MIL-96, a Porous Aluminum Trimesate 3D Structure Constructed from a Hexagonal Network of 18-Membered Rings and μ 3 -Oxo-Centered Trinuclear Units

Institut Lavoisier (UMR CNRS 8180), Institut Universitaire de France, Porous Solids Group, Tectospin, Université de Versailles Saint Quentin en Yvelines, 45, avenue des Etats-Unis, 78035 Versailles, France.
Journal of the American Chemical Society (Impact Factor: 12.11). 09/2006; 128(31):10223-30. DOI: 10.1021/ja0621086
Source: PubMed


A new aluminum trimesate Al12O(OH)18(H2O)3(Al2(OH)4)[btc]6.24H2O, denominated MIL-96, was synthesized under mild hydrothermal conditions (210 degrees C, 24 h) in the presence of 1,3,5-benzenetricarboxylic acid (trimesic acid or H3btc) in water. Hexagonal crystals, allowing a single-crystal XRD analysis, are grown from a mixture of trimethyl 1,3,5-benzenetricarboxylate (Me3btc), HF, and TEOS. The MIL-96 structure exhibits a three-dimensional (3D) framework containing isolated trinuclear mu3-oxo-bridged aluminum clusters and infinite chains of AlO4(OH)2 and AlO2(OH)4 octahedra forming a honeycomb lattice based on 18-membered rings. The two types of aluminum groups are connected to each other through the trimesate species, which induce corrugated chains of aluminum octahedra, linked via mu2-hydroxo bonds with the specific -cis-cis-trans- sequence. The 3D framework of MIL-96 reveals three types of cages. Two of them, centered at the special positions 0 0 0 and 2/3 1/3 1/4, have estimated pore volumes of 417 and 635 A3, respectively, and encapsulate free water molecules. The third one has a smaller pore volume and contains disordered aluminum octahedral species (Al(OH)6). The solid-state NMR characterization is consistent with crystal structure and elemental and thermal analyses. The four aluminum crystallographic sites are resolved by means of 27Al 3QMAS technique. This product is able to sorb both carbon dioxide and methane at room temperature (4.4 mmol.g(-1) for CO2 and 1.95 mmol.g(-1) for CH4 at 10 bar) and hydrogen at 77 K (1.91 wt % under 3 bar).

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    • "be desorbed under flowing air [15]. This assumption is also in agreement with thermo gravimetric measurement (TGA) performed by Loiseau et al. and Yaghi et al. [12] [13] reporting that water molecules are adsorbed on the surface of MOF as well as on the positively charged metal sites inside and can be reversible removed upon heating without influencing the MOF structure leaving unsaturated metal sites unoccupied and available for other guest molecules. Moreover according to Yaghi et al. [13] the adsorption of molecules into MOFs with unsaturated metal sites depends not only on the size and shape of the guest molecules but also on their electronic affinity for the metal site. "
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