Single-Crystalline Hydrogen-Bonded Crosslinked Organic Frameworks and Their Dynamic Guest Sorption
Single-Crystalline Hydrogen-Bonded Crosslinked Organic Frameworks and Their Dynamic Guest Sorption
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DOI：
10.1021/accountsmr.2c00173
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发表时间：
2022-10-27
影响因子：
14.6
通讯作者：
Ke，Chenfeng
中科院分区：
文献类型：
--
作者：
Samanta，Jayanta;Zhang，Yunjia;Ke，Chenfeng
多孔有机框架材料由周期性排列的分子实体构成，为各种应用提供了化学定制的微环境来吸收分子和离子。从根本上了解这些多孔有机材料的微环境──从孔径、形状、动力学到潜在的底物结合位点──对多孔有机材料的合理设计至关重要。这些多孔有机材料的固态结构，如共价有机框架（COFs），可以提供明确的原子级结构细节。然而，将这些材料合成为可以通过单晶x射线衍射（SCXRD）或旋转电子衍射（RED）分析完全表征的单晶仍然具有挑战性。此外，单晶度、永久孔隙度和良好的化学稳定性的平衡需要在合成过程中对分子构建块的组装和共价交联进行精细的控制。本文讨论了具有平衡单晶度和高化学稳定性的氢键交联有机骨架（HCOFs）的发展。HCOFs是通过氢键预组织的共价交联分子晶体获得的。由于双氢键网络和共价交联，HCOFs可以在客体吸附时通过破坏氢键而变形，随后通过客体解吸重新建立氢键网络恢复其原始形态。因此，HCOFs可以根据框架-衬底相互作用动态调整孔径。在讨论中，我们通过比较它们获得高结晶度的合成方法，将HCOFs与COFs和单晶2D聚合物联系起来。合成HCOFs的方法允许使用各种灵活的构建块和连接基序，这在目前的COFs和2D聚合物设计制度中基本上是避免的。我们还通过强调它们构建具有大空隙的氢键网络的共同设计原则，绘制了HCOFs和氢键有机框架（HOFs）之间的联系。与氢键前驱体晶体相比，用共价键加强氢键网络可以增强HCOFs的化学稳定性和结构稳定性。此外，我们还强调了HCOFs的结构解析往往需要将SCXRD分析和实验证据相结合，并对方法和挑战进行了深入的讨论。具体步骤如下：(1)将缩聚速率与成核速率相匹配，合成单晶COFs，并用SCXRD/RED对其进行分析；(2)通过拓扑化学反应获得单晶聚合物和网络；(3)利用高定向氢键构建块构建具有设计空隙的hof；(4)通过单体晶工程和单晶到单晶（SCSC）合成制备HCOFs，并研究其独特的动态吸附行为。我们希望这篇论文能够启发研究人员拓展合成方法，以推进具有详细固态结构的HCOFs，并设计具有动态吸附能力的多孔有机框架材料，以提高其在分子存储、分离、催化等方面的应用性能。
ConspectusPorous organic framework materials constructed by periodically aligned molecular entities offer chemically tailored microenvironments to absorb molecules and ions for various applications. Fundamentally understanding the microenvironments of these porous organic materials─from pore size, shape, and dynamics to potential substrate binding sites─is critical for the rational design of porous organic materials. The solid-state structures of these porous organic materials, such as covalent organic frameworks (COFs), can provide unambiguous atomic-level structural details. However, it remains challenging to synthesize these materials as single crystals that can be fully characterized by single-crystal X-ray diffraction (SCXRD) or rotational electron diffraction (RED) analysis. In addition, the balance of single crystallinity, permanent porosity, and good chemical stability requires delicate control of the assembly of the molecular building blocks and covalent crosslinking during synthesis. In this Account, we discuss the development of hydrogen-bonded crosslinked organic frameworks (HCOFs) possessing balanced single crystallinity and high chemical stability. HCOFs are obtained through covalently crosslinking molecular crystals that are preorganized via hydrogen bonding. Due to the dual hydrogen-bonded network and covalent crosslinking, HCOFs can deform upon guest adsorption by breaking the hydrogen bonds and subsequently restore their original form through the desorption of guests by re-establishing the hydrogen-bonded networks. Thus, HCOFs can dynamically adjust their pore sizes according to the framework–substrate interactions. In the discussion, we link HCOFs with COFs and single-crystalline 2D polymers by comparing their synthetic approaches to accessing high crystallinity. The method to synthesize HCOFs allows for the employment of various flexible building blocks and linking motifs that are largely avoided in the current design regimes of COFs and 2D polymers. We also draw the connections between HCOFs and hydrogen-bonded organic frameworks (HOFs) by highlighting their shared design principles for constructing hydrogen-bonding networks with large voids. Compared to their hydrogen-bonded precursor crystals, reinforcing the hydrogen-bonded networks with covalent linkages endows HCOFs with enhanced chemical and structural stability. In addition, we emphasize that the structure elucidation of HCOFs often requires combined SCXRD analysis and experimental evidence, with the methods and challenges thoroughly discussed. The details are presented in the following sequence: (1) synthesizing single-crystalline COFs by matching the polycondensation rate to the nucleation rate and their subsequent analyses by SCXRD/RED; (2) obtaining single-crystalline polymers and networks through topochemical reactions; (3) constructing HOFs with designed voids using highly directional hydrogen bonding building blocks; and (4) developing HCOFs via monomer crystal engineering followed by single-crystal to single-crystal (SCSC) synthesis and studying their unique dynamic guest sorption behaviors. We hope this Account will inspire researchers to expand the synthetic methods for advancing HCOFs with detailed solid-state structures, as well as designing porous organic framework materials with dynamic sorption capabilities to enhance their performance for applications in molecular storage, separation, catalysis, etc.