From molecular chemistry to hybrid nanomaterials. Design and functionalization.

This tutorial review reports upon the organisation and functionalization of two families of hybrid organic-inorganic materials. We attempted to show in both cases the best ways permitting the organisation of materials in terms of properties at the nanometric scale. The first family concerns mesoporous hybrid organic-inorganic materials prepared in the presence of a structure-directing agent. We describe the functionalization of the channel pores of ordered mesoporous silica, that of the silica framework, as well as the functionalization of both of them simultaneously. This family is currently one of the best supports for exploring polyfunctional materials, which can provide a route to interactive materials. The second family concerns lamellar hybrid organic-inorganic materials which is a new class of nanostructured materials. These materials were first obtained by self-assembly, as a result of van der Waals interactions of bridged organosilica precursors containing long alkylene chains during the sol-gel process, without any structure directing agent. This methodology has been extended to functional materials. It is also shown that such materials can be obtained from monosilylated precursors.

Self-assembly of layered organosilicas based on weak intermolecular interactions.

New layered hybrid organic-inorganic materials were obtained directly by hydrolysis and polycondensation of monosilylated precursors of type (EtO)(3)Si(CH(2))(3)NH(C=O)NHC(n)H(2n+1) (n = 3, 8, 12 and 16). These precursors were easily prepared by reaction between commercially available triethoxysilylpropylisocyanate and primary aminoalkanes. The obtained materials were characterized by combining elemental analysis, X-ray powder diffraction, (13)C, (29)Si NMR and FT-IR spectroscopies. They were found to be well condensed, and stable in water. We showed that their formation results from a cooperative effect between hydrogen bonding interactions originating from ureido groups and hydrophobic interactions between the long alkyl chains. There is no formation of material when n = 2, or from (EtO)(3)SiC(n)H(2n+1) when n = 18, thus proving that both types of weak intermolecular interactions are required. The chelating property of these materials towards europium(III) ions was tested.

Selective lanthanides sequestration based on a self-assembled organosilica.

In this paper, we investigate the cation-exchange properties of a self-assembled hybrid material towards trivalent ions, lanthanides (La(3+), Eu(3+), Gd(3+), Yb(3+)) and Fe(3+). The bis-zwitterionic lamellar material was prepared by sol-gel process from only 3-aminopropyltriethoxysilane (APTES), succinic anhydride, and ethylenediamine. In ethanol heated under reflux, the exchange ethylenediammonium versus Ln(3+) proved to be complete by complexometry measurements and elemental analyses, one Cl(-) ion per one Ln(III) remaining as expected for charge balance. In aqueous solution at 20 degrees C, the material was found to be selective towards lanthanide in spite of the similarity of their ionic radii. The cation uptake depends on the nature of the salt, the difference between two lanthanides reaching up to 20 % in some cases. Finally, ion-exchange reaction with FeCl(3) was chosen as a probe to get more information on the material after incorporation of trivalent ions. Based on Mössbauer spectroscopic investigations on the resulting material in conjunction with the XRD analysis of materials containing trivalent ions, a structural model was proposed to describe the incorporation of trivalent ions by exchange reaction within the original zwitterionic material.

Mesoporous materials with an acidic framework and basic pores. A successful cohabitation.

Bifunctional mesoporous material with an acidic framework and basic pores was synthesized via the co-condensation of TEOS, bistrimethoxysilylated precursors with a disulfide core, and 3-tert-butyloxycarbonyl (aminopropyl)triethoxysilane using P123 as surfactant; the reduction of disulfide units to SH groups followed by their oxidation into SO3H and deprotection of amino groups gave rise to a material containing two antagonist functionalities located at the nanometric scale in a successful cohabitation, avoiding their mutual destruction in the presence of aprotic solvent. This kind of material illustrates the large possibilities offered by mesoporous materials and opens new and unsuspected applications.

First direct synthesis of highly ordered bifunctionalized mesoporous silica thin films.

Optically transparent and highly ordered mesoporous organosilica thin films functionalized with two different organic groups in various proportions were synthesized by templated-directed cocondensation of tetraethylorthosilicate (TEOS) and a mixture of two distinct and functional organotriethoxysilanes [NC(CH2)3Si(OEt)3 and O=P(OEt)2(CH2)3Si(OEt)3]. The mesostructured films obtained by evaporation induced self-assembly (EISA) approach were deposited on glass or silicon substrates by dip-coating. They were characterized by Grazing Incidence Small Angle X-ray Scattering (GISAXS) and X-ray reflectivity. We showed that whatever the proportion in organic groups, only 2D hexagonal phase having p6m symmetry was observed for all the materials indicating a good compatibility between the organic groups. The bi-functionalization of the internal pores surface by the organotriethoxysilanes groups was clearly evidenced by using micro-Raman spectroscopy.

