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1. Membrane-supported metal organic framework based nanopacked bed for protection against toxic vapors and gases

   https://doi.org/https://doi.org/10.1016/j.seppur.2020.117406  

   Song, Yufeng ; Chau, John ; Sirkar, Kamalesh K. ; Peterson, Gregory W. ; Beuscher, Uwe ( July 2020 , Separation and purification technology)

   null (Ed.)

   Defense against small molecule toxic gases is an important aspect of protection against chemical and biological threat as well as chemical releases from industrial accidents. Current protective respirators/garments cannot effectively block small molecule toxic gases and vapors and retain moisture transmission capability without a heavy burden. Here, we developed a nanopacked bed of nanoparticles of UiO-66-NH₂ metal organic framework (MOF) by synthesizing them in the pores of microporous expanded polytetrafluoroethylene (ePTFE) membranes. The submicron scale size of membrane pores ensures a large surface area of MOF nanoparticles which can capture/adsorb and react with toxic gas molecules efficiently. It was demonstrated that the microporous ePTFE membrane with UiO-66-NH₂ MOF grown inside and around the membrane can defend against ammonia for a significant length of time while allowing passage of moisture and nitrogen. It was also demonstrated that the MOF-loaded ePTFE membrane could provide significant protection from Cl₂ intrusion as well as intrusion from 2-chloroethyl ethyl sulfide (CEES) (a simulant for sulfur mustard). Such MOF-filled membranes exhausted by NH₃ breakthrough experiments were regenerated conveniently by heating at 60 °C for one week under vacuum for further/repeated use; a single regenerated membrane could block NH₃ for 200–300 min. The moisture permeability of such a membrane/nanopacked bed was considerably above the breathability threshold value of 2000 g/m² -day. The results suggest that microporous membranes filled with reactive MOF nanoparticles could be designed as protective barriers against toxic gases/vapors, e.g., NH₃ and Cl₂ and yet be substantially permeable to H₂O and air. 

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2. Identifying UiO‐67 Metal‐Organic Framework Defects and Binding Sites through Ammonia Adsorption

   https://doi.org/10.1002/cssc.202102217  

   Swaroopa Datta Devulapalli, Venkata ; McDonnell, Ryan P. ; Ruffley, Jonathan P. ; Shukla, Priyanka B. ; Luo, Tian‐Yi ; De Souza, Mattheus L. ; Das, Prasenjit ; Rosi, Nathaniel L. ; Karl Johnson, J. ; Borguet, Eric ( December 2021 , ChemSusChem)

   Ammonia is a widely used toxic industrial chemical that can cause severe respiratory ailments. Therefore, understanding and developing materials for its efficient capture and controlled release is necessary. One such class of materials is 3D porous metal‐organic frameworks (MOFs) with exceptional surface areas and robust structures, ideal for gas storage/transport applications. Herein, interactions between ammonia and UiO‐67‐X (X: H, NH₂, CH₃) zirconium MOFs were studied under cryogenic, ultrahigh vacuum (UHV) conditions using temperature‐programmed desorption mass spectrometry (TPD‐MS) and in‐situ temperature‐programmed infrared (TP‐IR) spectroscopy. Ammonia was observed to interact with μ₃−OH groups present on the secondary building unit of UiO‐67‐X MOFs via hydrogen bonding. TP‐IR studies revealed that under cryogenic UHV conditions, UiO‐67‐X MOFs are stable towards ammonia sorption. Interestingly, an increase in the intensity of the C−H stretching mode of the MOF linkers was detected upon ammonia exposure, attributed to NH−π interactions with linkers. These same binding interactions were observed in grand canonical Monte Carlo simulations. Based on TPD‐MS, binding strength of ammonia to three MOFs was determined to be approximately 60 kJ mol⁻¹, suggesting physisorption of ammonia to UiO‐67‐X. In addition, missing linker defect sites, consisting of H₂O coordinated to Zr⁴⁺sites, were detected through the formation ofnNH₃⋅H₂O clusters, characterized through in‐situ IR spectroscopy. Structures consistent with these assignments were identified through density functional theory calculations. Tracking these bands through adsorption on thermally activated MOFs gave insight into the dehydroxylation process of UiO‐67 MOFs. This highlights an advantage of using NH₃for the structural analysis of MOFs and developing an understanding of interactions between ammonia and UiO‐67‐X zirconium MOFs, while also providing directions for the development of stable materials for efficient toxic gas sorption.

