Abstract

The reaction of 2-[3-(triethoxysilyl)propylamino]ethanethiol (LH, a) and 1-methyl-2-[3-(triethoxysilyl)propylamino]ethanethiol (LH, b) with ZnX₂ and CdX₂ (X = Cl, Br, I, NO₃) in tetrahydrofuran (THF) or CH₂Cl₂ gives several complexes depending on the experimental conditions. Elemental analyses, IR, Raman, ¹³C{¹H}, ¹H NMR and mass spectroscopies indicated the formation of mononuclear and dinuclear complexes. In the absence of NEt₃ as proton quencher, the protonated ligands react in their zwitterionic form giving dinuclear [M(LH)X₂]₂ [M = Zn (1), Cd (2); LH = a, b; X = Cl, Br, I] or mononuclear M(NO₃)₂(LH)₂ [M = Zn (5), Cd (6); LH = a] complexes. In both cases, coordination occurs through the S atoms, the ligands acting as terminal and bridging species. With NEt₃, the deprotonated ligands are chelated through their N and S atoms and bridging occurs through the S atoms in [MLX]₂ [M = Zn (3), Cd (4); LH = a; X = Cl, Br] complexes. The LH ligand is chemically grafted onto silica, the procedure optimized and the resulting material characterized by ¹³C and ²⁹Si cross-polarization, magic-angle spinning (CP-MAS) NMR and DRIFT. This material is evaluated as a supported molecular trap for binding heavy metals (Cd²⁺, Hg²⁺, Pb²⁺) in aqueous solution. In both batch and column processes, it appears that Hg²⁺ and Pb²⁺ are trapped more than Cd²⁺, but in all cases values lower than those allowed were obtained.