Investigation of the Kinetic Stabilization of a Ce4+‐based MOF by in‐situ Powder X‐ray Diffraction

Abstract

We herein investigated the synthesis of the Ce4+‐based metal‐organic framework [Ce6(μ3‐O)4(μ3‐OH)4(PZDC)4(OH)4(H2O)4] denoted as Ce‐DUT‐67‐PZDC (where DUT stands for Dresden University of Technology and PZDC2– stands for 3,5‐pyrazoledicarboxylate) by in‐situ powder X‐ray diffraction methods under solvothermal conditions using synchrotron radiation. It was observed that the obtained MOF is rapidly formed between 120 and 140 °C, but only as an intermediate product in this preparative system. After prolonged reaction times, Ce4+ is reduced to Ce3+ and reacting with formic acid from the reaction mixture to form the final product [Ce(O2CH)3]. During the formation of trivalent cerium formate, the Ce(IV)‐MOF completely re‐dissolves. Based on the composition of the reaction mixture and the recorded data, a plausible reaction mechanism was established. This mechanistic scheme includes a reversible precipitation of the Ce(IV)‐MOF under the given conditions and the reduction of Ce4+ by formate anions generated via hydrolysis of the solvent dimethylformamide.