Schiff base chelate-functionalized organoclays

An amine-functionalized layered magnesium silicate (Mg-APTES) was prepared by direct alkaline co-polymerization between magnesium chloride and 3-aminopropyltriethoxysilane. Solid state 13C and 29Si NMR and elemental analyses reveal a partial condensation of the framework precursors. The X-ray diffraction pattern shows a disorganized talc-like structure with a basal spacing consistent with the presence of interdigitated and slightly titled organic moieties in the interlayer galleries. The surface primary amines of Mg-APTES were further reacted separately with several aldehydes (salicylaldehyde, 5-chlorosalicylaldehyde, 2-pyridine carboxyaldehyde) and one ketone (acetylacetone) in order to form Schiff base chelating ligands with O- and N-donor groups incorporated in the layer surface. The successful formation of the chelating groups on the surface was determined by the observation of imine IR vibration bands in the 1600–1645 cm−1 range, and confirmed by solid state 13C NMR. Powder X-ray diffraction patterns of the Schiff base-modified compounds show that the layered structure is maintained with an expansion of the interlayer space consistent with the steric size of the chelating groups. Transition metal ions (Cu2+, Ni2+, Co2+) were incorporated into the chelate-modified organoclays. The UV–visible and ESR data of a representative sample prepared by Cu2+ ion complexation correlate reasonably well with those of the analogous Cu(II)Salpn complex (Salpn = bis(salicylidene)propylendiamine), indicating the formation of anchored Schiff base-type complexes.