    

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3. 1-Alkyl-3-Methylimidazolium Cation Binding Preferences in Hexafluorophosphate Ionic Liquid Clusters Determined Using Competitive TCID Measurements and Theoretical Calculations

   https://doi.org/10.1039/D1CP02928B  

   Roy, Harrison A. ; Rodgers, Mary ( January 2021 , Physical Chemistry Chemical Physics)

   null (Ed.)

   Ionic liquids (ILs) exhibit unique properties that have led to their development and widespread use for a variety of applications. Development efforts have generally focused on achieving desired macroscopic properties via tuning of the IL through variation of the cations and anions. Both the macroscopic and microscopic properties of an IL influence its tunability and thus feasibility of use for selected applications. Works geared toward a microscopic understanding of the nature and strength of the intrinsic cation-anion interactions of ILs have been limited to date. Specifically, the intrinsic strength of the cation-anion interactions in ILs is largely unknown. In previous work, we employed threshold collision-induced dissociation (TCID) approaches supported and enhanced by electronic structure calculations to determine the bond dissociation energies (BDEs) and characterize the nature of the cation-anion interactions in a series of four 2:1 clusters of 1-alkyl-3-methylimidazolium cations with the hexafluorophosphate anion, [2C n mim:PF 6 ] + . To examine the effects of the 1-alkyl chain on the structure and energetics of binding, the cation was varied over the series: 1-ethyl-3-methylimidazolium, [C 2 mim] + , 1-butyl-3-methylimidazolium, [C 4 mim] + , 1-hexyl-3-methylimidazolium, [C 6 mim] + , and 1-octyl-3-methylimidazolium, [C 8 mim] + . The variation in the strength of binding among these [2C n mim:PF 6 ] + clusters was found to be similar in magnitude to the average experimental uncertainty in the measurements. To definitively establish an absolute order of binding among these [2C n mim:PF 6 ] + clusters, we extend this work again using TCID and electronic structure theory approaches to include competitive binding studies of three mixed 2:1 clusters of 1-alkyl-3-methylimidazolium cations and the hexafluorophosphate anion, [C n-2 mim:PF 6 :C n mim] + for n = 4, 6, and 8. The absolute BDEs of these mixed [C n-2 mim:PF 6 :C n mim] + clusters as well as the absolute difference in the strength of the intrinsic binding interactions as a function of the cation are determined with significantly improved precision. By combining the thermochemical results of the previous independent and present competitive measurements, the BDEs of the [2C n mim:PF 6 ] + clusters are both more accurately and more precisely determined. Comparisons are made to results for the analogous [2C n mim:BF 4 ] + and [C n-2 mim:PF 6 :C n mim] + clusters previously examined to elucidate the effects of the [PF 6 ] - and [BF 4 ] - anions on the binding. 

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4. Small Molecule Activation with Intramolecular “Inverse” Frustrated Lewis Pairs

   https://doi.org/10.1002/chem.202005143  

   Manankandayalage, Chamila ; Unruh, Daniel K. ; Krempner, Clemens ( March 2021 , Chemistry – A European Journal)

