Structure, absolute configuration and electrochemical properties of Tris(N-methylformothiohydroxamato)iron(III), an antibacterial metal chelate and potential iron siderochrome

Abstract

The title compound, which previously had been isolated from bacteria and shown to possess anti-bacterial activity, has been chemically synthesized. The molecular structure has a cis (facial) arrangement of the asymmetric {S,O} bidentate ligands (Fe-S 2.441(1) Ǻ, Fe-O 2.010(1) Ǻ) as required by the crystallographic C₃ molecular symmetry. (Crystal data: C₆H₁₂N₃O₃S₃Fe, rhombohedral, space group R3, a 7.094(2)Ǻ, α 102.00(1)°, Z 1.) The complex was spontaneously resolved into enantiomers on crystallization and the absolute configuration in the crystal studied was established as Λ by the anomalous dispersion technique. Magnetic, e.s.r. and Mossbauer studies are compatible with a distorted octahedral complex of high-spin iron(III). Cyclic voltammetric studies in acetone of the title compound and some related iron(III) thiohydroxamates were carried out. A reversible Fe^III/Fe^II reduction wave was observed for the N-methylformothiohydroxamato chelate, in contrast to the irreversible reduction of tris(benzohydroxamato)iron(III), a related complex containing an {O,O} chelate. The tris(benzothiohydroxamato) chelate, Fe(PhC(S)NHO)₃, which possesses a non-alkylated nitrogen, also showed an irreversible reduction wave.