Mössbauer studies on protoporphyrin IX iron(II) solutions

Abstract

Mössbauer spectroscopic studies on frozen solutions of protoporphyrin IX iron(II) in the pH range 7–14 reveal evidence for three different species. The species dominant over the pH range 7–13 is a polymeric species (A) made up of a bare protoporphyrin IX iron(II) moieties, the number of moieties in the polymer is discussed relative to concentration and pH. This species is assigned an S = 1 spin state. Above pH 13 a high spin iron(II) species (C) is present. The quadrupole splitting associated with this species is discussed and is the largest yet reported for an iron(II) propoporphyrin. This species (C) is a five coordinate protoporphyrin IX iron(II) with a hydroxide ion as the fifth ligand. The third species (B) is a minor constituent of this system and also has a high spin iron(II) structure, though the Mössbauer parameters for this site are more in keeping with a distorted octahedral environment.