Coordination ability of free or silica immobilized Schiff bases towards Hg(II), Cd(II) and Pb(II) ions

A series of ligands, consisting of Schiff bases and their reduced amine derivatives, was prepared by [2+1] condensation of 3-methoxy (or 3-ethoxy)-2-hydroxybenzaldehyde or 2-hydroxybenzaldehyde with 3,4-diaminobenzoic acid or 1,2-diaminobenzene, and by subsequent reduction with hydrogen or NaBH4. The complexation behavior of these ligands towards Cd(II), Pb(II) and Hg(II) salts was tested and the resulting complexes characterized by elemental analysis, IR and NMR spectroscopy, ESI-MS mass spectrometry and SEM–ESEM microscopy. Ligand-bearing silicas were prepared by the reaction of a carboxylic group at the periphery of the coordinating moiety of the Schiff bases or amine derivatives with functionalized silicas bearing NH2 or Cl groups. Ligand-bearing silicas were characterized by elemental analysis, IR spectroscopy and SEM–ESEM microscopy. Finally, the capability of these materials to sequestrate the above mentioned metal ions from water solutions was studied. Preliminary data on the selective recognition of mercury ions from cadmium and lead ions are reported.