Systematic Investigations of the Transition between Framework Topologies in Ce/Zr-MOFs

1-H-Pyrazole-3,5-dicarboxylic acid (H2PZDC), a small, strongly bent linker molecule with an angle of 147.4° between the carboxylate groups, was used in the synthesis of metal organic frameworks (MOFs) with fcu, bcu and reo topology. In systematic studies of the chemical system Ce4+/Zr4+/H2PZDC/HCOOH, their fields of formations were established. The decisive factors for the product formation and hence the transition between the framework topologies are the HCOOH/metal ratio and the molar ratio of Ce4+/Zr4+ employed in the synthesis. All title compounds crystallize with the well-known hexanuclear cluster {M6(μ3-O)4(μ3-OH)4(−CO2)n}, with n = 8 or 12 and M = Ce4+ and Zr4+, as the inorganic building unit (IBU). Connection through 12 or eight linker molecules leads to three framework topologies: fcu, bcu, and reo, respectively. The dominant phase observed in this system crystallizes with reo topology and is known as DUT-67. The pure Zr-MOF of composition [Zr6(μ3-O)4(μ3-OH)4(PZDC)4(OH)2(H2O)2] (Zr-DUT-67-PZDC) a...