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 EU5(III)(OH)(9)(H2O)(6)-(O2C-C2H2-CO2)(3)(.)9.5H(2)O, and MIL-80 or EU4III(OH)(4)(H2O)(5)(O2C-C2H2-CO2)(4)(.)4H(2)O, 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 I-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) Angstrom, by = 11.014(1) Angstrom, c = 13.247(1) Angstrom, beta = 119.162(1)degrees, and Z = 4. Crystal data for MIL-80: triclinic space group P (1) over bar with a = 10.5770(2) Angstrom, b = 10.6164(2) Angstrom, c = 14.9403(3) Angstrom, alpha = 91.624(1)degrees, beta = 91.120(1)degrees, gamma = 113.892(1)degrees, and Z = 2.