Electrospray ionization mass spectrometry in the structural characterization of some diphenyllead(IV) thiosemicarbazonates

The behavior in electrospray ionization mass spectrometry (ESI-MS) conditions of some complexes formed by Pb(C6H5)(2)(OAC)(2) with salicylaldehyde, 2-ketobutyric acid, pyridine-2-carbaldehyde, 2-acetylpyridine, and 2-benzoylpyridine thiosemicarbazones, was studied in detail with the aid of collisional experiments performed by ion trap. The homoleptic complexes of tridentate thiosemi-carbazonate dianions (TSC2-) lose the phenyl groups first, destabilizing the high oxidation state of the metal and leading to Pb(II) complexes in which the TSC2- ligand or a part of it remains coordinated to the metal. The main difference among the complexes derives from the presence of a carboxylate group on the 2-ketobutyric acid thiosemicarbazonato ligand, which probably interacts with a Na+ cation leading to ESI-generated [M+Na](+) species. In the absence of the carboxylate group, the production of abundant protonated molecules is observed. These different behaviors have been rationalized from the structural point of view. The heteroleptic mononuclear complexes, including thiosemicarbazonate and AcO- monoanions in the coordination sphere, do not yield intact ionized molecular species, and the most abundant ESI-generated ion is due to AcO- loss. The spectrum of the binuclear heteroleptic complex formed by the salicylaldehyde thiosemicarbazonate monoanion is conditioned by the weak bonding interaction displayed by the acetate bridge. MSn experiments yield important information on the relative ligand-Pb bond strengths. This work forms part of the search for chelating agents that can be used for effective chemotherapy of organolead poisoning. Copyright (C) 2004 John Wiley Sons, Ltd.