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.

The synthesis and structural flexibility of the metal–organic frameworks M₂(2,6-ndc)₂(dabco) (DUT-8(M), M = Ni, Co, Cu, Zn; 2,6-ndc = 2,6-naphthalenedicarboxylate, dabco = 1,4-diazabicyclo[2.2.2]octane) as well as their characterization by gas adsorption, ¹²⁹Xe NMR and ¹³C MAS NMR spectroscopy are described. Depending on the integrated metal atom the compounds show reversible (DUT-8(Ni), DUT-8(Co)), non-reversible (DUT-8(Zn)) or no (DUT-8(Cu)) structural transformation upon solvent removal and/or physisorption of several gases. DUT-8(Co) exhibits a similar structural transformation by solvent removal and adsorption behavior as observed for DUT-8(Ni). DUT-8(Zn) undergoes an irreversible structural change caused by solvent removal. The non-flexible copper containing MOF reveals the best performance concerning porosity and gas storage capacities within the DUT-8 series. Xenon adsorption studies combined with ¹²⁹Xe NMR spectroscopy are used to study the flexibility of the DUT-8 compounds. ¹²⁹Xe chemical shift and line width strongly depend on the metal atom. Solid-state ¹³C NMR spectroscopy has been applied in order to further characterize the organic parts of the DUT-8 frameworks. While DUT-8(Ni) exhibits narrow, well-resolved lines in its “as made” state, the signals of DUT-8(Co) are broadened and shifted over an unusually wide chemical shift range (−72 to 717 ppm). No detectable signals are found in DUT-8(Cu) indicating significantly changed internal dynamics compared to DUT-8(Ni) and DUT-8(Co).

Nuclear Magnetic Resonance (NMR) spectroscopy is a well-established method for the investigation of various types of porous materials. During the past decade, metal–organic frameworks have attracted increasing research interest. Solid-state NMR spectroscopy has rapidly evolved into an important tool for the study of the structure, dynamics and flexibility of these materials, as well as for the characterization of host–guest interactions with adsorbed species such as xenon, carbon dioxide, water, and many others. The present review introduces and highlights recent developments in this rapidly growing field.