Coordination chemistry of bis-thiohydroxamic acids: synthesis and characterization of their lead(II) complexes and stability constant determination

Abstract

The synthesis of a number of bis-thiohydroxamic acids with linking groups of varying lengths and rigidities are reported as potential Pb 2+-specific chelating agents. In contrast to the predictions of CaChe® and CAVAET© molecular mechanics programs, the most rigid ligands of this series do not form discreet Pb 2+ complexes, but rather polymers. The less rigid aliphatic linking groups do form discreet complexes with Pb 2+, which are characterized by 1H, 13C and 207Pb NMR. The synthesis and X-ray crystal structure of the first water-soluble bis-thiohydroxamic acid, N-hydroxy-3{2-[2-(hydroxy-methyl-thio-carbamoyl)ethoxy]ethoxy}- N-methy thiopropionamide ( 11) is described. The structure of 11 shows that the thiohydroxamic groups in the molecule adopt a Z configuration and form weak intermolecular hydrogen bonds resulting in a chain structure in the solid state. The formation constant of 11 with Pb 2+ in 50% methanol/water is found to be 10 12.53.