The opportunity to generate functional solids with defined properties by deliberate design has not been materialized in traditional solid-state chemistry over many decades. The emergence of metal-organic frameworks (MOFs), permanently porous, crystalline solids with defined metrics, has allowed for studying design, synthesis, and properties, which then translated into new applications. Aggregates of metal ions stitched together by multidentate functional groups form such metal oxide clusters and represent the nodes of MOFs. These clusters, termed secondary building units (SBUs), are decorated with organic moieties that provide directionality and can be linked through geometric principles into extended nets using organic molecules (spacers). This concept of reticular chemistry has afforded permanently porous MOFs, and has resulted in over 20,000 structures over the past 20 years. However, there are still only a limited number of symmetric, discrete SBUs commonly used to design and synthesize MOFs. We herein introduce the most important SBUs that have emerged over time together with prototypal MOF structures and their fundamental applications. Both the discovery and the scientific impact will be highlighted alongside advantages and/or drawbacks. In addition, an outlook will be given on how the combination of multiple SBUs can lead to heterogeneous but ordered materials with higher complexity and functionality.

中文翻译：

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设计为何如此重要：从装饰的金属氧化物簇到功能性的金属有机框架。

数十年来，通过传统的设计方法来生成具有定义的特性的功能性固体的机会在传统的固态化学中尚未得到实现。金属有机骨架（MOF）的出现是具有确定指标的永久多孔晶体固体，可以研究设计，合成和性能，然后转化为新的应用。通过多齿官能团缝合在一起的金属离子的聚集体形成了此类金属氧化物簇，并代表了MOF的节点。这些簇称为二级建筑单元（SBU），由提供定向性的有机部分装饰，可以使用有机分子（间隔子）通过几何原理连接成扩展的网。网状化学的概念提供了永久性的多孔MOF，并已导致20多个 在过去20年中有000座建筑物。但是，仍然只有有限数量的对称，离散SBU通常用于设计和合成MOF。我们在这里介绍随着时间的流逝而出现的最重要的SBU，以及原型MOF结构及其基本应用。发现和科学影响将与优点和/或缺点一并强调。此外，将展望多个SBU的组合如何导致具有更高复杂性和功能性的异质但有序的材料。我们在这里介绍随着时间的流逝而出现的最重要的SBU，以及原型MOF结构及其基本应用。发现和科学影响将与优点和/或缺点一并强调。此外，将展望多个SBU的组合如何导致具有更高复杂性和功能性的异质但有序的材料。我们在这里介绍随着时间的流逝而出现的最重要的SBU，以及原型MOF结构及其基本应用。发现和科学影响将与优点和/或缺点一并强调。此外，将展望多个SBU的组合如何导致具有更高复杂性和功能性的异质但有序的材料。