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We present a newly developed instrument for 22Na-based positron-annihilation lifetime spectroscopy, designed to facilitate the simultaneous control of temperature, gas atmosphere, and humidity in a single experimental system. The spectrometer operates within a temperature range of 50–480 K and pressures from 10−6 mbar to 1.5 bars. It features a novel gas dosing chamber that allows in situ adsorption studies with gases such as but not limited to CO2, N2, Ar, O2, and their mixtures, with precise control over mixing ratios. Additionally, the device supports in situ humidity exposure, allowing for comprehensive studies of sample interactions with both humidity and humid gases. Fully automated, the system provides seamless data acquisition and environmental control, including pressure and temperature regulation. We demonstrate the instrument's capability to elucidate alterations in the free volume of maltodextrin under humidity exposure. Additionally, we illustrate the instrument's efficacy through case studies on CPO-27 metal-organic frameworks (MOFs), highlighting its versatility in analyzing adsorption phenomena across diverse gas adsorbates and temperatures. This state-of-the-art spectrometer stands as an indispensable tool for probing the physicochemical attributes of materials under varying conditions, providing pivotal insights into gas adsorption mechanisms and material dynamics. [ABSTRACT FROM AUTHOR]

Stimuli‐responsive physisorbents that undergo reversible structural transformations induced by external stimuli (e.g. light, guests, or heat) offer the promise of utility in gas storage and separation. Whereas reports on guest or light‐responsive sorbents have increased in recent years, we are unaware of reports on sorbents that exhibit both light and guest‐induced structural transformations. Herein, we report that the square lattice, sql, topology coordination network Zn(fba)(bis) ⋅ 2DMF (sql‐5,6‐Zn‐α, 5=trans‐4,4′‐bis(1‐imidazolyl)stilbene=bis, 6=2,2‐bis(4‐carboxyphenyl)hexafluoropropane=H2fba) underwent single‐crystal‐to‐single‐crystal transformation (SCSC) upon activation, affording nonporous sql‐5,6‐Zn‐β. Parallel alignment at 3.23 Å of olefinic moieties on adjacent bis ligands in sql‐5,6‐Zn‐α enabled SCSC [2+2] photocycloaddition upon exposure to UV light (365 nm) or sunlight. sql‐5,6‐Zn‐α thereby transformed to mot‐5,6‐Zn‐α, which was subsequently activated to the narrow pore phase mot‐5,6‐Zn‐β. sql‐5,6‐Zn‐β and mot‐5,6‐Zn‐β both exhibited S‐shaped adsorption isotherms characteristic of guest‐induced structural changes when exposed to CO2 at 195 K (type‐F–IV and type F–I, respectively). Cycling experiments conducted upon sql‐5,6‐Zn‐β reduced particle size after cycle 1 and induced transformation into a rare example of a shape memory coordination network, sql‐5,6‐Zn‐γ. Insight into this smorgasbord of SCSC phase changes was gained from in situ PXRD, single crystal XRD and 1H NMR spectroscopy experiments. [ABSTRACT FROM AUTHOR]

The approach of employing multivariate MOFs was used to fine-tune the mechanical properties of the flexible framework DUT-49. In situ XRD, NMR and physisorption studies showed that the partial incorporation of a more rigid linker into the DUT-49 framework enables stabilization of the metastable open pore phase, which led to a two-fold amplification of the expelled gas amount upon the "negative gas adsorption" transition. [ABSTRACT FROM AUTHOR]

Crystal size engineering allows tailoring of flexible metal–organic frameworks (MOFs) to achieve new properties. The gating type flexibility of the DUT-8(Zn) ([Zn2(2,6-ndc)2(dabco)]n, 2,6-ndc = 2,6-naphthalene dicarboxylate, dabco = 1,4-diazabicyclo-[2.2.2]-octane) compound is known to be extremely particle size sensitive. Here, the physisorption of ethanol vapor gives rise to so-called shape-memory effect, leading to rigidification and flexibility suppression. According to powder X-ray diffraction and nitrogen physisorption experiments, the open pore phase is retained selectively after desorption of alcohols, which could be attributed to the nano-structuring and surface deformation of the crystals as a result of exposure to alcohols. [ABSTRACT FROM AUTHOR]

Metal‐Organic Frameworks can be grafted with amines by coordination to metal vacancies to create amine‐appended solid adsorbents, which are being considered as an alternative to using aqueous amine solutions for CO2 capture. In this study, we propose an alternative mechanism that does not rely on the use of neutral metal vacancies as binding sites but is enabled by the structural adaptability of heterobimetallic Ti2Ca2 clusters. The combination of hard (Ti4+) and soft (Ca2+) metal centers in the inorganic nodes of the framework enables MUV‐10 to adapt its pore windows to the presence of triethylenetetramine molecules. This dynamic cluster response facilitates the translocation and binding of tetraamine inside the microporous cavities to enable the formation of bis‐coordinate adducts that are stable in water. The extension of this grafting concept from MUV‐10 to larger cavities not restrictive to CO2 diffusion will complement other strategies available for the design of molecular sorbents for decarbonization applications. [ABSTRACT FROM AUTHOR]

Understanding and control of the spatiotemporal stimuli-responsiveness of flexible metal–organic frameworks are crucial for the development of novel adsorbents for gas storage and separation technologies. Herein, we report two isostructural pillared-layer dynamic frameworks differing only in one atom that bridge a benzenocarboxylate linker. Through a synthetic approach, we switch the stepwise CO2-induced transformation into a continuous one. Our findings are proved by equilibrium and time-resolved in situ powder X-ray diffraction collected during CO2 adsorption at 195 K. Finally, we use high-pressure single and multi-gas adsorption experiments to show the superiority of continuous breathing in CH4 storage and CH4/CO2 separation at 298 K. This report demonstrates that the desirable mechanism of flexible frameworks can be readily achieved through single-atom exchange enabling efficient gas separation and storage. [ABSTRACT FROM AUTHOR]