Tandem\nPostsynthetic Metal Ion and Ligand Exchange in Zeolitic Imidazolate\nFrameworks

Abstract

Herein, we report a general postsynthetic\nexchange (PSE) approach to introduce a redox-active transition metal,\nspecifically Mn­(II), into “inert” zeolitic imidazolate\nframeworks (ZIFs), a subclass of metal–organic frameworks (MOFs).\nIt is shown that metal ion PSE occurs in ZIF-71 (<b>RHO</b> topology)\nand ZIF-8 (<b>SOD</b> topology) under ambient conditions. The\nmetal exchanged ZIFs are the first porous, Mn­(II)-based ZIFs and a\nrare example of ZIFs with two transition metal centers in a single\nlattice. Exchanged materials are characterized by scanning electron\nmicroscopy-energy dispersed X-ray spectroscopy (SEM-EDX), aerosol\ntime-of-flight mass spectrometry (ATOFMS), X-ray fluorescence spectroscopy\n(XRF), and Brunauer–Emmett–Teller (BET) surface area\nanalysis. In addition, stepwise “tandem” PSE strategies\nare described to exchange of metal ions and organic linkers consecutively\nin ZIFs. These findings are important for probing the chemical dynamics\nof ZIFs, despite their high crystallinity and robustness, and inspire\nthe more widespread use of PSE to prepare multimetallic and multifunctional\nMOFs.