Structural Analysis of F/OH Distribution in a Hybrid Open-Framework Fluorinated Gallium Oxalate-Phosphate Templated by 1,3Diaminopropane (MIL-90)

A new gallium oxalate-phosphate compound MIL-90 or Ga5(PO4)4(C2O4)F2(OH)2·1.5N2C3H12 was synthesized under mild hydrothermal conditions (180 °C, 24 h) by using 1,3-diaminopropane as a structure-directing agent. Its structure was characterized by means of single-crystal XRD analysis and multinuclear solid state NMR; it consists of the corner-shared connection of PO4, GaO4 tetrahedra with GaO5X and GaO2X4 octahedra where X = OH or F. 19F and 31P MAS NMR showed statistical distribution of the fluorine and hydroxyl group on the bridging sites between the two types of the octahedrally coordinated gallium atoms. 71Ga MAS NMR indicated two different kinds of gallium within the structure, with tetrahedral and octahedral environment. The gallium octahedra GaO5Fx(OH)1-x (x (almost equal)0.72) are linked together through the oxalate anions, which results in the formation of a layerlike structure comprising the oxalate bridging dimer of GaO5Fx(OH)1-x (x (almoast equal)0.72) and GaO4 tetrahedra connected to the phosphate anions. The resulting sheets are stacked along the c axis and connected to each other via the GaO2X4 (X = OH or F) octahedra. This specific arrangement generates a three-dimensional framework with intersecting channels bound by 10 polyhedra (4.5 * 4.5 (angstrom)) running along [100] and [010]. Within the tunnels are located the diprotonated 1,3-diaminopropane species, confirmed by 1H MAS and 13C CPMAS experiments, which preferentially interact via hydrogen bond with the terminal fluorine or hydroxyl group of gallium octahedra GaO2X4 (X = OH or F). Crystal data for Ga5(PO4)4(C2O4)F2(OH)2·1.5N2C3H12: a = 8.1217(6) (angstrom), b = 8.9601(6) (angstrom), c = 10.4611(8) (angstrom), (alpha)= 111.930(1)°, ?= 103.655(1)°, (gamma)= 101.903(1)°, V = 648.59(8) (angstrom)3, PI(No.2), Z =1, R1 = 0.0598, wR2 = 0.1568 for 3247 reflections I > 2(sigma)(I).