Unusual relaxation phenomena in the ⁵⁷Fe Mössbauer spectra of FeX₃ (X = Cl, NO₃, ClO₄, MnO₄, 1/2(S₂O₈)) complex salts containing urea, methylated urea, chlorido or aquo ligands: studies on the influence of the ligand sphere and deuteration

Mössbauer spectra of Fe^III complex salts with urea-related ligands show a broadened line due to magnetic relaxation. The origin of the relaxation is not known, mostly spin–spin type is considered. A study of a large number of compounds can be helpful to show differences in the Mössbauer parameters and to see the infuence of the chemical environment on the relaxation. We have evaluated the Mössbauer spectra of 13 compounds recorded at various temperatures with the Blume–Tjon two-state relaxation model and with the (unrestricted) Afanasev–Gorobchenko model. The latter showed significant differences between some salts, and proved the presence of spin–lattice relaxation.