An original synthesis of highly ordered organosilica with a high content of thiol groups.

Well ordered bridged organosilica highly functionalised with disulfide groups were obtained by self-assembly of alpha,omega-bis(trimethoxysilyl)alkyldisulfide under hydrophilic conditions; the reduction of disulfide cores to SH groups gave rise to material having a high mercury ion adsorption capacity.

CO2 as a supramolecular assembly agent: a route for lamellar materials with a high content of amine groups.

The uptake of carbon dioxide on N-(2-aminoethyl)-3-aminopropyltrimethoxysilane 1 and N-(6-aminohexyl)-3-aminopropyltrimethoxysilane 2 afforded a supramolecular network of bis-silylated ammonium carbamate salts, the hydrolytic polycondensation of which gave rise to structured hybrid materials. Subsequent loss of CO2 was readily achieved upon heating, thus generating materials in which the structure was maintained (well-defined lamellar structure from 2) and contains free amino groups. The accessibility of amine-functionalized groups was shown by their ability to complex transition metal or lanthanide salts.

One-step template-directed synthesis of multifunctionalised nanoporous silica: on the way to interactive nanomaterials.

The preparation of multifunctional mesoporous silica containing a NLO chromophore in the framework (bridged azobenzene phosphonium salts) and mercaptopropyl groups able to stabilize gold(0) nanoparticles in the channel pores was achieved in one step by using the direct liquid crystal templating approach.

Direct syntheses of functionalized mesostructured silica by using an inexpensive silica source.

The co-condensation of water soluble sodium silicate and different organotrialkoxysilanes in the presence of non-ionic triblock copolymers under acidic conditions provides a very convenient, general and economic one step synthesis methodology for the preparation of organically functionalised mesostructured silica.

Coordination chemistry in the solid: evidence for coordination modes within hybrid materials different from those in solution.

Two routes of incorporation of europium(III) salts into cyclam-containing hybrid materials have been explored, to elucidate the coordination mode of EuIII in cyclam-containing hybrid materials in a study of the arrangement of cyclam moieties during the solgel process. They were 1) complexation of europium salts by N-tetrasubstituted 1,4,8,11-tetraazacyclotetradecane (cyclam) derivatives bearing four hydrolysable Si(OEt)3 groups, followed by hydrolysis and polycondensation of these complexes; and 2) hydrolysis and polycondensation of N-tetrasubstituted silylated cyclam derivatives, then incorporation of europium salts directly into the hybrid materials. The coordination mode of europium salts within solids is not the same as in solution. In solution, the complexation of EuIII with cyclam is not possible; it requires cyclam derivatives containing N-chelating substituents such as amido groups in an appropriate geometry. In contrast, the incorporation of EuIII into hybrid materials is always possible, whatever the nature of the arms of the cyclam moieties. Thus, EuIII uptake is one EuIII/two macrocycles with cyclam moieties containing N-alkyl substituents. This constitutes the first example of 4N + 4N lanthanide coordination.

Evidence for Nondissociative Ligand Exchange within [4+2]-Coordinate Phosphorus Species in Solution.

[4+2]-Coordinate phosphorus compounds, [bis(8-(dimethylamino)-1-naphthyl)]phenylphosphane, [bis(8-(dimethylamino)-1-naphthyl)]phenylphosphane sulfide, [bis(8-(dimethylamino)-1-naphthyl)]phenylphosphonium bromide, [bis(8-(dimethylamino)-1-naphthyl)]methylphosphane, and [bis(8-(dimethylamino)-1-naphthyl)]phosphane oxide, with two identical bidentate (8-(dimethylamino)-1-naphthyl) ligands have asymmetrical geometries in solution and undergo intramolecular nondissociative ligand exchange as shown by dynamic (1)H NMR studies. The DeltaG() values for this process were found to lie in the range 56.2-61.7 kJ mol(-)(1). The (1)H NMR study for bis[(8-(dimethylamino)-1-naphthyl)]phenylphosphane sulfide has revealed that two hexacoordinate isomers coexist in solution in a solvent dependent ratio. Their interconversion in solution is consistent with an intramolecular 1,2-shift of adjacent ligands.