Synthesis and Characterization of MIL-79 and MIL-80: Two New Luminescent Open-Framework Rare-Earth Dicarboxylates with Unusual 1D Inorganic Subnetworks

Two new three-dimensional europium(III) dicarboxylates, MIL-79 or Eu(III)5(OH)9(H2O)6(O2C-C2H2-CO2)3·9.5H2O, and MIL-80 or EuIII4(OH)4(H2O)5(O2C-C2H2-CO2)4·4H2O, have been obtained under hydrothermal conditions. Both structures, which have been determined using either X-ray powder or single-crystal diffraction data, are built-up from unusual complex chains made from clusters of eight-, nine-, and ten-coordinated europium(III) polyhedra linked through fumarate and maleate dianions. This creates three-dimensional structures with either 1-D large elongated pore channels (MIL-79) or cages (MIL-80) filled in both cases with free water molecules which interact with terminal water molecules or apical oxygen atoms from the carboxylates. The thermal behavior of MIL-79 has been investigated using TGA and X-ray thermodiffractometry and reveals that its dehydration leads to an irreversible pore contraction. Study of the luminescence properties of the yttrium (III) form of MIL-79 doped with europium(III) reveals a significant red-emission upon VUV radiation. Crystal data for MIL-79: monoclinic space group C2/m with a = 25.954(1) (anstrom), b = 11.014(1) (anstrom), c = 13.247(1) (anstrom), (beta)= 119.162(1)°, and Z= 4. Crystal data for MIL-80: triclinic space group PI with a = 10.5770(2) (anstrom), b = 10.6164(2) (anstrom), c = 14.9403(3) (angstrom), (alpha)= 91.624(1)°, (beta)= 91.120(1)°, (gamma)= 113.892(1)°, and Z = 2.