Electron paramagnetic resonance studies of low-spin d5 transition metal complexes

Ferric species of the giant extracellular hemoglobin of Glossoscolex paulistus as function of pH: An EPR study on the irreversibility of the heme transitions

“…Therefore, the heme avoids a classic Jahn-Teller effect, with the axial ligands preferring the perpendicular orientation, which shows smaller orbitals overlap with the iron orbitals than the parallel orientation, causing a smaller splitting of iron d orbitals. In fact, Rieger (1994) has reported that Type I hemichrome presents an apparent neardegeneracy of the d xz and d yz orbitals that is consistent with the crystal structure, which showed that the two ligands lie in perpendicular planes because of the similar orbitals overlap to d xz and d yz .…”

Ferric species equilibrium of the giant extracellular hemoglobin of Glossoscolex paulistus in alkaline medium: HALS hemichrome as a precursor of pentacoordinate species

“…This weakness would decrease the stability of these ligands in the first coordination sphere of iron originating the rupture of at least one histidine from the iron ion, promoting the pentacoordinate ferric species formation. Rieger [59] has reported that Type I hemichrome presents an apparent near-degeneracy of the d xz and d yz orbitals that is consistent with various heme protein crystal structures, which showed that the two axial ligands lie in perpendicular planes because of the similar orbitals overlap of the d xz and d yz with the orbitals from the ligands.…”

Further Studies on the Oxidation State of Iron in μ-Oxo Dimeric Phthalocyanine Complexes

“…In this case the two Fe(III) centers would be practically independent of each other and the wellknown ESR spectra for hexacoordinated monomeric low-spin Fe(III) complexes can be expected [78]. However, neither Ercolani et al [17] nor we could record ESR spectra of form '627' in solutions at room temperature or in frozen solutions at 77 K. If Fe(II) ions are supposed to be present in both forms '690' and '627' no ESR spectra would be expected [63,76].…”