The stability of Zirconium based metal–organic frameworks (Zr-MOFs) makes them among the most studied MOFs in the past decade. The Zr6 secondary building units (SBUs) are very versatile. The connectivity of Zr6 SBUs can be easily altered; a variety of connectivities have been demonstrated, such as 6-, 8-, 10-, and 12-connected nodes. Recently, more exotic odd 9- and 11-connect SBUs were also reported. Zr6 SBUs with less than 12 connecting number usually contain missing linker sites which are commonly coordinated with water or hydroxyl groups. More recently, the lowest connectivity, 4-connected, of Zr6 SBU has been reported. Though these connectivities vary, the common factor between them is that their connectivities are all below 12. No examples of connectivity greater than 12 have been reported to date. Recently, we have taken the first step to explore higher connectivities of the Zr6 SBU by achieving a 14-connected Zr6 SBU. This was accomplished through the post-synthetic linker insertion of a new Zr-MOF, named WSU-5 (WSU stands for Washington State University). The insertion of a short linear linker, benzenedicarboxylic acid, resulted in the connection of adjacent Zr6 SBUs from the two independent nets, which gave rise to a new MOF, named WSU-6 which possesses the new 4,12-connected mjh topology. Interestingly, when the longer linker, naphthalenedicarboxylic acid (NDC), was inserted, the NDC linkers not only linked the adjacent Zr6 clusters from the two nets but also joined the neighboring Zr6 SBUs within the same net. The two additional linkages to the SBUs yielded a new MOF, WSU-7, with a 14-connected Zr6 SBU. The NDC inserted MOF was determined to possess the new 4,14-connected jkz topology. The insertion of linkers not only changed the connectivity of the nodes and made new topologies, but also altered the luminescent properties of the resulting MOFs. Post-synthetic linker insertion has proven to be a powerful tool to alter the connectivity of SBUs and develop new topologies as well as tune properties of MOFs.

Old linkers new tricks: Evolution of 14-Connect Zr6 secondary building units

2019 Fall National Meeting

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