COORDINATION CHEMISTRY OF BIS-THIOHYDROXAMIC ACIDS - SYNTHESIS AND CHARACTERIZATION OF THEIR LEAD(II) COMPLEXES AND STABILITY CONSTANT DETERMINATION

The syntheses of a number of bis-thiohydroxamic acids with linking gro ups of varying lengths and rigidities are reported as potential Pb2+-s pecific chelating agents. In contrast to the predictions of CAChe(R) a nd CAVAET(C) molecular mechanics programs, the most rigid ligands of t his series do not form discreet Pb2+ complexes, but rather polymers. T he less rigid aliphatic linking groups do form discreet complexes with Pb2+, which are characterized by H-1, C-13 and Pb-207 NMR. The synthe sis and X-ray crystal structure of the first water-soluble bis-thiohyd roxamic acid, roxy-methyl-thio-carbamoyl)ethoxy]ethoxy}-N-methyl thiop ropionamide (11) is described. The structure of 11 shows that the thio hydroxamic groups in the molecule adopt a Z configuration and form wea k intermolecular hydrogen bonds resulting in a chain structure in the solid state. The formation constant of 11 with Pb2+ in 50% methanol/wa ter is found to be 10(12.53).