Hydrothermal synthesis and structural characterization of a gallium pyromellitate Ga(OH)(btec)⋠0.5H2O, with infinite Ga-(μ2-OH)-Ga chains (MIL-61)

A new gallium carboxylate Ga(OH)(btec)⋅0.5H2O (MIL-61) was synthesized under mild hydrothermal conditions (200 °C, 24 hours) in the presence of 1,2,4,5-benzenetetracarboxylic (btec) acid and water. The crystal structure, characterized by means of Rietevelt refinement of powder XRD data, consists of trans chains of GaO4(OH)2 octahedra, connected to each other through a μ2-OH group. The three-dimensional framework is built up from these chains linked together via the organic molecules so delimiting the cavities where the water molecules are encapsulated. Analysis by solid state NMR (1H and 13C) has confirmed the presence within the structure of both water molecules and carboxylate moieties partially deprotonated. The structure of Ga(OH)(btec)⋅0.5H2O corresponds to that of MIL-61 obtained with vanadium replacing gallium.Crystal data for Ga4(OH)4((HO2C)2C6H4(CO2)2)4⋅2H2O: a=14.8325(10)Å, b=6.7792(10)Å, c=10.6726(10)Å, V=1073.2(2)Å3, Pnma (no 62).