Crystal structure and magnetic behaviour of a five-coordinate iron(III) complex of pyridoxal-4-methylthiosemicarbazone

The crystal structure and magnetic properties of a penta-coordinate iron(III) complex of pyridoxal-4-methylthiosemicarbazone, Fe(H₂mthpy)Cl₂](CH₃C₆H₄SO₃), are reported. The synthesised ligand and the metal complex were characterised by spectroscopic methods (¹H NMR, IR, and mass spectroscopy), elemental analysis, and single crystal X-ray diffraction. The complex crystallises as dark brown microcrystals. The crystal data determined at 100(1) K revealed a triclinic system, space group (Z = 2). The ONSCl₂ geometry around the iron(III) atom is intermediate between trigonal bipyramidal and square pyramidal (τ = 0.40). The temperature dependence of the magnetic susceptibility (5-300 K) is consistent with a high spin Fe(III) ion (S = 5/2) exhibiting zero-field splitting. Interpretation of these data yielded: D = 0.34(1) cm⁻¹ and g = 2.078(3).