Direct Structural Identification of Gas Induced Gate‐Opening Coupled with Commensurate Adsorption in a Microporous Metal–Organic Framework

Gate‐opening is a unique and interesting phenomenon commonly observed in flexible porous frameworks, where the pore characteristics and/or crystal structures change in response to external stimuli such as adding or removing guest molecules. For gate‐opening that is induced by gas adsorption, the pore‐opening pressure often varies for different adsorbate molecules and, thus, can be applied to selectively separate a gas mixture. The detailed understanding of this phenomenon is of fundamental importance to the design of industrially applicable gas‐selective sorbents, which remains under investigated due to the lack of direct structural evidence for such systems. We report a mechanistic study of gas‐induced gate‐opening process of a microporous metal–organic framework, [Mn(ina)₂] (ina=isonicotinate) associated with commensurate adsorption, by a combination of several analytical techniques including single crystal X‐ray diffraction, in situ powder X‐ray diffraction coupled with differential scanning calorimetry (XRD‐DSC), and gas adsorption–desorption methods. Our study reveals that the pronounced and reversible gate opening/closing phenomena observed in [Mn(ina)₂] are coupled with a structural transition that involves rotation of the organic linker molecules as a result of interaction of the framework with adsorbed gas molecules including carbon dioxide and propane. The onset pressure to open the gate correlates with the extent of such interaction.     

Metal Bromide Controlled Interfacial Aromatization Reaction for Shape‐Selective Synthesis of Palladium Nanostructures with Efficient Catalytic Performances

Herein, the effect of diverse metal bromides for the shape evolution of palladium nanostructures (Pd NS) has been demonstrated. Aromaticity‐driven reduction of bromopalladate(II) is optimized to reproducibly obtain different Pd NS at the water/organic layer interface. In this soft interfacial strategy, a redox potential driven reaction has been performed, forming the thermodynamically more stable (>10⁴‐fold) PdBr₄^2? precursor from PdCl₄^2? by adding extra metal bromides. In the process, the reductant, Hantzsch dihydropyridine ester (DHPE), is aromatized. Interestingly, alkali metal bromides devoid of coordination propensity exclusively evolve Pd nanowires (Pd NWs), whereas in the case of transition metal bromides the metal ions engage the ‘N’ donor of DHPE at the interface, making the redox reaction sluggish. Hence, controlled Pd nanoparticles growth is observed, which evolves Pd broccolis (Pd NBRs) and Pd nanorods (Pd NRs) at the interface in the presence of NiBr₂ and CuBr₂, respectively, in the aqueous solution. Thus, the effect of diverse metal bromides in the reaction mixture for tailor‐made growth of the various Pd NS is reported. Among the as‐synthesized materials, the Pd NWs stand to be superior catalysts and their efficiency is almost 6 and 2.5 times higher than commercial 20 % Pd/C in the electrooxidation of ethanol and Cr^VI reduction reaction by formic acid, respectively.     

Photopolymerization of methyl methacrylate with the use of iodine monobromide as photoinitiator

Iodine monobromide easily induces photopolymerization of methyl methacrylate (MMA) at 40°C under visible light. Initiator exponent and monomer exponent values were found to be 0.5 and 2, respectively, at low initiator concentrations, while the corresponding values at high initiator concentration conditions were zero and 3. The chain transfer constant of IBr at 40°C was found to be 13.0. Kinetic and other data indicate a radical polymerization mechanism involving complexation of monomer molecules with iodine monobromide prior to radical generation, and termination is believed to take place biomolecularly at low IBr concentrations and unimolecularly, involving reaction with the initiator, at high IBr concentrations (initiator termination).     

Thermoanalytical study of the solid state reaction between hydrated ZnO and Fe2O3

The hydrated oxides which are formed by the addition of ammonium bi-carbonate to a solution of Zn(NO₃)₂ and Fe(NO₃)₃, and drying the precipitates at 110° are zinc hydroxy carbonate(I) and iron(III) oxide gel(II), respectively. A new, derived derivative thermogravimetric curve along with conventional DTA and DTG methods have been used to study the reaction between (I) and (II) in two components system.A mixture of (I) and (II) subjected to grinding yields about 16% zinc ferrite precursor. In a sample prepared by coprecipitation from the mixed nitrate solution and drying at 110°, nearly 70% precursor is formed. The formation of zinc ferrite spinel reported to take place at low temperature in such cases appears to be related with the formation of the precursor, and reactivity and phase transformation temperature in Fe₂O₃.

