Nathalie Audebrand

The Kagomé Topology of the Gallium and Indium Metal-Organic Framework Types with a MIL-68 Structure: Synthesis, XRD, Solid-State NMR Characterizations, and Hydrogen Adsorption

The vanadium-based terephthalate analogs of MIL-68 have been obtained with gallium and indium (network composition: M(OH)(O(2)C-C(6)H(4)-CO(2)), M = Ga or In) by using a solvothermal synthesis technique using N,N-dimethylformamide as a solvent (10 and 48 h, for Ga and In, respectively, at 100 degrees C). They have been characterized by X-ray diffraction analysis; vibrational spectroscopy; and solid-state (1)H and (1)H-(1)H radio-frequency-driven dipolar recoupling (RFDR), (1)H-(1)H double quantum correlation (DQ), and (13)C{(1)H} cross polarization magic angle spinning (CPMAS) NMR spectroscopy. The three-dimensional network with a Kagomé-like lattice is built up from the connection of infinite trans-connected chains of octahedral units MO(4)(OH)(2) (M = Ga or In), linked to each other through the terephthalate ligands in order to generate triangular and hexagonal one-dimensional channels. The presence of DMF molecules with strong interactions within the channels as well as their departure upon calcination (150 degrees C under a primary vacuum) of the materials has been confirmed by subjecting MIL-68 (Ga) to solid-state (1)H MAS NMR. The (1)H-(1)H RFDR and (1)H-(1)H DQ spectra revealed important information on the spatial arrangement of the guest species with respect to the hybrid organic-inorganic network. (13)C{(1)H} CPMAS NMR of activated samples provided crystallographically independent sites in agreement with X-ray diffraction structure determination. Brunauer-Emmett-Teller surface areas are 1117(24) and 746(31) m(2) g(-1) for MIL-98 (Ga) and MIL-68 (In), respectively. Hydrogen adsorption isotherms have been measured at 77 K, and the storage capacities are found to be 2.46 and 1.98 wt % under a saturated pressure of 4 MPa for MIL-68 (Ga) and MIL-68 (In), respectively. For comparison, the hydrogen uptake for the aluminum trimesate MIL-110, which has an open framework with 16 A channels, is 3 wt % under 4 MPa.

Structural and Luminescent Properties of Micro- and Nanosized Particles of Lanthanide Terephthalate Coordination Polymers

Reaction in water between rare earth ions (Ln = Y, La-Tm, except Pm) and the sodium salt of terephthalic acid leads to a family of lanthanide-based coordination polymers of general formula [Ln2(C8H4O4)3(H2O)4] n with Ln = La-Tm or Y. The isostructurality of the compounds with the previously reported Tb-containing polymer is ascertained on the basis of their X-ray powder diffraction diagrams. The coordination water molecules can be reversibly removed without destroying the crystal structure for compounds involving one of the lighter lanthanide ions (La-Eu). For compounds involving one of the heavier lanthanide ions (Tb-Tm) or yttrium, a structural change occurs during the drying process. X-ray diffraction data show this new anhydrous phase corresponding to the linking of pairs of Er(III) ions through mu-carboxylate bridges. Porosity profiles calculated for the anhydrous phases of Tb(III) and Er(III) show the presence of channels with very small sections. The luminescent properties of all the compounds have been recorded and the two most luminescent polymers, namely, the europium- and the terbium-containing ones, have been studied in more detail. Tb(III)-containing compounds display large quantum yields, up to 43%. Polyvinylpyrrolidone nanoparticles doped with [Ln2(C8H4O4)3(H2O)4] n (Ln = Eu, Tb, Er) have also been synthesized and characterized. The encapsulation of the coordination polymers results in somewhat reduced luminescence intensities and lifetime, but the nanoparticles can be dispersed in water and remain unchanged in this medium for more than 20 h.

A new ternary cadmium–zirconium–sodium oxalate with an open framework: crystal structure, solid-state NMR spectroscopy and thermal behavior

Abstract A mixed cadmium-zirconium-sodium oxalate with an open architecture has been synthesized from precipitation methods at ambient pressure. It crystallizes in an hexagonal system, space group P6422 (no. 181), a= 8.793(1) A , c= 24.530(1) A , V= 1642.5(3) A 3 and Z=3. The structure displays a [CdZr(C2O4)4]2− helicoidal framework. It is built from CdO8 and ZrO8 square-based antiprisms connected through bichelating oxalates and displays channels along different directions. The sodium counter-cations are located inside the voids of the structure together with water molecules. They exhibit a dynamic disorder which has been further investigated by 1H and 23Na solid-state NMR. The study pointed out two types of water molecules and sodium atoms, with a high mobility for one of each. The thermal decomposition has been studied in situ by temperature-dependent X-ray diffraction and thermogravimety. The final product is a mixture of cadmium oxide, zirconium oxide and amorphous sodium carbonate.

Synthesis, crystal structure and thermal behaviour of CdZrK2(C2O4)4.8H2O

The crystal structure of the new ternary oxalate CdZrK2(C2O4)4·8H2O was solved from single-crystal diffraction data. The crystal data are as follows: tetragonal symmetry, space group I (No. 82), a = 11.216(5), c = 8.954(5) A, Z = 2. The structure is built from 8-fold coordinated cadmium, zirconium and potassium atoms. It consists of zigzag chains formed by alternated CdO8 and ZrO8 polyhedra connected by bidentate oxalate groups. The chains are linked together through KO8 polyhedra. Relationships with the structure of cadmium zirconium oxalate is discussed, as well as the various structure types already known. It is shown that the crystal structures are characterised by chemically identical [CdZr(C2O4)4]2− anionic frameworks with different topologies, in which the additional cations are inserted. This structure overview suggests the possibility of conceiving new cadmium–zirconium–oxalate based materials. The thermal behaviour of the new compound is described in detail from temperature dependent X-ray powder diffraction and thermogravimetric measurements. The final decomposition product is a mixture of cadmium and zirconium oxides.

