Amorphous Silica as a Versatile Supermolecular Ligand for Ni^II 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) (H2O)]2+, [Ni(en)2(H2O)2]2+, and [Ni(dien)(H2O)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 29Si 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.

Confinement in Nanopores at the Oxide/Water Interface: Modification of Alumina Adsorption Properties

“…In fact, Boujday et al have shown that a complete description of adsorption sites for Ni-ethylenediamine complexes on silica requires that the cooperative formation of hydrogen bonds between the Ni II complex and the surface (interactional complementarity) through the interaction of NH groups from ethylenediamine (hydrogen donors) and surface oxygen atoms (hydrogen acceptors) is taken into account. [20] Moreover, it is recognised that the solvent may perturb the intermolecular hydrogen-bonding interactions by competing for hydrogen bonds, depending on the solvent properties, [21] and Monte Carlo simulations are in agreement with a perturbation of the hydrogen-bond network in a confined environment. [22] Hence, one can speculate that the reduced adsorption constants observed in this work for confined pores may result from a reduced tendency for hydrogen bonding caused by a modification of the solvent properties in small pores.…”

“…One possible explanation is a reduced tendency for hydrogen bonding in mesopores because it is known that the adsorption of [Ni(en) 3 ] 2 + is more complicated than simple ion pair formation. [20] The decrease in the adsorption constant with decreasing pore size could have major consequences for controlling the transport of environmental contaminants and for the preparation of heterogeneous catalysts, and therefore, deserve further investigations. Because the alumina samples used for this study have three different crystallographic structures (h, g, d) and relatively broad pore size distributions, it would be interesting to confirm these results and to use model alumina with controlled pore sizes, such as those recently developed by grafting aluminium alkoxides on ordered silica A C H T U N G T R E N N U N G mesoporous supports.…”

Silica Surface Features and Their Role in the Adsorption of Biomolecules: Computational Modeling and Experiments

“…In a study of Ni II complexes adsorption (these are significant as precursors of supported catalysts), Boujday et al 186,187 measured adsorption isotherms for several polyamine-aqua complexes and observed well-defined and different saturation coverages, which were rationalized by postulating cooperative adsorption sites consisting in 1 to 3 silanols able to act as ligands to the metal ion, together with H-bond accepting groups in close vicinity. 29 where STM allowed for the first time to visualize in real space the (SiO) n rings that were so far only indirectly postulated, and thus to obtain experimental histograms of ring size distribution.…”

Synthesis of nickel nanoparticles supported on metal oxides using electroless plating: Controlling the dispersion and size of nickel nanoparticles

“…Tables 1 and S2 show that more decrease of pH and less activation time and plating time are observed on the metal oxide with higher IEP. Boujday et al [51][52][53] and others [4,5] have studied the adsorption of the nickel complexes, [Ni(en) 2 (H 2 O) 2 ] 2+ , at the amorphous silica/electrolyte solution interface. The EXAFS found that hydrogen bonds are formed between the -NH groups of the en and the neighboring silanol/silanolate groups or oxygen atoms of the · · ·Si-O-Si· · · siloxane linkages participating in the constrained rings of three or four SiO 4 tetrahedra.…”