Magnetic circular dichroism (MCD) spectra are reported for [5,10,15,20-tetrakis(l-methylpyridinium-4-yl)porphinato]iron(III) and -iron(II), FeIII TMP and FeIITMP, and some of their derivatives in the near-UV to near-IR regions. Two proton equilibria existed between the three FeIIITMP monomers with pKa values of ca. 5.7 and 12.3 while, after electrochemical reduction, an equilibrium was observed between the two FeIITMP monomers with a pKa of ca. 11.2. The species were in high-spin states except FeIIITMP at pH >13 and FeIITMP at pH >12 (low spin). Porphyrin electronic structures of the coordination spheres on these species and their bis(imidazole) and bis(cyanide) derivatives are discussed in comparison with information on iron porphyrins and hemes previously studied.
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