   The intramolecular “inverse” frustrated Lewis pairs (FLPs) of general formula 1‐BR₂‐2‐[(Me₂N)₂C=N]‐C₆H₄(3–6) [BR₂=BMes₂(3), BC₁₂H₈, (4), BBN (5), BBNO (6)] were synthesized and structurally characterized by multinuclear NMR spectroscopy and X‐ray analysis. These novel types of pre‐organized FLPs, featuring strongly basic guanidino units rigidly linked to weakly Lewis acidic boryl moieties via anortho‐phenylene linker, are capable of activating H−H, C−H, N−H, O−H, Si−H, B−H and C=O bonds.4and5deprotonated terminal alkynes and acetylene to form the zwitterionic borates 1‐(RC≡C‐BR₂)‐2‐[(Me₂N)₂C=NH]‐C₆H₄(R=Ph, H) and reacted with ammonia, BnNH₂and pyrrolidine, to generate the FLP adducts 1‐(R₂HN→BR₂)‐2‐[(Me₂N)₂C=NH]‐C₆H₄, where the N‐H functionality is activated by intramolecular H‐bond interactions. In addition,5was found to rapidly add across the double bond of H₂CO, PhCHO and PhNCO to form cyclic zwitterionic guanidinium borates in excellent yields. Likewise,5is capable of cleaving H₂, HBPin and PhSiH₃to form various amino boranes. Collectively, the results demonstrate that these new types of intramolecular FLPs featuring weakly Lewis acidic boryl and strongly basic guanidino moieties are as potent as conventional intramolecular FLPs with strongly Lewis acidic units in activating small molecules.

    

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5. Synthesis, structures, and reactivity of isomers of [RuCp*(1,4-(Me 2 N) 2 C 6 H 4 )] 2

   https://doi.org/10.1039/D1DT02155A  

   Longhi, Elena ; Risko, Chad ; Bacsa, John ; Khrustalev, Victor ; Rigin, Sergei ; Moudgil, Karttikay ; Timofeeva, Tatiana V. ; Marder, Seth R. ; Barlow, Stephen ( September 2021 , Dalton Transactions)

   [RuCp*(1,3,5-R 3 C 6 H 3 )] 2 {Cp* = η 5 -pentamethylcyclopentadienyl, R = Me, Et} have previously been found to be moderately air stable, yet highly reducing, with estimated D + /0.5D 2 (where D 2 and D + represent the dimer and the corresponding monomeric cation, respectively) redox potentials of ca. −2.0 V vs. FeCp 2 +/0 . These properties have led to their use as n-dopants for organic semiconductors. Use of arenes substituted with π-electron donors is anticipated to lead to even more strongly reducing dimers. [RuCp*(1-(Me 2 N)-3,5-Me 2 C 6 H 3 )] + PF 6 − and [RuCp*(1,4-(Me 2 N) 2 C 6 H 4 )] + PF 6 − have been synthesized and electrochemically and crystallographically characterized; both exhibit D + /D potentials slightly more cathodic than [RuCp*(1,3,5-R 3 C 6 H 3 )] + . Reduction of [RuCp*(1,4-(Me 2 N) 2 C 6 H 4 )] + PF 6 − using silica-supported sodium–potassium alloy leads to a mixture of isomers of [RuCp*(1,4-(Me 2 N) 2 C 6 H 4 )] 2 , two of which have been crystallographically characterized. One of these isomers has a similar molecular structure to [RuCp*(1,3,5-Et 3 C 6 H 3 )] 2 ; the central C–C bond is exo , exo , i.e. , on the opposite face of both six-membered rings from the metals. A D + /0.5D 2 potential of −2.4 V is estimated for this exo , exo dimer, more reducing than that of [RuCp*(1,3,5-R 3 C 6 H 3 )] 2 (−2.0 V). This isomer reacts much more rapidly with both air and electron acceptors than [RuCp*(1,3,5-R 3 C 6 H 3 )] 2 due to a much more cathodic D 2 ˙ + /D 2 potential. The other isomer to be crystallographically characterized, along with a third isomer, are both dimerized in an exo , endo fashion, representing the first examples of such dimers. Density functional theory calculations and reactivity studies indicate that the central bonds of these two isomers are weaker than those of the exo , exo isomer, or of [RuCp*(1,3,5-R 3 C 6 H 3 )] 2 , leading to estimated D + /0.5D 2 potentials of −2.5 and −2.6 V vs. FeCp 2 +/0 . At the same time the D 2 ˙ + /D 2 potentials for the exo , endo dimers are anodically shifted relative to those of [RuCp*(1,3,5-R 3 C 6 H 3 )] 2 , resulting in much greater air stability than for the exo , exo isomer. 

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