Metal–Diamidobenzoquinone Frameworks via Post-Synthetic Linker Exchange

Metal–organic frameworks with amidic linkers often exhibit exceptional physical properties, but, owing to their strong metal–nitrogen bonds, are exceedingly challenging to isolate through direct synthesis. Here, we report a route to access metal–diamidobenzoquinone frameworks from their dihydroxobenzoquinone counterparts via postsynthetic linker exchange. The parent compounds (Me₂NH₂)₂[M₂L₃] (M = Zn, Mn; H₂L = 2,5-dichloro-3,6-dihydroxo-1,4-benzoquinone) undergo linker exchange upon exposure to a solution of monodeprotonated 2,5-diamino-3,6-dibromo-1,4-benzoquinone or 2,5-diamino-3,6-dichloro-1,4-benzoquinone, proceeding through single-crystal-to-single-crystal reactions. The presence of both types of linker in the resulting frameworks is confirmed by a combination of NMR, Raman, and energy-dispersive X-ray (EDX) spectroscopies. Moreover, the extent of linker exchange in the Zn frameworks is quantified using ¹³C NMR spectroscopy, and spatially resolved EDX spectroscopy reveals the two types of linker to be homogeneously distributed within a crystal. Finally, we propose a tentative mechanism of linker exchange based on pK_a measurements, considerations of framework solubility, and powder X-ray diffraction analysis. This work provides the first method to exchange organic linkers with different donor atoms in metal–organic frameworks and in doing so demonstrates exchange between linkers with donor atoms differing in acidity by a remarkable 11 units of pK_a. Together, these results offer a potentially general synthetic strategy toward new materials with exotic metal-linker coordination modes.