Understanding MOF Flexibility: An Analysis Focused on Pillared Layer MOFs as a Model System

Flexible porous frameworks are at the forefront of materials research. A unique feature is their ability to open and close their pores in an adaptive manner induced by chemical and physical stimuli. Such enzyme‐like selective recognition offers a wide range of functions ranging from gas storage and separation to sensing, actuation, mechanical energy storage and catalysis. However, the factors affecting switchability are poorly understood. In particular, the role of building blocks, as well as secondary factors (crystal size, defects, cooperativity) and the role of host–guest interactions, profit from systematic investigations of an idealized model by advanced analytical techniques and simulations. The review describes an integrated approach targeting the deliberate design of pillared layer metal–organic frameworks as idealized model materials for the analysis of critical factors affecting framework dynamics and summarizes the resulting progress in their understanding and application. Flexible Metal‐Organic Frameworks respond to molecular or physical stimuli with spontaneous pore opening or closing, leading to applications in gas separation, storage, sensing, actuation etc. The review provides insights into decisive factors affecting switchability gained from combined simulations, in situ characterization methods and the dedicated design of pillared‐layer MOF model materials varying in composition, structure, size, morphology, and disorder.