No abstract

This work describes the use of mesoporous SBA-15 silicas as hard templates for the size-controlled synthesis of oxide nanoparticles, with the pores acting as nanoscale reactors. This fundamental work is mainly aimed at understanding unresolved issues concerning the occurrence and size dependence of phase transitions in oxide nanocrystals. Aqueous solutions of Fe(NO3)3*9H2O are deposited inside the pores of SBA-15 silicas with mesopore diameters of 4.3, 6.6, and 9.5 nm. By calcination, the nitrate salt transforms into FeOx oxides. The XRD peaks of nanocrystals are broad and overlapping, resulting in ambiguities attributed to a given allotropic variety of Fe2O3 (alpha, epsilon, or gamma) or Fe3O4. The association of XRD, SAED, and Raman information is necessary to solve these ambiguities. The metastable gamma-Fe2O3 variety is selectively formed at low Fe/Si atomic ratio (ca. 0.20) and when a low calcination temperature is used (773 or 873 K followed by quenching to room temperature once the targeted temperature is reached). The small size dispersion of the patterned nanoparticles, suggested on a local scale by TEM, is confirmed statistically by magnetic measurements. The nanoparticles have a superparamagnetic behavior around room temperature. Their magnetic moments (from 220 to 370 mB), their sizes (from 4.0 to 4.8 nm), and their blocking temperatures (from 36 to 58 K) increase with the silica template mesopore diameter. Their magnetic properties are compared to those of standard gamma-Fe2O3 nanoparticles of similar size, obtained by coprecipitation in water and stabilized by a citrate coating.

Ordered mesoporous silica monoliths were used as a versatile platform to study the effect of size reduction on the photomagnetic properties of the Rb 2 Co 4 [Fe(CN) 6 ] 3.3 ·nH 2 O Prussian blue derivative. Through the variation of the organization of the pores, the metal loading and the chemical composition of the solid matrix, it was possible to modify independently the aggregation state, the dilution and the chemical environment of the nanoparticles and to disentangle the effect of each parameter on the physical properties. The approach was first assessed by using the versatile platform to study the effect of [a] 1307 Figure 6. Temperature dependence of the normalized T af-be products for Hex_1_CoFeRb (filled diamonds) and Hex_0.1_CoFeRb (open diamonds).

331 977 5773. Single-crystal X-ray structure analyses for [PmimSO 3 H][PTS]: Details of the crystal data, data collection and refinement are given in Table S1. The diffraction intensities were collected with graphite-monochromatized Mo Kα radiation. Data collection and cell refinement were carried out using a Bruker Kappa X8 APEX II diffractometer. The temperature of the crystal was maintained at the selected value (200K) by means of a 700 series Cryostream cooling device to within an accuracy of ±2 K. Intensity data were corrected for Lorenz-polarization and absorption factors. The structures were solved by direct methods using SHELXS-97 1 and refined against F 2 by full-matrix least-squares methods using SHELXL-97 2 with anisotropic displacement parameters for all non-hydrogen atoms.All calculations were performed by using the Crystal Structure crystallographic software package WINGX. 3 The structure was drawn using ORTEP3. 4 All hydrogen atoms were located on a differenceFourier map and introduced into the calculations as a riding model with isotropic thermal parameters.

Synthesis of new heterometallic layered magnets with controlled chirality have been achieved by insertion of chiral and non-chiral salen-type Ni(II) complexes into copper and cobalt layered simple hydroxides.

Mesoporous silica monoliths with various ordered nanostructures containing transition metal M(2+) cations in variable amounts were elaborated and studied. A phase diagram depicting the different phases as a function of the M(2+) salt/tetramethyl orthosilicate (TMOS) and surfactant P123/TMOS ratios was established. Thermal treatment resulted in mesoporous monoliths containing isolated, accessible M(2+) species or condensed metal oxides, hydroxides, and salts, depending on the strength of the interactions between the metal species and the ethylene oxide units of P123. The ordered mesoporosity of the monoliths containing accessible M(2+) ions was used as a nanoreactor for the elaboration of various transition metal compounds (Prussian blue analogues, Hofmann compounds, metal-organic frameworks), and this opens the way to the elaboration of a large range of nanoparticles of multifunctional materials.

Four uranyl-bearing coordination polymers (1-4) have been hydrothermally synthesized in the presence of the zwitterionic 1,3-bis(carboxymethyl)imidazolium (= imdc) anion as organic linkers after reaction at 150 °C. At low pH (0.8-3.1), the form 1 ((UO2)2(imdc)2(ox)·3H2O; ox stands for oxalate group) has been identified. Its crystal structure (XRD analysis) consists of the 8-fold-coordinated uranyl centers linked to each other through the imdc ligand together with oxalate species coming from the partial decomposition of the imdc molecule. The resulting structure is based on one-dimensional infinite ribbons intercalated by free water molecules. By adding NaOH solution, a second form 2 is observed for pH 1.9-3.9 but in a mixture with phase 1. The pure phase of 2 is obtained after a hydrothermal treatment at 120 °C. It corresponds to a double-layered network (UO2(imdc)2) composed of 7-fold-coordinated uranyl cations linked via the imdc ligands. In the same pH range, a third phase ((UO2)3O2(H2O)(imdc)·H2O, 3) is formed: it is composed of hexanuclear units of 7-fold- and 8-fold-coordinated uranyl cations, connected via the imdc molecules in a layered assembly. At higher pH, the chain-like solid (UO2)3O(OH)3(imdc)·2H2O (4) is observed and composed of the infinite edge-sharing uranyl-centered pentagonal bipyramidal polyhedra. As a function of pH, uranyl nuclearity increases from discrete 8- or 7-fold uranyl centers (1, 2) to hexanuclear bricks (3) and then infinite chains in 4 (built up from the hexameric fragments found in 3). This observation emphasized the influence of the hydrolysis reaction occurring between uranyl centers. The compounds have been further characterized by thermogravimetric analysis, infrared, and luminescence spectroscopy.

A new method of acidification and subsequent functionalization of the Aurivillius-phase Bi2SrTa2O9 (BST), using microwave irradiation, was developed. This method enables to obtain hybridized phases from layered BST. Functionalization of BST by various kinds of amines and diamines can be achieved in a few hours only, compared to much longer time (over a week) using conventional heating. Good crystallinity of the compounds is kept. In addition, a microwave-assisted preintercalation strategy was developed, allowing inserting new amines (bearing cyclic or aromatic groups) between the oxide layers previously unseen in this type of compound. This work opens new perspectives for the fast and easy functionalization of layered oxides with more elaborated molecules.