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

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 Sn2+ and Sn4+, 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 Sn2+-complexes underwent initial, but limited oxidation upon preparation, and beyond which were rather stable, irrespective of pH or time. Both Sn2+- and Sn4+-complexes were found to exist in solution without change. Oxidation of Sn2+ was achieved by addition of hydrogen-peroxide and was partially reversed by the addition of glutathione (GSH). The amount of H2O2 needed for complete oxidation of the Sn2+- into Sn4+-complexes was determined for both ligands, as well as the time taken for that oxidation.

31P NMR study to determine the extent of oxidation – if any – of divalent tin when complexed with diphosphonate 1-hydroxyethylene-diphosphonate (HEDP) and polyphosphonate N,N′,N′-trimethylenephosphonate-polyethyleneimine (PEI-MP), respectively. In so doing evaluating the valence stability of complexed tin and the possibility of interconversion between tin(II) and tin(IV).Figure optionsDownload as PowerPoint slide