We report a postsynthetic strategy and its implementation to make covalent organic frameworks (COFs) with irreversible hydrazide linkages. This involved the synthesis of three 2D and 3D hydrazine-linked frameworks and their partial oxidation. The linkage synthesis and functional group transformation─hydrazine and hydrazide─were evidenced by ¹⁵N multi-CP-MAS NMR. In addition, the isothermal water uptake profiles of these frameworks were studied, leading to the discovery of one hydrazine-hydrazide-linked COF suitable for water harvesting from air in arid conditions. This COF displayed characteristic S-shaped water sorption profiles, a steep pore-filling step below 18% relative humidity at 25 °C, and a total uptake capacity of 0.45 g g^–1. We found that even small changes made on the molecular level can lead to major differences in the water isotherm profiles, therefore pointing to the utility of water sorption analysis as a complementary analytical tool to study linkage transformations.

中文翻译：

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用于集水的肼-酰肼连接的共价有机框架

我们报告了一种合成后策略及其实施，以制造具有不可逆酰肼键的共价有机框架 (COF)。这涉及三个 2D 和 3D 肼连接框架的合成及其部分氧化。通过¹⁵ N 多 CP-MAS NMR 证明了键合合成和官能团转化——肼和酰肼。此外，研究了这些框架的等温吸水曲线，从而发现了一种适用于在干旱条件下从空气中收集水的肼-酰肼连接的 COF。该 COF 显示出特征性的 S 形吸水曲线，在 25 °C 相对湿度低于 18% 时具有陡峭的孔隙填充步骤，总吸收能力为 0.45 gg ^–1. 我们发现，即使是在分子水平上的微小变化也会导致水等温线分布的重大差异，因此指出吸水分析作为研究连接转换的补充分析工具的效用。