Synthesis of MIL-102, a chromium carboxylate metal-organic framework, with gas sorption analysis

A new three-dimensional chromium(III) naphthalene tetracarboxylate, (Cr3O)-O-III(H2O)(2)F{C10H4-(CO2)4}(1.5).6H(2)O (MIL-102), has been synthesized under hydrothermal conditions from an aqueous mixture of Cr(NO3)(3).9H(2)O, naphthalene-1,4,5,8-tetracarboxylic acid, and HF. Its structure, solved ab initio from X-ray powder diffraction data, is built up from the connection of trimers of trivalent chromium octahedra and tetracarboxylate moieties. This creates a three-dimensional structure with an array of small one-dimensional channels filled with free water molecules, which interact through hydrogen bonds with terminal water molecules and oxygen atoms from the carboxylates. Thermogravimetric analysis and X-ray thermodiffrac-tometry indicate that MIL-102 is stable up to similar to 300 degrees C and shows zeolitic behavior. Due to topological frustration effects, MIL-102 remains paramagnetic down to 5 K. Finally, MIL-102 exhibits a hydrogen storage capacity of similar to 1.0 wt% at 77 K when loaded at 3.5 MPa (35 bar). The hydrogen uptake is discussed in relation with the structural characteristics and the molecular simulation results. The adsorption behavior of MIL-102 at 304 K resembles that of small-pore zeolites, such as silicalite. Indeed, the isotherms of CO2, CH4, and N-2 show a maximum uptake at 0.5 MPa, with no further significant adsorption up to 3 MPa. Crystal data for MIL-102: hexagonal space group P (6) over bar (No. 169), a = 12.632(1) angstrom, c = 9.622(1) angstrom.