Hydrothermal Synthesis, Structure Determination, and Thermal Behavior of New Three-Dimensional Europium Terephthalates: MIL-51_LT,HT and MIL-52 or Eu₂ⁿ(OH)_x(H₂O)_y(O₂C−C₆H₄−CO₂)_z (n = III, III, II; x = 4, 0, 0; y = 2, 0, 0; z = 1, 1, 2)

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-51 LT or Eu 2 III (H 2 O) 2 (OH) 4 (O 2 C−C 6 H 4 −CO 2 ) and MIL-51 HT or Eu 2 III (OH) 4 (O 2 C−C 6 H 4 −CO 2 ) contain only trivalent europium, while MIL-52 or Eu II (O 2 C−C 6 H 4 −CO 2 ) 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-51 LT,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-51 LT and MIL-51 HT are correlated. Crystal data for MIL-51 LT and MIL-51 HT: triclinic space group P 1̄ (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) Å 3 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) Å 3 . 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) Å 3 .