Department of Chemistry, University of California-Berkeley, Berkeley, California 94720, United States.
Kavli Energy NanoScience Institute at UC Berkeley, Berkeley, California 94720, United States.
Acc Chem Res. 2022 Mar 1;55(5):707-721. doi: 10.1021/acs.accounts.1c00740. Epub 2022 Feb 16.
The design and synthesis of permanently porous materials with extended cage structures is a long-standing challenge in chemistry. In this Account, we highlight the unique role of zeolitic imidazolate frameworks (ZIFs), a class of framework materials built from tetrahedral nodes connected through imidazolate linkers, in meeting this challenge and illustrate specific features that set ZIFs apart from other porous materials. The structures of ZIFs are characteristic of a variety of large, zeolite-like cages that are covalently connected with neighboring cages and fused in three-dimensional space. In contrast to molecular cages, the fusion of cages results in extraordinary architectural and chemical stability for the passage of gases and molecules through cages and for carrying out chemical reactions within these cages while keeping the cages intact. The combination of the advantages from both cage chemistry and extended structures allows uniquely interconnected yet compartmentalized void spaces inside ZIF solids, rendering their wide range of applications in catalysis, gas storage, and gas separation.While the field of ZIFs has seen rapid development over the past decade, with hundreds of ZIF structures built from dozens of different cages of varying composition, size, and shapes reported, rational approaches to their design are largely unknown. In this Account, we summarize a vast number of cages formed in reported ZIFs and then review how the thermodynamic factors and traditional guest-templating strategies from zeolites influence the formation of cages. We highlight how the link-link interactions perform in the ZIF formation mechanism and serve as a means to target the formation of frameworks containing cages of specific sizes with structures exhibiting a level of complexity as yet unachieved in discrete coordination cages. For example, the giant cage features a dimension of 46 Å and the complex cage is constructed from as many as 660 components.With the finding of these large and complex cages in ZIFs, we envision that the collection of cage structures will further be diversified by a mixed-linker approach utilizing a more complex combination of link-link interactions or by creating multivariant (MTV) systems that have been realized in other framework materials yet not widely employed in ZIFs. The more complicated cage structures can provide extra variations in chemical environments, and in addition to that, MTV systems can generate inhomogeneity inside each type of cage structure. The fused cages at such complexity that are difficult to be realized in solution environments will potentially enable more complex materials for smart applications.
具有扩展笼状结构的永久多孔材料的设计和合成是化学领域长期存在的挑战。在本专题介绍中，我们强调沸石咪唑酯骨架（ZIF）这一骨架材料在应对这一挑战方面的独特作用，ZIF 是一类由四面体节点通过咪唑配体连接而成的框架材料，并说明了将 ZIF 与其他多孔材料区分开来的特定特征。ZIF 的结构具有各种大型沸石样笼的特征，这些笼通过相邻笼的共价连接并在三维空间中融合。与分子笼不同，笼的融合导致气体和分子通过笼的传输以及在这些笼内进行化学反应的非凡的结构和化学稳定性，同时保持笼的完整。笼化学和扩展结构的优势相结合，允许在 ZIF 固体内部形成独特的互联但分隔的空隙空间，从而在催化、气体储存和气体分离等方面得到广泛应用。
尽管 ZIF 领域在过去十年中得到了快速发展，报道了数百种由数十种不同组成、尺寸和形状的笼构建的 ZIF 结构，但对其设计的合理方法在很大程度上仍不清楚。在本专题介绍中，我们总结了报道的 ZIF 中形成的大量笼，并回顾了热力学因素和沸石中的传统客体模板策略如何影响笼的形成。我们强调了链接相互作用在 ZIF 形成机制中的作用，并作为一种手段，针对具有特定尺寸笼的框架的形成，以及具有迄今为止在离散配位笼中未实现的复杂程度的结构。例如，巨型笼的尺寸为 46 Å，而复杂笼由多达 660 个组件构成。
随着在 ZIF 中发现这些大型和复杂的笼，我们设想通过混合配体方法进一步使笼结构多样化，该方法利用更复杂的链接相互作用组合，或通过创建已在其他框架材料中实现但在 ZIF 中尚未广泛应用的多变量（MTV）系统。更复杂的笼结构可以提供更多的化学环境变化，此外，MTV 系统可以在每种笼结构内产生不均匀性。在溶液环境中难以实现的如此复杂的融合笼可能会为智能应用提供更复杂的材料。
