One-electron oxidized product of difluoroiron(iii) porphyrin: is it iron(iv) porphyrin or iron(iii) porphyrin π-cation radical?

Abstract

The electronic structure of [Fe(TMP)F₂], which is formally a one-electron oxidation equivalent above [Fe^III(TMP)F₂]⁻, has been examined in solution by ¹H NMR, UV-Vis, and Mössbauer spectroscopy. In CD₂Cl₂–CD₃OD solution at 193 K, the pyrrole-H and m-H signals appeared at 128.2 and 116.7 ppm, respectively. The UV-Vis spectrum showed broad absorption bands at 560–680 nm. The Mössbauer spectrum taken in frozen toluene–methanol solution exhibited a very broad single line from which the IS and QS values were determined by computer simulation to be 0.50 and 0.14 mm s⁻¹, respectively. On the basis of these results, it was concluded that the one-electron oxidized product of [Fe(TMP)F₂]⁻ should be formulated as the iron(III) radical cation [Fe^III(TMP˙)F₂], not as iron(IV) porphyrin [Fe^IV(TMP)F₂] as previously suggested.