A 9,9′-spirobifluorene based Metal–Organic Framework: synthesis, structure analysis and gas sorption properties

The new square planar tetracarboxylate ligand L (4,4′,4′′,4′′′-(9,9′-spirobi[fluorene]-2,2′,7,7′-tetrayl)tetrabenzoic acid) was synthesized and used for synthesis of the Metal–Organic Framework Cu2L(H2O)2·(EtOH)4 denoted SBF–Cu. This material possesses the classical 4–4 regular tiling topology with paddle-wheel inorganic building units. Due to the presence of SBF cores, the interactions between the layers of this MOF confer it specific properties: high specific surface area, open metal sites under activation, and promising hydrogen uptake capacity.

Superstructure of a Substituted Zeolitic Imidazolate Metal–Organic Framework Determined by Combining Proton Solid‐State NMR Spectroscopy and DFT Calculations

We report the supercell crystal structure of a ZIF-8 analog substituted imidazolate metal-organic framework (SIM-1) obtained by combining solid-state nuclear magnetic resonance and powder X-ray diffraction experiments with density functional theory calculations.

Dislocation densities and crystallite size distributions in nanocrystalline ball-milled fluorides, MF2 (M = Ca, Sr, Ba and Cd), determined by X-ray diffraction line-profile analysis

The dislocation densities and crystallite size distributions in ball-milled fluorides, MF 2 (M = Ca, Sr. Ba and Cd), of the fluorite structure type have been determined as a function of milling time by X-ray diffraction line-profile analysis. The treatment has been based on the concept of dislocation contrast to explain strain anisotropy by means of the modified Williamson-Hall and Warren-Averbach approaches and a whole-profile fitting method using physically based functions. In most cases, the measured and calculated patterns are in perfect agreement; however, in some specific cases, the first few measured profiles appear to be narrower than the calculated ones. This discrepancy is interpreted as the result of an interference effect similar to that described by Rafaja, Klemm, Schreiber, Knapp & Kuzel [J. Appl. Cryst. (2004), 37, 613-620]. By taking into account and correcting for this interference effect, the microstructure of ball-milled fluorides is determined in terms of dislocation structure and size distributions of coherent domains. A weak coalescence of the crystallites is observed at longer milling periods. An incubation period in the evolution of microstrains is in correlation with the homologous temperatures of the fluorides.

Dislocations and crystallite size distribution in nanocrystalline CeO2 obtained from an ammonium cerium(IV)-nitrate solution

Abstract Nanocrystalline CeO2 powder has been obtained by thermal decomposition of hydrated ceria prepared from a solution of ammonium cerium(IV) nitrate. Thermal treatments up to 700°C were applied in order to reduce microstrains without substantial increase of grain growth. Crystallite size and size-distribution has been determined by X-ray diffraction profile analysis. The Williamson–Hall plots of the FWHM have revealed pronounced strain anisotropy which has been treated and rationalised in terms of the dislocation model of the mean square strain in the modified Williamson–Hall plots. The dislocation densities were obtained from the modified Warren–Averbach method. A strong decrease of the dislocation density and a slight increase of the crystallite size is observed with increasing annealing temperature.

Temperature-dependent X-ray diffraction and crystal structure of CeRb2(NO3)5 · 4H2O

Abstract The structure of CeIIIRb2(NO3)5 · 4H2O was determined from single crystal diffraction. The symmetry is monoclinic (space group Cc): a = 11.050(1) A , b = 8.977(1) A , c = 17.859(2) A , β = 100.877(9) °, Z = 4. The structure consists of icosahedra [Ce(NO3)5(H2O)2]2− linked by hydrogen bonds. The Rb atoms and two water molecules are located between these polyhedra and ranged in an alternating sequence along [010]. From temperature-dependent X-ray diffraction and thermogravimetry measurements, the occurrence of CeRb2(NO3)5 · 3H2O, CeRb2(NO3)5 · 2H2O, α- or β-CeRb2(NO3)5 in crystalline or amorphous forms, and the mixture of Ce2Rb3(NO3)9 and CeRb(NO3)4, have been shown during the thermal decomposition. The transformations are atmosphere and particle-size dependent, and the dehydration mechanisms are discussed.

Effect of co-existing ions during the preparation of alumina by electrolysis with aluminum soluble electrodes: Structure and defluoridation activity of electro-synthesized adsorbents

The electrochemical dissolution of aluminum was carried out to prepare hydrated aluminas which were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), chemical titrations and defluoridation activities. Aluminas were obtained at controlled pH depending upon the counter cations of the electrolyte. A boehmite AlOOH phase was isolated mainly in ammonium solution, while aluminas synthesized in the other media contained a mixture of phases, usually both boehmite and bayerite γ-Al(OH)₃. All the boehmite phases contained nano-crystallites of less than 3 nm. Batch defluoridation experiments revealed a second influence of the original electrolyte. Aluminas were very effective in defluoridation with abatement rates of 99.5%, 98.5% and 97.3% from neutral fluoride solution at 10 mgL(-1) when they were prepared in solution of (NH₄)₂SO₄, (NH₄)HCO₂ and NH₄Cl, respectively. The maximum fluoride capacities were 46.94; 10.25 and 12.18 mg g(-1) for aluminas prepared in solution of (NH₄)₂SO₄; (NH₄)HCO₂ and NH₄Cl, respectively. The amount of dissolved Al was found to be less than 0.19 mgL(-1) at neutral pH. These results show that a defluoridation with electro-synthesized aluminas would be more efficient and safe than a direct electrocoagulation.