Topological analysis and control of post-synthetic metalation sites in Zr-based metal-organic frameworks

The design criteria needed for the formation of the sqc metal-organic framework (MOF) topology, from an 8-connecting node and a 4-connecting linker, are unclear due to a limited number of reports. After recently reporting the MOF UAM-1000 (UAM = University of Adelaide Material), which has this rare sqc topology, we present a study that explores the effect of flexible tetrapyrazole carboxylate linker structure metrics on the topology of Zirconium-based MOFs (Zr-MOFs). By modifying the linker length and width, three new Zr-MOFs (UAM-10, UAM-11, and UAM-1002) were synthesized and characterized. The study reveals that linker dimensions influence the accessible conformations, and along with fine-tuning of synthetic conditions, allow control over MOF topology. Additionally, linker flexibility plays a crucial role in the formation of the sqc over the more common csq topology. Finally, the presence of free bis-pyrazolyl groups in the reported MOFs allowed us to evaluate the potential for post-synthetic metalation (PSMet). UAM-10 and UAM-11 are too rigid, the pyrazole groups lack the appropriate arrangement and therefore these materials do not undergo PSMet. In contrast, UAM-1002 with its scu topology exhibits the right quanta of flexibility needed for successful PSMet, making it a promising platform for studying the chemistry of anchored organometallic complexes. Moreover, the different topology for UAM-1002 versus UAM-1000 changes the nature of the PSMet site (bidentate versus a tetradentate site) despite these being made from the same node and linker building blocks.