Magnetism of ferriprotoporphyrin IX monomers and dimers

The SQUID and the 57Fe Mössbauer spectroscopy studies of the magnetic properties of monomeric and dimeric forms of iron porphyrin were performed between 2 and 305 K. The effective magnetic relaxation rate of the Fe atoms in iron porphyrin monomers exhibits complex temperature dependence, resulting from the competing spin–spin and spin-lattice relaxation processes. The dimerization of iron porphyrin dramatically speeds up the magnetic relaxation. The Fe–Fe antiferromagnetic exchange coupling constant in Fe–O–Fe dimer is J≈−110 cm−1. The complementary application of SQUID and the Mössbauer spectroscopy is proposed as a new precise quantitative analytical methodology for monitoring of the aggregation process of iron porphyrin.