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. MOFs formed from 8-connecting nodes and 4-connecting linkers can have the flu, scu and csq topologies. Here we show design criteria for making the rare sqc topology and how topology can be used to generate distinct post-synthetic metalation sites.