Frustrated Flexibility in Metal-Organic Frameworks

Abstract

<div><div><div><p>Stimuli-responsive flexible metal-organic frameworks (MOFs) remain at the forefront of porous materials research due to their enormous potential for various technological applications. Here, we introduce the concept of frustrated flexibility in MOFs, which arises from an incompatibility of intra-framework dispersion forces with the geometrical constraints of the inorganic building units. Controlled by appropriate linker functionalization with dispersion energy donating alkoxy groups, this approach results in a series of MOFs exhibiting a new type of guest- and temperature-responsive structural flexibility characterized by reversible loss and recovery of crystalline order under full retention of framework connectivity and topology. The stimuli-dependent phase change of the frustrated MOFs involves non-correlated deformations of their inorganic building unit, as probed by a combination of global and local structure techniques together with computer simulations. Frustrated flexibility may be a common phenomenon in MOF structures, which are commonly regarded as rigid, and thus may be of crucial importance for the performance of these materials in various applications.</p></div></div></div>

Guest-mediated phase transitions in a flexible pillared-layered metal–organic framework under high-pressure

“…Flexible metal-organic frameworks (MOFs) may undergo dynamic and reversible structural changes under external stimuli, such as applied pressure or adsorption/desorption of guest. [1][2][3][4][5] Structural flexibility is inherited from deformable metal coordination centres, conformational or rotational freedom of the organic linkers, structural defects, or flexible network topologies. Pronounced structural deformation may occur with retention of the framework crystallinity, allowing structural changes to be followed by in situ single crystal X-ray diffraction.…”

CO2 and Temperature Induced Switching of a Flexible Metal-Organic Framework with Surface-Mounted Nanoparticles

“…For electric-field induced phase transitions only a few reports exists, 24,25 while temperature and mechanical pressure have shown to be suitable stimuli for switching between the np and lp form in materials such as ZIF-4, MIL-53 and its derivates, and members of the series [M(fu-bdc)2dabco]. 3,26,27 Additionally, studies on systems such as linker-functionalized MOF-5 derivates 28 and [Cu(DB-bdc)2dabco] 29 have highlighted the complex interplay between enthalpic and entropic interactions that cause trigger-induced structural flexibility. Here, we would like to highlight the contribution of several theoretical studies on this topic, which, in synergy with experimental works, helped to step-wise carve out a clearer picture of the structure-chemical factors that determine flexibility in MOFs.…”