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 (H 2 O) 6 (O 2 C−C 2 H 2 −CO 2 ) 3 ·9.5H 2 O, and MIL-80 or Eu III 4 (OH) 4 (H 2 O) 5 (O 2 C−C 2 H 2 −CO 2 ) 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 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 C 2/ m with a = 25.954(1) Å, b = 11.014(1) Å, c = 13.247(1) Å, β = 119.162(1)°, and Z = 4. Crystal data for MIL-80: triclinic space group P 1̄ with a = 10.5770(2) Å, b = 10.6164(2) Å, c = 14.9403(3) Å, α = 91.624(1)°, β = 91.120(1)°, γ = 113.892(1)°, and Z = 2.