Mossbauer studies in transition metal chemistry. III. Compounds of iron with some sulphur-containing Schiff base ligands

M�ssbauer spectra are reported for a series of iron complexes with sulphur-containing Schiff base ligands. These tridentate ligands are based on the Schiff base formed by the condensation of dithiocarbazic acid and pyridine-2-carbaldehyde and form complexes with a metal-to-ligand ratio of 1 : 1 and 1 : 2. The M�ssbauer study confirms that most of these complexes contain iron(11) with examples of both high-and low-spin and one example of a spin crossover. Several iron(111) complexes were also studied. The quadrupole splittings show the anisotropy in bonding expected for metal atoms coordinated to different types of atoms within the same chelate ring. However, for some complexes the splittings are small, showing that low local symmetries need not produce large electric field gradients. In cases where it is applicable, the temperature dependence of the quadrupole splitting has been used to derive a splitting of the t2 and e orbitals produced by the non-cubic symmetry. For compounds of the form Fe(L)X2, where X is a halide and L the tridentate ligand, the Mossbauer results are best interpreted in terms of a five-coordinate structure rather than a six-coordinate bridged dimer.