Thorium Terephthalates Coordination Polymers Synthesized in Solvothermal DMF/H2O System

A series of thorium-based terephthalates have been solvothermaly synthesized in N,N-dimethylformamide (DMF) with different amounts of water and various temperatures (100–150 °C). Without the addition of water, the Th–H2bdc–DMF system gives rise to the formation of two phases, Th­(bdc)2­(DMF)2 (1) and Th6O4(OH)4­(H2O)6­(bdc)6·6DMF·12H2O (3) (bdc = 1,4-benzenedicarboxylate or terephthalate). Their structures are built up of isolated thorium centers ThO8(DMF)2 for (1) and the hexanuclear core Th6O4(OH)4­(H2O)6 for (3). The latter adopts the UiO-66 metal–organic framework topology and exhibits a very high porosity for an actinides-based porous material (BET surface up to 730(6) m2·g–1). The synthesis of (3) is also favored upon adding water. However, for pure aqueous solutions or for a very low amount of water, a third solid Th­(bdc)2 (2) crystallizes and contains thorium monomers ThO8. The main similitude with the parent system dedicated to tetravalent uranium concerns the possibility to stabilize the An6O8(H2O)6 core by terephthalate linkers and to reproduce An­(bdc)2­(DMF)2 for both actinides U4+ and Th4+. The thermal treatment of the latter shows a structural transition into the crystalline Th­(bdc)2 (2) solid.