Co-catalyst free ethene dimerization over Zr-based metal-organic framework (UiO-67) functionalized with Ni and bipyridine

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Zn Redistribution and Volatility in ZnZrOx Catalysts for CO2 Hydrogenation

ZnO–ZrO2 mixed oxide (ZnZrOx) catalysts are widely studied as selective catalysts for CO2 hydrogenation into methanol at high-temperature conditions (300–350 °C) that are preferred for the subsequent in situ zeolite-catalyzed conversion of methanol into hydrocarbons in a tandem process. Zn, a key ingredient of these mixed oxide catalysts, is known to volatilize from ZnO under high-temperature conditions, but little is known about Zn mobility and volatility in mixed oxides. Here, an array of ex situ and in situ characterization techniques (scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDX), transmission electron microscopy (TEM), powder X-ray diffraction (PXRD), X-ray absorption spectroscopy (XAS), X-ray photoelectron spectroscopy (XPS), Infrared (IR)) was used to reveal that Zn2+ species are mobile between the solid solution phase with ZrO2 and segregated and/or embedded ZnO clusters. Upon reductive heat treatments, partially reversible ZnO cluster growth was observed above 250 °C and eventual Zn evaporation above 550 °C. Extensive Zn evaporation leads to catalyst deactivation and methanol selectivity decline in CO2 hydrogenation. These findings extend the fundamental knowledge of Zn-containing mixed oxide catalysts and are highly relevant for the CO2-to-hydrocarbon process optimization.publishedVersio

Twinning in Zr-Based Metal-Organic Framework Crystals

Ab initio structure determination of new metal-organic framework (MOF) compounds is generally done by single crystal X-ray diffraction, but this technique can yield incorrect crystal structures if crystal twinning is overlooked. Herein, the crystal structures of three Zirconium-based MOFs, that are especially prone to twinning, have been determined from twinned crystals. These twin laws (and others) could potentially occur in many MOFs or related network structures, and the methods and tools described herein to detect and treat twinning could be useful to resolve the structures of affected crystals. Our results highlight the prevalence (and sometimes inevitability) of twinning in certain Zr-MOFs. Of special importance are the works of Howard Flack which, in addition to fundamental advances in crystallography, provide accessible tools for inexperienced crystallographers to take twinning into account in structure elucidation

The Suzuki–Miyaura Cross-Coupling as the Key Step in the Synthesis of 2-Aminobiphenyls and 2,2'-Diaminobiphenyls: Application in the Synthesis of Schiff Base Complexes of Zn

2‐Nitrophenylboronic acids serve as interesting starting materials for the construction of biphenyl‐ and terphenyl‐based amines if subjected to the Suzuki–Miyaura reaction. Unfortunately, these boronic acids suffer from low reactivity in Suzuki reactions, alongside their low stability in the presence of Pd. Herein, a general method for the construction of 2‐nitro‐substituted bi‐ and terphenyls is presented, with special emphasis on the synthesis of 2‐amino‐2'‐nitrobi‐ and terphenyls. Comparisons are made with other boronic acids that have some of the aforementioned issues. Finally, the application of the obtained 2‐amino‐2'‐nitrobi‐ and terphenyls as starting materials for the synthesis of bi‐ and terphenyl based di‐ and triamines is encountered for, with emphasis on the use of these amines as precursors for Schiff base ligands. In addition, the synthesis of some Zn complexes of these ligands is presented

A highly asymmetric gold(III) η3‐allyl complex

A highly asymmetric AuIII η3‐allyl complex has been generated by treating Au(η1‐allyl)Br(tpy) (tpy=2‐(p‐tolyl)pyridine) with AgNTf2. The resulting η3‐allyl complex has been characterized by NMR spectroscopy and X‐ray crystallography. DFT calculations and variable temperature 1H NMR suggest that the allyl ligand is highly fluxional.publishedVersio

NMR spectroscopic investigations into the mechanism of absorption and desorption of CO2 by (tris-pyridyl)amine Zn complexes

The Zn complex [(NN3)Zn(OH)]2(NO3)2 (1(NO3)2, NN3 = tris(2-pyridylmethyl)amine) reacts with atmospheric CO2 to form a zinc carbonate species {[(NN3)Zn]3CO3}(NO3)4 (2(NO3)4), isolable as a crystalline product from organic solvents. The aqueous chemistry of the CO2 absorption and desorption processes for 1(NO3)2 and the presumed end-point of the reaction, 2(NO3)4, was unknown and hence investigated by NMR spectroscopy. Carboxylation of aqueous solutions of both 1(NO3)2 and 2(NO3)4 form products that can best be described as mixtures of monomeric [(NN3)ZnCO3H]+ and dimeric {[(NN3) Zn]2CO3}2+, which are in a dynamic equilibrium on the NMR time-scale. No evidence for the involvement of 2(NO3)4 in the carboxylation-decarboxylation processes is observed. Rather, the data suggest that 2 (NO3)4 provides [(NN3)Zn(OH2)]2+ that does not participate in the CO2 chemistry upon warming. A mechanism that is supported by NMR experiments and that accounts for the formation of [(NN3) ZnCO3H]+ and {[(NN3)Zn]2CO3}2+ from both ends of the reaction manifold is proposed.acceptedVersio