Metal-organic frameworks (MOFs) are an emerging class of porous materials constructed from metal-containing nodes and organic linkers. Due to their structural and functional tunability as well as their ever-expanding application scope, MOFs have become one of the most fascinating class of materials for both scientists and engineers. MOFs provide ideal platforms to arrange various functional groups at atomic precision within the periodic lattice, leading to emergent synergistic effects in catalysis and gas adsorption. This requires the construction of MOFs from multiple metal nodes and/or organic linkers. However, the structural and compositional compilation of multi-component MOFs have posed a challenge for their synthesis. The complexity of MOFs is ultimately limited by the conventional "one-pot" synthetic method, which lacks control over the assembly of each framework component. By judicious kinetic control, we have developed stepwise synthetic strategies to build multi-component MOFs by "layer-on" molecular elaborations to preformed frameworks. A series of synthetic strategies have been developed which together form a synthetic toolkit through which a target multi-component MOF can be retro-synthetically designed and synthesized. The first section briefly summarized the development of MOFs to provide an overview on their structural design, synthesis and potential applications. In the second section, we focused on the synthesis of heterometallic MOFs using preformed heterometallic clusters to avoid undesired by products formed by other metal clusters. In the third section, the mixed-linker MOFs with crystallographically ordered structures were constructed using sequential linker installation. In the fourth section, we enriched the MOF synthetic toolkit by introducing linker labilization, in which selective linkers were exchanged, cleaved, and removed to create controlled defects in MOFs. The defective MOFs act as versatile platforms to create hierarchical structures and incorporate other coordinative assemblies. In the fifth section, we realized the "retrosynthesis" multi-component MOFs by sequentially applying the above mentioned synthetic methods under kinetic considerations. In summary, a series of synthetic methods were developed to construct multi-component MOFs with unprecedented complexity. These methods allow the rational design and synthesis of MOFs for specific applications including gas storage and separation, chemical sensing, energy harvesting and storage, catalysis, and biomedicine.
