The study of the ground state Kramers doublet of low-spin heminic system revisited: A comprehensive description of the EPR and Mössbauer spectra

A general study of the ground state Kramers doublet of FeIII in the low-spin configuration using the hole formalism is presented. This description allows a generalization of Taylor equations that relate g-values of iron to the wave function of the unpaired electron and the energy separation between the t2g orbitals. Expressions for the Fe-hyperfine tensor and valence contribution to the 57Fe nuclear quadrupolar interaction are also obtained for the general case. The model is connected with the counter-rotation effect described in heme systems, which appears in the formulation as a particular case. A procedure to analyze data from EPR and Mössbauer spectroscopic techniques together is presented. It lets us distinguish between the two essentially different solutions derived when only EPR data are available. The model is applied to experimental results available in the literature.