Showing papers by "Thierry Loiseau published in 2015"

Thorium terephthalates coordination polymers synthesized in solvothermal DMF/H2O system.

Abstract: A series of thorium-based terephthalates have been solvothermaly synthesized in N,N-dimethylformamide (DMF) with different amounts of water and various temperatures (100–150 °C). Without the addition of water, the Th–H2bdc–DMF system gives rise to the formation of two phases, Th(bdc)2(DMF)2 (1) and Th6O4(OH)4(H2O)6(bdc)6·6DMF·12H2O (3) (bdc = 1,4-benzenedicarboxylate or terephthalate). Their structures are built up of isolated thorium centers ThO8(DMF)2 for (1) and the hexanuclear core Th6O4(OH)4(H2O)6 for (3). The latter adopts the UiO-66 metal–organic framework topology and exhibits a very high porosity for an actinides-based porous material (BET surface up to 730(6) m2·g–1). The synthesis of (3) is also favored upon adding water. However, for pure aqueous solutions or for a very low amount of water, a third solid Th(bdc)2 (2) crystallizes and contains thorium monomers ThO8. The main similitude with the parent system dedicated to tetravalent uranium concerns the possibility to stabilize the An6O8(H2O)6 ...

The direct heat measurement of mechanical energy storage metal-organic frameworks.

Abstract: In any process, the heat exchanged is an essential property required in its development. Whilst the work related to structural transitions of some flexible metal-organic frameworks (MOFs) has been quantified and linked with potential applications such as molecular springs or shock absorbers, the heat related to such transitions has never been directly measured. This has now been carried out with MIL-53(Al) using specifically devised calorimetry experiments. We project the importance of these heats in devices such as molecular springs or dampers. Language: en

Coordination polymers of uranium(IV) terephthalates

Abstract: A series of tetravalent uranium terephthalates has been solvothermally synthesized in the solvent N,N-dimethylformamide (DMF) at temperature 100–150 °C with different water amounts. Composition diagrams have been determined for the U4+ metallic cation in the presence of terephthalic acid, and their crystal structures revealed the occurrence of two- or three-dimensional coordination polymers. In the absence of water, a mixture of two polytypes T-U2Cl2(bdc)3(DMF)4 (1) and M-U2Cl2(bdc)3(DMF)4 (2) has been identified at low temperature (100–110 °C) for bdc/U = 1–4 (bdc = terephthalate linker). Their structures are built up from isolated uranium centers in nine-fold coordination, surrounded by 6 carboxyl oxygen atoms, 2 oxygen atoms coming from DMF molecules and one chlorine atom. The uranium cations are linked to each other through the bdc ligand in order to generate a 3D framework. By increasing the temperature (130–150 °C), a layered like compound has been isolated, U2(bdc)4(DMF)4 (3). It is composed of discrete actinide centers in ten-fold coordination, with 8 carboxyl oxygen atoms and 2 oxygen atoms from DMF molecules. The connection of the UO10 units with the bdc linkers generates 2D sheets. When a controlled amount of water is added to the reaction medium, the crystallization of the UiO-66-like U6O4(OH)4(H2O)6(bdc)6·10DMF solid (containing a hexanuclear sub-unit) is observed for temperature 110–120 °C and the H2O/U molar ratio in the range of 2–10. At higher temperature (140–150 °C), a distinct phase appeared, U2O2(bdc)2(DMF) (4), which consists of infinite chains of uranium centers, linked to each other via the bdc ligands. Higher water contents led to the formation of urania UO2.

Stabilization of Tetravalent 4f (Ce), 5d (Hf), or 5f (Th, U) Clusters by the [α-SiW9O34](10-) Polyoxometalate.

Abstract: The reaction of Na10[α-SiW9O34] with tetravalent metallic cations such as 4f ((NH4)2Ce(NO3)6), 5d (HfCl4), or 5f (UCl4 and Th(NO3)4) in a pH 4.7 sodium acetate buffer solution leads to the formation of four sandwich-type polyoxometalates [Ce4(μ(3)-O)2(SiW9O34)2(CH3COO)2](10-) (1), [U4(μ(3)-O)2(SiW9O34)2(CH3COO)2](10-) (2), [Th3(μ(3)-O)(μ(2)-OH)3(SiW9O34)2](13-) (3), and [Hf3(μ(2)-OH)3(SiW9O34)2](11-) (4). All four compounds consist of a polynuclear cluster fragment stabilized by two [α-SiW9O34](10-) polyanions. Compounds 1 and 2 are isostructural with a tetranuclear core (Ce4, U4), while compound 3 presents a trinuclear Th3 core bearing a μ(3)-O-centered bridge. It is an unprecedented configuration in the case of the thorium(IV) cluster. Compound 4 also possesses a trinuclear Hf3 core but with the absence of the μ(3)-O bridge. The molecules have been characterized by single-crystal X-ray diffraction, (183)W and (29)Si nuclear magnetic resonance (NMR) spectroscopy, infrared (IR) spectroscopy, thermogravimetric analysis (TGA), and scanning electron microscopy/energy-dispersive X-ray (SEM/EDX) analysis.

