31P NMR study of the valence stability of tin in its 1-hydroxyethylene-diphosphonate (HEDP) and N,N′,N′-trimethylenephosphonate-polyethyleneimine (PEI-MP) complexes

Abstract The valence stability of tin in its complexes with 1-hydroxyethylene-diphosphonate (HEDP) and with N , N ′, N ′-trimethylenephosphonate-polyethyleneimine (PEI-MP) was investigated. With particular interest in the possible interconversion between Sn 2+ and Sn 4+ , the complexes were monitored with the aid of 31 P NMR spectroscopy. The extent of complex formation with both ligands was evaluated for systems with tin in their respective oxidation states. The Sn 2+ -complexes underwent initial, but limited oxidation upon preparation, and beyond which were rather stable, irrespective of pH or time. Both Sn 2+ - and Sn 4+ -complexes were found to exist in solution without change. Oxidation of Sn 2+ was achieved by addition of hydrogen-peroxide and was partially reversed by the addition of glutathione (GSH). The amount of H 2 O 2 needed for complete oxidation of the Sn 2+ - into Sn 4+ -complexes was determined for both ligands, as well as the time taken for that oxidation.