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 31P 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 2O 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.