Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, United States.
Department of Chemistry, University of California, Berkeley, California 94720, United States.
J Am Chem Soc. 2020 Mar 11;142(10):4705-4713. doi: 10.1021/jacs.9b11952. Epub 2020 Feb 26.
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 (MeNH)[ML] (M = Zn, Mn; HL = 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 C 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 p 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 p. Together, these results offer a potentially general synthetic strategy toward new materials with exotic metal-linker coordination modes.
含酰胺键的金属有机骨架通常具有出色的物理性质，但由于其强的金属-氮键，通过直接合成很难将其分离。在这里，我们报告了一种从其二羟基苯醌对应物通过后合成配体交换途径来获得金属二酰胺苯醌骨架的方法。母体化合物(MeNH)[ML]（M = Zn、Mn；HL = 2,5-二氯-3,6-二羟基-1,4-苯醌）在暴露于单质子化的 2,5-二氨基-3,6-二溴-1,4-苯醌或 2,5-二氨基-3,6-二氯-1,4-苯醌溶液中会发生配体交换，通过单晶到单晶反应进行。通过 NMR、拉曼和能量色散 X 射线（EDX）光谱的组合，证实了所得骨架中存在这两种类型的配体。此外，使用 C NMR 光谱定量测定了 Zn 骨架中配体交换的程度，空间分辨 EDX 光谱表明这两种类型的配体在晶体中均匀分布。最后，我们根据 p 值测量、考虑框架的溶解度和粉末 X 射线衍射分析提出了配体交换的推测机制。这项工作提供了在金属有机骨架中用不同供电子原子交换有机配体的第一种方法，并在此过程中展示了供电子原子酸度相差 11 个单位的配体之间的交换。总之，这些结果为具有奇特金属-配体配位模式的新材料提供了一种潜在的通用合成策略。
