INSITU XANES OF AN IRON PORPHYRIN IRREVERSIBLY ADSORBED ON AN ELECTRODE SURFACE

In situ iron K-edge X-ray absorption near edge structure, XANES, has been employed to examine the axial coordination of (mu-oxo)bis[iron meso-tetrakis(4-methoxyphenyl)porphyrin] (FeTMPP)2O, irreversibly adsorbed on a high area carbon substrate, Black Pearl (BP), as a function of applied potential. Analysis of the XANES provides conclusive evidence that the coordination about Fe3+ in the supported, fully oxidized macrocycle is remarkably different from that about Fe2+ in the corresponding fully reduced macrocycle. In the adsorbed, oxidized state, (FeTMPP)2O retains its mu-oxo character and it undergoes a two-electron reduction to yield predominantly four-coordinate square-planar FeTMPP without axial ligation.