Evidence for Interfacial Molecular Recognition in Transition Metal Complexes Adsorption on Amorphous Silica Surfaces

A series of Ni(II) complexes containing polyamines and 1, 2, or 3 labile aqua ligands ([Ni(en)(dien)(H 2 O)] 2+, [Ni(en) 2 (H 2 O) 2 ] 2+, [Ni(dien)(H 2 O) 3 ] 2+ ) were selectively adsorbed on the same silica support. In all cases, saturation coverages derived from adsorption isotherms were far below one physical monolayer and UV−visible and EXAFS spectroscopy suggested adsorption by grafting on specific surface sites. The density of adsorption sites was different for all three complexes, suggesting that molecular recognition phenomena, probably implying interactional complementarity between surface and adsorbate, are operative in the adsorption mechanism.