Metal-organic frameworks (MOFs), with their high porosities and surface areas, show great utility in the field of gas adsorption. To unlock this porosity, MOFs are generally fully activated by removing all adsorbed guests using high temperatures and low pressures. However, this is energy intensive and can be unfeasible if the MOF is part of a composite, where the maximum temperature of the composite is below the activation temperature. To investigate the effect of activation temperature on adsorption, a series of in situ single-crystal X-ray diffraction (scXRD) studies were performed on Ni-MOF-74 loaded with the gas nitric oxide (NO) under different conditions. These experiments uncovered anomalous adsorption results where partially activated samples adsorb ∼14% more NO per framework material than did the fully activated sample. The scXRD experiments revealed a new NO binding site that is only present if the open metal sites are partially occupied by water molecules. To shed more light on the respective binding of the two different NO sites in Ni-MOF-74, these were studied in situ under different treatment conditions, such as the exposure to vacuum at different temperatures. This study yields insights into the nature of binding sites in MOFs, how these are affected by activation, and helps to pave the way for the improved design of processing conditions.

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The fascinating feature of metal-organic frameworks is that they can respond to external stimuli, unlike other inorganic materials. This feature corresponds to the framework's flexibility, which originates with the long-range crystalline order of the framework accompanied by cooperative structural transformability. We have synthesized a novel metal-organic framework comprised of Cu(I) nodes with pyrazine linkers and benzene-1,3,5-tricarboxylate acting as template anions, named CUCAM-1 [Cu(Py)2(BTC)]n. In the presence of polar solvent systems, CUCAM-1 undergoes an irreversible structural transformation to yield a mixed phase that consists of HKUST-1 [Cu3(BTC)2(H2O)3]n and another CUCAM-2 [Cu(Py)(BTC)]n MOFs, whose novel structure is successfully revealed by continuous rotation electron diffraction from the mixture. In this structural transformation, a new ligand exchange occurs where template anions become ligands, confirmed by single crystal X-ray analysis. Further, structural transformation and the mechanism are explained by ab initio molecular dynamics (AIMD) simulations. Interestingly, different halides (F-, Cl-, and Br-) can be accompanied to affect/control the composition of the second phase by favoring the formation of the HKUST-1 phase over CUCAM-2, which was evident by the powder X-ray diffraction studies. Furthermore, the structural transformation induced by I- resulted in a colorimetric response due to the formation of a new MOF CUCAM-3, paving the way for use as an iodide detector.

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A series of four novel microporous alkaline earth metal-organic frameworks (AE-MOFs) containing methanetetrabenzoate linker (MTB) with composition {[Ca4(μ8-MTB)2]·2DMF·4H2O} n (UPJS-6), {[Ca4(μ4-O)(μ8-MTB)3/2(H2O)4]·4DMF·4H2O} n (UPJS-7), {[Sr3(μ7-MTB)3/2]·4DMF·7H2O} n (UPJS-8) and {[Ba3(μ7-MTB)3/2(H2O)6]·2DMF·4H2O} n (UPJS-9) (UPJS = University of Pavol Jozef Safarik) have been successfully prepared and characterized. The framework stability and thermal robustness of prepared materials were investigated using thermogravimetric analysis (TGA) and high-energy powder X-ray diffraction (HE-PXRD). MOFs were tested as adsorbents for different gases at various pressures and temperatures. Nitrogen and argon adsorption showed that the activated samples have moderate BET surface areas: 103 m2 g-1 (N2)/126 m2 g-1 (Ar) for UPJS-7'', 320 m2 g-1 (N2)/358 m2 g-1 (Ar) for UPJS-9'' and UPJS-8'' adsorbs only a limited amount of N2 and Ar. It should be noted that all prepared compounds adsorb carbon dioxide with storage capacities ranging from 3.9 to 2.4 wt% at 20 °C and 1 atm, and 16.4-13.5 wt% at 30 °C and 20 bar. Methane adsorption isotherms show no adsorption at low pressures and with increasing pressure the storage capacity increases to 4.0-2.9 wt% of CH4 at 30 °C and 20 bar. Compounds displayed the highest hydrogen uptake of 3.7-1.8 wt% at -196 °C and 800 Torr among MTB containing MOFs.

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