Addressing Lead Toxicity:  Complexation of Lead(II) with Thiopyrone and Hydroxypyridinethione O,S Mixed Chelators

The lead(II) ion is regarded as a serious environmental contaminant. A considerable need exists to develop selective ligands for remediation of this metal ion. Herein, the coordination chemistry of lead(II) is investigated with three O,S donor ligands: thiomaltol, 3-hydroxy-1-methyl-2(1H)-pyridinethione (3,2-HOPTO), and 3-hydroxy-1,2-dimethyl-4(1H)-pyridinethione (3,4-HOPTO). The X-ray structures of [Pb(thiomaltolato)2] and [Pb(3,4-HOPTO)2] have been solved, revealing the expected 4-coordinate geometries. Electronic spectra have been obtained for the lead(II) complexes with all three ligands. Preliminary solution studies show that the thiomaltol ligand binds lead(II) preferentially over magnesium(II) and calcium(II); however, [Pb(thiomaltolato)2] is not stable in the presence of 1 equiv of EDTA. Tetradentate ligands derived from these O,S chelators are expected to generate higher affinity ligands for lead(II) sequestration.