Mössbauer studies on tetra(p-sulphophenyl)porphine iron(III) solutions

The Mössbauer spectra of frozen aqueous solutions of iron(III) over the pH range 1.9 to 12 are reported. The spectra show that tetra(p-sulphophenyl)porphine iron(III) exists principally in two forms, monomeric and as μ-oxo-oligomers, depending on the pH of the solution. Above pH 4.0 only the μ-oxo-oligomer exists and at very low pHs (2.0 or less) only monomers are present. The quadrupole splitting of the monomer is the largest yet recorded for a five coordinate high spin iron(III) porphyrin.