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Zusammenfassung Die durch Zugabe von Ammoniumbicarbonat zu einer Lösung von Zn(NO₃)₂ und Fe(NO₃)₃ und Trocknung des Niederschlags bei 110° gebildeten hydratisierten Oxide sind Zinkhydroxycarbonat (I) bzw. Eisen(III)oxidgel (II). Eine neue derivierte derivative thermogravimetrische Kurve wurde gemeinsam mit den konventionellen DTA und DTG Methoden zum Studium der Reaktion zwischen (I) und (II) in Zweikomponentensystemen eingesetzt.Das Gemisch von (I) und (II) ergibt beim Mahlen etwa 16% Zinkferrit »Prekursor«. In einer durch Mitfällung der gemischten Nitrate und Trocknung bei 110° erhaltenen Probe wurde fast 70 % »Prekursor« gebildet. Die Bildung von Zinkferritspinell, über dessen Entstehung in solchen Fällen bei niedrigen Temperaturen berichtet wird, scheint mit der Bildung des »Prekursors« verbunden zu sein, sowie mit der Reaktivität und der Phasenübergangstemperatur in Fe₂O₃.

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Résumé Les oxydes hydratés formés lors de l'addition du bicarbonate d'ammonium à une solution de Zn(NO₃)₂ et de Fe(NO₃)₂ suivie du séchage du précipité à 110°, sont l'hydroxy-carbonate de zinc(I) et le gel de l'oxyde de fer(III) (II). On a utilisé une nouvelle technique de thermogravimétrie en dérivation, ainsi que les méthodes d'ATD et TGD conventionnelles, pour étudier la réaction entre (I) et (II) dans le système à deux composants.Un mélange de (I) et de (II), soumis au broyage, donne environ 16 p.c. de ferrite de zinc «précurseur», tandis qu'un échantillon préparé par coprécipitation à partir de la solution des nitrates mixtes et séchage à 110°, en donne environ 70 p.c.La formation du spinelle de ferrite de zinc décrite comme ayant lieu, dans des cas similaires, à des températures faibles, paraît être en rapport avec la formation du «précurseur» ainsi qu'avec la réactivité et la température de la transformation de phase de Fe₂O₃.

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Zn(NO₃)₂ Fe(NO₃)₃, , 110°, , , (I) (II). , , I II . I II, , 16% , . , 110°, 70% , . « » , Fe₂O₃.

     

Separation of titanium and uranium from other elements by tannin

Summary Titanium and uranium have been precipitated by tannin in the presence of various other ions, e.g., Fe³⁺, Al³⁺, Cr³⁺, Th⁴⁺, Zr⁴⁺, Bi³⁺, Pb²⁺, (VO)²⁺ and rare earths, which are kept in solution by EDTA. The precipitation was carried out by raising the p_H of the acidic solution containing EDTA and tannin by dilute ammonium hydroxide or hexamine. The p_H of complete precipitation of titanium is 4.0 and above and that of uranium is 6.0 and above.

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Zusammenfassung Titan und Uran werden mit Tannin in Gegenwart verschiedener Fremdionen, die durch ÄDTA in Lösung gehalten werden, gefällt (z.B. in Gegenwart von Fe³⁺, Al³⁺, Cr³⁺, Th⁴⁺, Zr⁴⁺, Bi³⁺, Pb²⁺, (VO)²⁺, Seltenen Erden). Die Fällung wird durchgeführt, indem man die saure Lösung, die ÄDTA und Tannin enthält, mit Ammoniak oder Hexamethylentetramin neutralisiert. Titan wird bei p_H-Werten über 4,0 und Uran bei solchen über 6,0 vollständig ausgefällt.

     

Correlations between D and [`(D)]{\overline D} mesons produced in 500 GeV/cπ?-nucleon interactions

We present a study of correlations between D and mesons produced in 500 GeV/cπ⁻-nucleon interactions, based on data from experiment E791 at Fermilab. We have fully reconstructed 791 ± 44 charm meson pairs to study correlations between the transverse and longitudinal momenta of the two D mesons and the relative production rates for different types of D meson pairs. We see slight correlations between the longitudinal momenta of the D and the , and significant correlations between the azimuthal angle of the D and the . The experimental distributions are compared to a next-to-leading-order QCD calculation and to predictions of the PYTHIA/JETSET Monte Carlo event generator. We observe less correlation between transverse momenta and different correlations between longitudinal momenta than these models predict for the default values of the model parameters. Better agreement between data and theory might be achieved by tuning the model parameters or by adding higher order perturbative terms, thus contributing to a better understanding of charm production.The relative production rates for the four sets of charm pairs, as calculated in the PYTHIA/JETSET event generator with the default parameters, agree with data as far as the relative ordering, but predict too many pairs and too few pairs.