Secondary building units of MOFs

This chapter introduces various metal-cluster entities, the secondary building units (SBUs), to construct metal-organic frameworks (MOFs) with robust architectures. In MOFs, metal ions and linkers sustain a defined coordination geometry within the SBUs, which leads to the formation of predictable framework structures by virtue of reticular chemistry. Knowledge about these SBUs and the resulting framework topology provides fast opportunity to synthesis of task-specific materials with desired properties. Herein, we detail different kinds of SBUs, depending on the nature of the organic functionality, and classify them according to their points of extension, the number of possible connections between them through organic linkers. This summary includes single metal nodes, metal-carboxylate clusters, metal-nitrogen SBUs, metal-organic polyhedra, and infinite rod SBUs. In this chapter, some material properties are highlighted to underline the importance of crystalline MOFs that preserve structural integrity and permanent porosity. Particular MOFs will be discussed with respect to biomedical applications.