title: 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.
abstract: 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.
authors.affiliation: Institut Lavoisier (UMR CNRS 8180), Porous Solids Group, Université de Versailles Saint Quentin en Yvelines, 45, Avenue des Etats-Unis, 78035 Versailles, France.
authors.forename: Christophe
authors.initials: C
authors.lastname: Volkringer
authors.forename: Mohamed
authors.initials: M
authors.lastname: Meddouri
authors.forename: Thierry
authors.initials: T
authors.lastname: Loiseau
authors.forename: Nathalie
authors.initials: N
authors.lastname: Guillou
authors.forename: Jérôme
authors.initials: J
authors.lastname: Marrot
authors.forename: Gérard
authors.initials: G
authors.lastname: Férey
authors.forename: Mohamed
authors.initials: M
authors.lastname: Haouas
authors.forename: Francis
authors.initials: F
authors.lastname: Taulelle
authors.forename: Nathalie
authors.initials: N
authors.lastname: Audebrand
authors.forename: Michel
authors.initials: M
authors.lastname: Latroche