the metal oxidation state (III vs. II) than was observed in the iron complexes. Additional upshifts in the nu(CO) band were observed for the pi-cation radical. Isotopic O-18 substitution on the carbonyl group of the H(2)OEPone was done in order to determine the degree of mixing up the porphinone modes with the carbonyl vibrations. (C) 2012 Elsevier B.V. All rights reserved.