Structural transformations in metal-organic frameworks (MOFs): Mechanisms, stimuli-responsiveness, and emerging applications

Metal-organic frameworks (MOFs) represent a category of crystalline porous materials that have attracted considerable interest owing to their structural flexibility and capacity to undergo reversible transformations in response to external stimuli. This review examines the underlying mechanisms that facilitate these structural changes, the various types of stimuli capable of inducing them, and the wide-ranging applications that capitalize on these dynamic properties. The discussion elucidates that the flexibility inherent in MOFs derives from several factors, including the characteristics of the metal cluster, the coordination geometry, the rigidity or flexibility of the organic linkers, and the overall topology of the framework. It is emphasized that minor alterations in these molecular-level attributes can result in significant variations in the structural behavior of MOFs, encompassing phenomena such as breathing, gate opening, and both negative and positive thermal expansion. Moreover, the review explores the experimental and computational methodologies employed to investigate MOF flexibility, incorporating in situ characterization techniques and molecular modeling approaches. It highlights how the interplay between framework design, guest interactions, and defect engineering can be strategically utilized to develop stimuli-responsive MOFs with customized functionalities suitable for applications in areas such as gas separation, gas storage, and sensing. In conclusion, the review underscores the importance of comprehending and manipulating structural transformations in MOFs, a consideration that has emerged as a key element in contemporary materials science and engineering.