Mössbauer, magnetic susceptibility, and EPR studies of intermediate spin iron (III) dithiooxalato halides

Mössbauer, magnetic susceptibility, and EPR measurements have been performed in the series of intermediate spin [Fe(S2C2O2)2X]2−, (X=Cl, Br, I) complex anions. All members of the series are paramagnetic down to 1.4 °K. Mössbauer and EPR results establish the axial character of the electronic spin Hamiltonian for the iodide derivative and increasing rhombicity for Br and Cl. Axial zero field splitting parameters D are positive and near 5 °K. The quadrupole splittings are large in the range 3.4–3.6 mm/sec and typical for the S=3/2 state of Fe(III). Isomer shifts are near 0.30 mm/sec indicating substantial d electron delocalization in the π system of the ligand. The magnetic hyperfine constant decreases from the Cl to the I derivative indicating increasing covalency of the metal–halide bond. Pronounced relaxation effects are present in the Mössbauer spectra varying with the halogen ligand. Spectra in applied fields up to 60 kG have seen fitted with a relaxation theory based on a stochastic model.