An open-framework rare-earth acetylenedicarboxylate: MIL-95, Eu(III)2(H2O)2(CO3)2.{O2C-C2-CO2}.{H2O}x

The first three-dimensional rare-earth acetylenedicarboxylate solid, MIL-95 (MIL = Material Institut Lavoisier), has been isolated and its structure solved from single-crystal X-ray diffraction data. Its two-dimensional inorganic subnetwork, built up from chains of edge-sharing nine-coordinated europium-capped square antiprisms and carbonate moieties, is pillared by the acetylenedicarboxylate groups. This leads to an open framework where small pores are filled with water molecules interacting with terminal water bound to the metal centers. TGA and X-ray thermodiffractometry show that dehydration leads to an irreversible pore contraction. The whole structure collapses above 230 degrees C. Crystal data for MIL-95: orthorhombic space group Pba2 (No. 32), with a = 7.6762(2) A, b = 17.8448(4) A, and c = 4.8105(2) A.