Hydrothermal Synthesis, Structure Determination, and Thermal Behavior of New Three-Dimensional Europium Terephthalates: MIL-51<sub>LT,HT</sub> and MIL-52 or Eu<sub>2</sub><i><sup>n</sup></i><sup></sup>(OH)<i><sub>x</sub></i>(H<sub>2</sub>O)<i><sub>y</sub></i>(O<sub>2</sub>C−C<sub>6</sub>H<sub>4</sub>−CO<sub>2</sub>)<i><sub>z</sub></i> (<i>n</i> = III, III, II; <i>x</i> = 4, 0, 0; <i>y</i> = 2, 0, 0; <i>z</i> = 1, 1, 2)
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Three-dimensional europium terephthalates have been obtained under hydrothermal conditions and their structures solved using either X-ray powder diffraction or single-crystal data. MIL-51LT or Eu2III(H2O)2(OH)4(O2C−C6H4−CO2) and MIL-51HT or Eu2III(OH)4(O2C−C6H4−CO2) contain only trivalent europium, while MIL-52 or EuII(O2C−C6H4−CO2) involves only europium(II) metallic centers. Their structures are built up from eight- or nine-coordinated europium polyhedra and terephthalate anions, creating pillared structures. Inorganic layers of MIL-51LT,HT are closely related to those of europium hydroxide. Oxygen atoms of the inorganic sheets are either water molecules, hydroxyl groups, or oxygen atoms of the dicarboxylates. In the case of MIL-52, anions are oxygen atoms from the organic moities. In both structures, elongated hydrophobic channels are present but with no real porosity. Thermogravimetric analysis and X-ray thermodiffractometry have shown that MIL-51LT and MIL-51HT are correlated. Crystal data for MIL-51LT and MIL-51HT: triclinic space group P1̄ (No. 2) with a = 13.190(1) Å, b = 7.185(1) Å, c = 3.718(1) Å, α = 120.452(1)°, β = 87.630(1)°, γ = 97.650(1)°, V = 300.96(1) Å3 and a = 11.9691(1) Å, b = 6.2569(1) Å, c = 3.6773(2) Å, α = 91.03(1)°, β = 97.53(1)°, γ = 91.01(1)°, V = 273.6(1) Å3. Crystal data for MIL-52: orthorhombic space group Pbca (No. 61) with a = 7.4052(2) Å, b = 10.1144(3) Å, c = 18.7512(1) Å, V = 1404.45(7) Å3.
