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A series of Ni(II) complexes containing polyamines and 1, 2, or 3 labile aqua ligands ([Ni(en)(dien)(H2O)]²⁺, [Ni(en)2(H2O)2]²⁺, [Ni(dien)(H2O)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.

²⁷Al 3QMAS 2D NMR was used to study the molecular-level organization of a clay pillared with the “Al13(heidi)6³⁺” polycation, whose unusual structure is stabilized by hydroxyethyliminodiacetate (heidi) ligands. The quadrupolar line shape and the isotropic chemical shifts were first unambiguously determined on a solid salt of the polycation. This compound was then used to identify the fingerprint of the Al13(heidi)x³⁺ polycation in a sample of saponite clay that had been intercalated with a solution containing Al(III) and heidi ligands, showing that the basic structure of the Al polymer had been preserved upon intercalation. A more detailed analysis of 3QMAS 2D NMR line shapes indicated, however, that a selective partial hydrolysis reaction had occurred, most probably leading to Al13(heidi)3³⁺ polycations (loss of three heidi ligands). Thus, 3QMAS NMR allowed to choose one structural model for these nanocomposites from the several compatible with previously published characterizations.

It is shown that, during the preparation of Cu/SiO2 samples by selective adsorption of copper tetraammine complex [Cu(NH3)4(H2O)2]²⁺ on silica, two types of supported Cu^II species form:  grafted Cu^II ions and copper phyllosilicate. The formation of grafted Cu^II ions results from electrostatic adsorption of Cu^II ammine complex cations in solution onto the surface of silica particles negatively charged due to the high solution pH. Grafting of Cu^II ions occurs during the subsequent drying step. The formation of copper phyllosilicate takes place in solution. It results from a reaction between silicic acid arising from silica dissolution and [Cu(OH)2(H2O)4]⁰ complex in solution. Both Cu^II species lead to small metal particles after reduction. Several preparation parameters were investigated in this paper:  the metal precursor concentration, the pH of the precursor solution, the solution/silica contact time, and the addition of ammonium nitrate to the precursor solution. The amount of copper phyllosilicate depends on the pH of the precursor solution; it is maximum at pH 9, that is, at the pH at which the concentration of [Cu(OH)2(H2O)4]⁰ complex is maximum according to calculation of Cu^II speciation. The amount of copper phyllosilicate increases with the solution/silica contact time because its formation is a kinetically limited process. It was found that the addition of ammonium nitrate to the precursor solution prevents the formation of copper phyllosilicate. This can be explained by calculations of the Cu^II speciation in solution. The formation of Cu^II ammine complexes is favored in the presence of NH4⁺ so that the concentration of [Cu(OH)2(H2O)4]⁰ complex strongly decreases and its maximum of concentration shifts to pH lower than the pH’s of preparation.

The selectivity of an Al13-pillared saponite and an Al13-pillared montmorillonite for Cd²⁺ and Cu²⁺ adsorption was studied. The quantity of metal adsorbed on both pillared clays depends on the pH of the solution and the pillars density. Adsorption equilibria are regulated by the protonation equilibria of the amphoteric sites on the pillars. Pillared clays adsorb more cadmium and copper than classic aluminum hydroxides which is simply attributable to a higher density of surface aluminum groups. Significant differences in behavior are observed between pillared montmorillonite and pillared saponite. Pillared montmorillonite appears to be more acidic, which is correlated with a more advanced degree of structural modification of the pillars on calcination. We propose a tentative, partial structural model of pillar transformation compatible with these differences. At the same time, both pillared clays have similar affinities for cadmium II at low pH (5−6), but pillared montmorillonite seems to be a more efficient cadmium trap at pH = 8 when its surface groups are negatively ionized. Thus, the nature of the clay layers conditions the structural modifications of the intercalated [Al13] polycations, which in turn determine adsorptive behavior.

The microporosity of Al13-intercalated and -pillared synthetic saponites with variable layer charge (from 0.8 to 1.5 per unit cell) was studied by high-resolution quasi-equilibrium adsorption volumetry and low-temperature adsorption microcalorimetry. A strong positive correlation was observed between the adsorbed amounts of nitrogen and argon and the quantity of intercalated aluminum, suggesting that a simple micropore-filling mechanism is inappropriate to interpret N2 and Ar adsorption on intercalated and pillared clays. Adsorption energy distributions were calculated using the derivative isotherm summation (DIS) procedure. They reveal that, at 77 K, nitrogen (and argon to a lesser extent) “titrates” the Brønsted acidic sites of the pillars and does not provide direct information about the liquid microporous volume between pillars. This picture of N2 and Ar adsorption suggests a critical reexamination of many published data concerning the surface area and porous volume of pillared clays.

Model supported nickel catalysts were prepared by deposition of the [Ni(en)2(H2O)2]²⁺ complex from aqueous solutions onto silica, zeolite Y, two kinds of alumina, a clay, and a pillared clay. UV−visible spectroscopy was used to monitor the d−d transitions of Ni(II) in the solution, upon contact with the support oxide, and upon drying. In comparison with the spectra of reference compounds, and with the help of data provided by other techniques (elemental analysis, thermogravimetry, IR spectroscopy), this allowed us to follow the reactions occurring in the coordination sphere of the nickel ion during the initial stages of catalyst preparation. For the alumina, zeolite, silica, and pillared clay supports, exchange of two (H2O) ligands for support surface groups was evidenced (nickel grafting). On the other hand, deposition/intercalation into clay caused the formation of square-planar [Ni(en)2]²⁺upon drying. Therefore, these systems allow a precise study of transition metal interfacial coordination chemistry, with implications for catalyst preparation, inorganic chemistry, and colloid chemistry.