Thiohydroxamato complexes of iron(III). Synthesis, magnetism and Mössbauer spectra

Abstract

The syntheses of thiohydroxamic acid ligands and their iron(III) complexes are described in detail. The tris-chelates are of particular importance because of their relation to one such complex which is thought to be involved in bacterial iron-transport systems. Magnetic and spectral measurements show that the tris-chelates generally display high-spin behaviour similar to that exhibited by corresponding hydroxamato complexes. Variable temperature magnetic and Mossbauer measurements on samples of the tris(benzothiohydroxamato) derivative confirm earlier postulates of spin-crossover behaviour for this compound, with a low-spin (S 1/2 or 3/2) component at low temperatures of c. 8%. Efforts to obtain crystal structures on a tris(thiohydroxamato)iron(III) complex have been thwarted by twinning effects and by powder-like formation within well formed crystal faces. The molecular structure of these, and of the related cobalt(III) chelates, most likely contains the cis (facial) isomer.     A new series of bis-chelates, FeL₂Cl, has also been prepared and physical measurements show high-spin iron(III) behaviour.