COORDINATION CHEMISTRY OF MICROBIAL IRON TRANSPORT .45. SYNTHESIS AND CHARACTERIZATION OF CHIRAL ISOMERS OF TRIS(1-OXO-22(1H)-PYRIDINETHIONATE)IRON(III), CHROMIUM(III), AND COBALT(III) COMPLEXES

Among the chelating functional groups found in the microbial iron-transport agents called siderophores are hydroxamate, catecholate, and thiohydroxamate. The synthesis and properties of several chiral ligands containing 1-hydroxy-22(1H)-pyridinethione are reported. The synthesis and properties of ferric, chromic and cobaltic complexes of these ligands are reported as well. The Cr(III) and Co(III) complexes give electronic absorption spectra which show the two expected d-d transition for d3 and low-spin d6 octahedral complexes superimposed on very broad ligand transitions. Two absorption maxima are also seen in the electronic spectra of the ferric complexes, and which appear to be charge transfer transitions. These spectra resemble those of corresponding thiobenzohydroxamate complexes. Since the ligands are chiral, four diastereomers are possible, but only one isomer has been observed for each complex. All complexes seem to have the cis (or facial) geometry, with C3 point symmetry, and both configurations. LAMBDA and DELTA, have been observed. The chirality of the complexes is assigned based on the signs of the CD bands of the low-energy transition in CR(III) and CO(III) d3 low-spin d6 systems, respectively, and by comparing the shape and signs of CD bands of these complexes with those of the resolved optical isomers of tris(thiobenzohydroxamato)iron(III), chromium(III) and cobalt(III).