title: MIL-50, an open-framework GaPO with a periodic pattern of small water ponds and dry rubidium atoms: a combined XRD, NMR, and computational study.
abstract: A new fluorinated gallium phosphate, MIL-50, has been synthesized under mild hydrothermal conditions using 1,6-diaminohexane. The chemical formula of MIL-50 is Rb(2)Ga(9)(PO(4))(8)(HPO(4))(OH)F(6).2N(2)C(6)H(18).7H(2)O. The structure is a network of hexameric units of Ga(3)(PO(4))(3)F(2) and Ga(3)(PO(4))(2)(HPO(4))F(3) via corner sharing. It creates a three-dimensional open-framework delimiting 6- and 18-ring channels running along the c axis. The diprotonated 1,6-diaminohexane and water molecules are trapped within the 18-ring pores, whereas the rubidium cations reside in the 6-ring ones. A double quantum (31)P NMR experiment and partial charge calculations indicate that water molecules are present under the form of periodic small clusters, lowering the multiplicity of one phosphorus site, P3. Though water hops within the clusters, the motion leaves the water pattern periodic. Rubidium is so tightly embedded into the framework that water moving in the large 18-ring channels does not reach it, leaving it therefore dry. The crystal framework may be ascribed to the orthorhombic space group Cmc2(1) (n degrees 36), a = 32.1510(2), b = 17.2290(3), c = 10.2120(1) A. The periodic water pattern has a different symmetry than that of the framework. A method has been devised to superpose the two sublattices that coexist in the same unit cell in order to have full occupancy of each site and to perform Madelung summations. This original method is of general interest for most zeolitic materials exhibiting a different symmetry for the framework and the template sublattices.
authors.affiliation: Institut Lavoisier, UMR CNRS 8637, Université de Versailles St Quentin en Yvelines, 45, Avenue des Etats-Unis, 78035 Versailles Cedex, France.
authors.forename: Lionel
authors.initials: L
authors.lastname: Beitone
authors.forename: Jérôme
authors.initials: J
authors.lastname: Marrot
authors.forename: Thierry
authors.initials: T
authors.lastname: Loiseau
authors.forename: Gérard
authors.initials: G
authors.lastname: Férey
authors.forename: Marc
authors.initials: M
authors.lastname: Henry
authors.forename: Clarisse
authors.initials: C
authors.lastname: Huguenard
authors.forename: Axel
authors.initials: A
authors.lastname: Gansmuller
authors.forename: Francis
authors.initials: F
authors.lastname: Taulelle