Large breathing effect in ZIF-65(Zn) with expansion and contraction of the SOD cage

Abstract

The flexibility and guest-responsive behavior of some metal-organic frameworks (MOFs) indicate their potential in the fields of sensors and molecular recognition. As a subfamily of MOFs, the flexible zeolitic imidazolate frameworks (ZIFs) typically feature a small displacive transition due to the rigid zeolite topology. Herein, an atypical reversible displacive transition (6.4 Å) is observed for the sodalite (SOD) cage in flexible ZIF-65(Zn), which represents an unusually large breathing effect compared to other ZIFs. ZIF-65(Zn) exhibits a stepwise II → III → I expansion between an unusual ellipsoidal SOD cage (8.6 Å × 15.9 Å for II) and a spherical SOD cage (15.0 Å for I). The breathing behavior of ZIF-65(Zn) varies depending on the nature of the guest molecules (polarity and shape). Computational simulations are employed to rationalize the differences in the breathing behavior depending on the structure of the ZIF-65(Zn) cage and the nature of the guest-associated host–guest and guest–guest interactions.

Functionality-Induced Locking of Zeolitic Imidazolate Frameworks

“…The effects of functionalization on structural flexibility and gas separation were systematically investigated by combining XRD analyses, gas adsorption, and dynamic breakthrough experiments. The functionality-induced locking uncovered here fundamentally differs from the linker swing dynamics 16−19 and flexible deformation 21 previously observed in ZIFs. A rigid porous structure maximizes the linker−linker interaction through irreversible structural transformation upon thermal treatment.…”

“…16−19 Although significant structural transformation due to this linker swinging motion has rarely been investigated, recently, reversible structure transformation was studied during guest removal and adaptive inclusion of guest molecules in zeolite SOD ZIF-65, which exhibited a large amplitude of distortion in its SOD cages. 20,21 Herein, we uncover functionality-induced locking in ZIFs that leads to an irreversible structural transformation, highlighted by a significant contraction of their unit cells upon thermal activation to rigidify the framework. This finding conceptually advances the importance of functionality-induced locking via framework flexibility by a maximal linker−linker interaction.…”

“…As a subclass of metal–organic frameworks (MOFs), , zeolitic imidazolate frameworks (ZIFs) are constructed by stitching tetrahedral metal centers (M = Co II , Zn II , Cd II , and Li I /B III , among others) − together using imidazolate and its functionalized derivatives to form tetrahedral networks resembling those structural types observed or even unrealized in inorganic zeolites. − Featuring exceptional chemical stabilities and accessible microporosity, ZIFs have attracted considerable attention for use in carbon capture and industrial gas separations, given their pronounced architectural rigidity and ease of functionalization. − However, the imidazolate linkers used to construct ZIFs are usually dynamic via swinging motions, which imposes inherent framework flexibility during gas adsorption. − This phenomenon directly impacts ZIFs’ performance in practical gas separation processes, especially at higher gas pressures. Ingenious strategies have been proposed in membrane separation processes to suppress the swinging motion of linkers by introducing external stimuli that lead to enhanced separation performance, − but such strategies remain underdeveloped in the practice of adsorptive gas separation processes, such as pressure swing adsorption (PSA).…”

Ion-transporting channel-embedded MOF-in-COF structures as composite quasi-solid electrolytes with highly enhanced electrochemical properties

“…This expansion may result from distortions in the ZIF-8-unit cell caused by repulsive interactions between the COF and imidazole groups in ZIF-8. 43 Furthermore, the pore structure of the TpPa COF is maintained in the MC film, with a decrease in intensity. This decrease can be explained by the confinement of ZIF-8 within the pores, which become filled.…”

Polynuclear Rare-Earth Cluster-Directed Self-Assembly of Highly Porous Zeolite-like Metal–Organic Frameworks with Methane Storage Property

“…Zeolite-like metal–organic frameworks (ZMOFs), a subset of metal–organic frameworks, have attracted great scientific attention given their unique pore system, distinctive cage-like cavities, and various applications. − Generally, there are three avenues to access the deliberate construction of ZMOFs. First, the combinations of single-metal ions with functionalized imidazole or imidazole derivatives, − which demonstrates plentiful known/unknown zeolitic topologies along with limited porosities for gas storage under high pressure and structural flexibility detrimental to gas separation. − Second, the utilization of corner-sharing supertetrahedra building blocks constructed from trinuclear metal clusters with di/tricarboxylates, which exhibits merely mtn topology. − Third, the combinations of tetrahedral inorganic clusters/organic linkers with linear linkers/tetrahedral metal ions or clusters, − which results in a few types of ZMOFs suffering from stability and porosity issues. Hence, controllable synthesis of new types of ZMOFs is highly desirable but remains a great challenge.…”