Amorphous Silica as a Versatile Supermolecular Ligand for NiII Amine Complexes: Toward Interfacial Molecular Recognition

Abstract Selective adsorption of Ni II amine complexes used as precursors for supported catalysts was studied on amorphous silica surfaces. The nature of the adsorption sites was probed by [Ni(en)(dien)(H 2 O)] 2+ , [Ni(en) 2 (H 2 O) 2 ] 2+ , and [Ni(dien)(H 2 O) 3 ] 2+ (en=ethylenediamine, dien=diethylenetriamine), which respectively contain one, two, and three labile aqua ligands. The silica surface acts as a mono‐ or polydentate ligand that can substitute the aqua ligands of the Ni II complexes in an inner‐sphere adsorption mechanism. Room‐temperature adsorption isotherms indicate that each nickel complex selects a limited number of adsorption sites; different sites are recognised by the three complexes, even though they have the same charge and comparable sizes. Several spectroscopic techniques (UV/Vis/NIR, EXAFS, and 29 Si NMR) were used to confirm the selective character of the interaction of Ni II amine complexes with the silica surface. The specific sites include both silanol/silanolate groups in the same number as the original labile ligands and other surface groups that probably act as hydrogen‐bond acceptors. These two types of groups cooperate to result in interfacial molecular‐recognition phenomena with interactional complementarity.