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Metal-organic frameworks (MOFs) represent a unique class of porous materials with tremendous potential for diverse applications. A key factor contributing to their versatility is their ability to precisely introduce functional groups at specific positions within pores and crystals. This review explores two prominent strategies for achieving the positional functionalization of MOFs: post-synthetic ligand exchange (PSE) and MOF-on-MOF. In PSE, the existing ligands within solid-state MOFs can be selectively replaced by the desired functional groups in solution through ligand dynamics. This invasive functionalization provides a flexible approach to fine-tuning the surface of the MOFs with the target functionality. Conversely, MOF-on-MOF strategies are additive methodologies involving the controlled growth of one MOF layer onto another. The functionality of the core and shell (or surface) can be independently controlled. This review critically examines the examples, strengths, limitations, and applications of these strategies, emphasizing their significance in advancing the field of MOF functionalization and paving the way for tailored multifunctional materials with precise and specific properties.
Lee et al. (Mon,) studied this question.