Ex-Situ Kinetic Investigations of the Formation of the Poly-Oxo Cluster U38

Abstract: The ex-situ qualitative study of the kinetic formation of the poly-oxo cluster U38 , has been investigated after the solvothermal reaction The resulting products have been characterized by means of powder XRD and scanning electron microscopy (SEM) for the solid phase and UV/Vis, X-ray absorption near edge structure (XANES), extended X-ray absorption fine structure (EXAFS), and NMR spectroscopies for the supernatant liquid phase The analysis of the different synthesis batches, stopped at different reaction times, revealed the formation of spherical crystallites of UO2 from t=3 h, after the formation of unknown solid phases at an early stage The crystallization of U38 occurred from t=4 h at the expense of UO2 , and is completed after t=8 h Starting from pure uranium(IV) species in solution (t=0-1 h), oxidation reactions are observed with a U(IV) /U(VI) ratio of 70:30 for t=1-3 h Then, the ratio is inversed with a U(IV) /U(VI) ratio of 25/75, when the precipitation of UO2 occurs Thorough SEM observations of the U38 crystallites showed that the UO2 aggregates are embedded within This may indicate that UO2 acts as reservoir of uranium(IV), for the formation of U38 , stabilized by benzoate and THF ligands During the early stages of the U38 crystallization, a transient crystallized phase appeared at t=4 h Its crystal structure revealed a new dodecanuclear moiety (U12 ), based on the inner hexanuclear core of {U6 O8 } type, decorated by three additional pairs of dinuclear U2 units The U12 motif is stabilized by benzoate, oxalates, and glycolate ligands

B-α-[AsW9O33]9− polyoxometalates incorporating hexanuclear uranium {U6O8}-like clusters bearing the UIV form or unprecedented mixed valence UIV/UVI involving direct UVIO–UIV bonding

Abstract: The use of B-α-[AsW9O33]9− anionic moieties in association with the tetravalent 5f uranium UCl4 precursor affords three new hexanuclear uranium {U6O8}-like clusters embedded in a polyoxometalate architecture. Two of them are constituted by an unprecedented uranium mixed valence UIV/UVI cluster.

Solvothermal Synthesis of Tetravalent Uranium with Isophthalate or Pyromellitate Ligands

Abstract: Three new coordination polymers bearing tetravalent uranium have been isolated with the O-donor ligands such as isophthalate (1,3-bdc) or pyromellitate (btec). The compounds 1 and 3 have been solvothermaly synthesized in N,N-dimethylformamide (DMF). The crystal structure of U(1,3-bdc)2(DMF) (1) is built up from discrete tricapped trigonal-primastic UO9 units, for which one carbonyl oxygen atom from DMF is bound to uranium. The connection of the UO9 units with the isophthalate linkers occurs in a chelating and bidentate fashion and gives rise to the formation of a 3D framework, delimiting narrow channels running along the [101] direction. Upon heating, the DMF molecules are removed, generating the second phase U(1,3-bdc)2 (2) compound, closely related to 1. Indeed, the coordination environment of uranium is reduced to eight with a distorted square-antiprismatic geometry. This transition induces the relative shrinkage of the network (ΔV = 23 %). The structure of the compound U(btec)(DMF)2 (3) also exhibits a 3D framework composed of an isolated bicapped square-antiprismatic UO10 unit, for which two carbonyl oxygen atoms from DMF are bonded to uranium. Pyromellitate ensures the connection of the UO10 units through the carboxylate arms in a chelating mode. This results in the formation of a network with diamond-shaped channels, developed along the c axis and encapsulating the DMF molecules. In contrast to 1, no stable phase is observed upon removing the DMF species by heating.

Synthesis of zirconium oxycarbide powders using metal–organic framework (MOF) compounds as precursors

Abstract: ZrCxOy oxycarbides were synthesized for the first time by using metal–organic framework (MOF) compounds as precursors. These MOFs, based on zirconium carboxylates, are derived from the UiO-66 type structure. Three different Zr-MOF compounds were synthesized, differing by their C/Zr ratio, due to the use of terephthalic acid (C/Zr = 8, or UiO-66), naphthalene-2,6-dicarboxylic acid (C/Zr = 12) and biphenyl-4,4′-dicarboxylic acid (C/Zr = 14 or UiO-67). The oxycarbide crystallites obtained through appropriate thermal treatments (under Ar atmosphere) of the Zr-MOF precursors show an average size of a few hundred microns. They are surrounded by an outer rim of turbostratic carbon, whose thickness is directly relevant to the C/Zr ratio coming from the nature of the organic linker. The composition of the oxycarbides obtained was estimated on the basis of the cell parameters refined from the powder XRD patterns. The oxycarbides synthesized from naphtalene-2,6-dicarboxylic acid and biphenyl-4,4′-dicarboxylic acid are close to ZrC0.925O0.075, while that of the oxycarbide obtained from the terephthalic acid precursor is ZrC0.944O0.056. It results that the carbon richer oxycarbide product is observed for the UiO-66 precursor synthesized with terephthalic acid, and exhibiting the lower C/Zr ratio of the series. The composition of the oxycarbide powders is shown to be directly relevant to the mechanisms of decomposition of the Zr-MOF compound involved during heating.

Luminescent Lanthanide Metal Organic Frameworks for cis-Selective Isoprene Polymerization Catalysis

Abstract: In this study, we are combining two areas of chemistry; solid-state coordination polymers (or Metal-Organic Framework—MOF) and polymerization catalysis. MOF compounds combining two sets of different lanthanide elements (Nd3+, Eu3+/Tb3+) were used for that purpose: the use of neodymium was required due to its well-known catalytic properties in dienes polymerization. A second lanthanide, europium or terbium, was included in the MOF structure with the aim to provide luminescent properties. Several lanthanides-based MOF meeting these criteria were prepared according to different approaches, and they were further used as catalysts for the polymerization of isoprene. Stereoregular cis-polyisoprene was received, which in some cases exhibited luminescent properties in the UV-visible range.

Stabilization of Tetravalent 4f (Ce), 5d (Hf), or 5f (Th, U) Clusters by the [α‐SiW9O34]10‐ Polyoxometalate.

Abstract: The crystal structures of compounds (IV), (VII), (X), and (XIII) are determined by single crystal XRD.