Precise Modulation of the Breathing Behavior and Pore Surface in Zr‐MOFs by Reversible Post‐Synthetic Variable‐Spacer Installation to Fine‐Tune the Expansion Magnitude and Sorption Properties

Abstract

To combine flexibility and modifiability towards a more controllable complexity of MOFs, a post-synthetic variable-spacer installation (PVSI) strategy is used to implement kinetic installation/ uninstallation of secondary ligands into/from a robust yet flexible proto-Zr-MOF. This PVSI process features precise positioning of spacers with different length, size, number, and functionality, enabling accurate fixation of successive breathing stages and fine-tuning of pore surface. It shows unprecedented synthetic tailorability to create complicated MOFs in a predictable way for property modification, for example, CO2 and R22 adsorption/separation, thermal/chemical stability, and extended breathing behavior.

Retrofitting metal-organic frameworks

“…In the most general definition, retrofitting of a MOF describes the post-synthetic installation of additional linkers between undercoordinated metal nodes or between open metal sites (OMSs) of a MOF 21 . Subsequently, retrofitting has been discovered as a powerful approach to manipulate macroscopic physicochemical properties such as the mechanical robustness, the thermal expansion behavior and responsivity of flexible MOFs to guest adsorption 21–23 . In a typical retrofitting experiment, a MOF with guest accessible OMSs or labile monotopic ligands is exposed to a molecule with at least two available coordination sites such as nitrile or carboxylate groups.…”

Thermochromic Behavior of Azobenzene‐based Coordination Polymer with Reversible Breathing Process

“…Stimuli‐responsive materials have aroused intense interest due to their potential applications in molecular devices (such as chemical switches, sensors, and memory devices) . They can tune their physical properties with the external stimulation, for instance, pressure, temperature, pH, light or X‐ray and electric/magnetic field.…”

Unusual adsorption behaviours and responsive structural dynamics via selective gate effects of an hourglass porous metal–organic framework

“…On the other hand, it has been found that some unique properties, like extraordinary gas adsorption/separation behaviors, can be obtained via internal structural dynamics. For example, gateopening [14][15][16] and breathing [17][18][19][20] behaviors are important known phenomena, occurring through reversible structural transitions between two or more states triggered via pressure or temperature variations or guest binding, providing a unique approach to develop multifunctional porous materials. 21,22 The dynamic behaviors of MOFs in response to external stimuli, can be triggered by several mechanisms, such as sliding of interlocked fragments of interpenetrated frameworks, 23,24 coordination geometry rearrangements of metal centers or clusters, [25][26][27] rotational motion involving exible parts of bridging ligands, 16,[28][29][30][31][32][33] or a combined mechanism containing more than one of the above three.…”

“…Since interpenetration oen leads to a shrink of solvent accessible volume, [34][35][36] we pay more attention to the geometry rearrangement of the coordination environment and to the bond rotation of organic linkers. 20,[37][38][39][40][41] If the framework exibility and dynamics are generated by the bond rotation, it usually neither changes the topology of the whole framework nor dramatically reduces porosity. Moreover, it can temporarily open the narrow apertures of the coordination framework to facilitate kinetic diffusion of guest molecules and/or accept oversized guest molecules to give stepwise sorption behavior, [42][43][44] thus providing specic applications for gas separation, bio-chemical sensing, etc.…”