Showing papers by "Thierry Loiseau published in 2014"

Nanoporous Solids: How Do They Form? An In Situ Approach

Abstract: Understanding the crystallization mechanisms of nanoporous solids remains one of the most challenging issues in materials science. This Short Review focuses on the use of in situ nuclear magnetic resonance (NMR) spectroscopy under hydrothermal conditions to investigate the structure, dynamics, and stability/reactivity of the soluble species present in the synthesis medium during the crystallization. We describe how the formal SBU (secondary building units) concept for solid construction can experimentally be investigated, checked, and validated on some representative purely inorganic porous phosphates as well as hybrid metal organic framework (MOF) materials. We also discuss the specific role of reactive species identified in solution to lead to intermediate or more elaborate structures such as the PNBU (prenucleation building units) or the MBU (neutral molecular building units), respectively. In certain cases, the proposed models could not to be generalized depending on the reaction conditions, the chemi...

Crystal Chemistry of Uranyl Carboxylate Coordination Networks Obtained in the Presence of Organic Amine Molecules

Abstract: Three uranyl isophthalates (1,3-bdc) and two uranyl pyromellitates (btec) of coordination-polymer type were hydrothermally synthesized (200 °C for 24 h) in the presence of different amine-based molecules [1,3-diaminopropane (dap) or dimethylamine (dma) originating from the in situ decomposition of N,N-dimethylformamide]. (UO2)2(OH)2(H2O)(1,3-bdc)·H2O (1) is composed of inorganic tetranuclear cores, which are linked to each other through the isophthalato ligand to generate infinite neutral ribbons, which are intercalated by free H2O molecules. The compounds (UO2)1.5(H2O)(1,3-bdc)2·0.5H2dap·1.5H2O (2) and UO2(1,3-bdc)1.5·0.5H2dap·2H2O (3) consist of discrete uranyl-centered hexagonal bipyramids connected to each other by a ditopic linker to form a single-layer network for 2 or a double-layer network for 3. The protonated diamine molecules are located between the uranyl–organic sheets and balance the negative charge of the layered sub-networks. The phase (UO2)2O(btec)·2Hdma·H2O (4) presents a 2D structure built up from tetranuclear units, which consist of two central sevenfold coordinated uranium centers and two peripheral eightfold coordinated uranium centers. The connection of the resulting tetramers through the pyromellitate molecules generates an anionic layerlike structure, in which the protonated dimethylammonium species are inserted. The compound UO2(btec)·2Hdma (5) is also a lamellar coordination polymer, which contains isolated eightfold coordinated uranium cations linked through pyromellitate molecules and intercalated by protonated dimethylammonium species. In both phases 4 and 5, the btec linker has non-bonded carboxyl oxygen atoms, which preferentially interact with the protonated amine molecules through a hydrogen-bond network. The different illustrations show the structural diversity of uranyl–organic coordination polymers with organic amine molecules as countercations.

The Crystal Chemistry of Uranium Carboxylates

Abstract: The field of uranium carboxylates has been studied for several decades and an important library of coordination complexes and network solids is now well defined. It mainly concerns the reactivity of hexavalent uranium (uranyl) with the different types of carboxylic acids containing monodentate or polydentate functions, aliphatic or aromatic carbon backbone, or hetero-systems offering other functionalities (N-donor, S-donor, phosphonates, …). A rich variety of molecular complexes or extended multi-dimensional networks (1D, 2D, 3D) has been identified and depends mainly on the equatorial connectivity of the uranyl cation (UO22+) in different coordination numbers (tetragonal, pentagonal or hexagonal bipyramid). The yl oxo groups remain relatively inert to condensation process (except rare case of cation–cation interaction). For lower oxidation state of uranium (+3, +4, +5), the knowledge is at the infancy stage since very few contributions are available in literature. Nevertheless, recent contributions have shown the possibilities of the reactivity of tetravalent uranium in relatively stable architectures, either at the molecular level, with high nuclearities (up to U38), or engaged in three-dimensional frameworks. The scope of this review is a comprehensive presentation of the crystal structures resulting from the different types of complexation of uranium with carboxylic acid molecules (excepting oxalate ligand) and their classification as a function of the nuclearity of identified building units.

Nanoporous Solids: How Do They Form? An in situ Approach

Abstract: Review: focus on in situ NMR spectroscopy of the soluble species present in syntheses media during crystallization; 81 refs.

Isolation of the Large {Actinide}38 Poly-oxo Cluster with Uranium.

Abstract: Black crystals of U38O56Cl18(thf)8 (BzO)24·8THF are solvothermally synthesized from a mixture of UCl4, Bz-OH, THF, and a controlled amount of H2O (autoclave, Ar, 130 °C, 36 h, 72% yield).

Crystal Structures of Tetravalent Uranium Fluorides Obtained in the Presence of Hydrazine from Uranyl Source.

Abstract: The crystal structures of the tetravalent uranium fluorides (V), (VI), (IX), and (X), which could not be prepared as single phases, are determined by single crystal XRD.

Production method for metal-organic structure-type crystalline porous aluminum aromatic azo-carboxylate

Abstract: PROBLEM TO BE SOLVED: To provide a production method for a metal-organic structure (MOF) solid of porous crystal aluminum aromatic azo-carboxylate used as liquid or gas molecule storage, selective gas separation and catalyst.SOLUTION: A method for producing a crystalline porous aluminum aromatic azo-carboxylate MOF solid represented in Figure 5, comprises the steps of: (i) mixing a metal-inorganic precursor represented by metal salt Al3+, and an organic precursor of ligand represented by azobenzene-4,4'-dicarboxylic acid, in a non-aqueous organic solvent represented by N,N-dimethyl formamide; and (ii) heating the mixture at temperature of at least 50°C to obtain a solid.