Deciphering the Spatial Arrangement of Metals and Correlation to Reactivity in Multivariate Metal–Organic Frameworks

Thirty-six porphyrin-based metal–organic frameworks (MOFs) with composition of <b>(M</b>_<b>3</b><b>O)</b>_<b>2</b><b>(TCPP-M)</b>_<b>3</b> and M₃O trigonal SBUs of various metals, Mg₃O, Mn₃O, Co₃O, Ni₃O, and Fe₃O including mixed-metal SBUs, Mn_<i>x</i>Fe_3–<i>x</i>O, Ni_<i>x</i>Fe_3–<i>x</i>O, Co_<i>x</i>Ni_3–<i>x</i>O, Mn_<i>x</i>Co_3–<i>x</i>O, Mn_<i>x</i>Mg_3–<i>x</i>O, and Mn_<i>x</i>Ni_3–<i>x</i>O were synthesized and characterized. These multivariate MOFs (MTV-MOFs) were examined by X-ray photoelectron spectroscopy, UV–vis diffuse reflectance spectra, and for the first time, their metal spatial arrangement deciphered and were found to exist in the form of either domains or well-mixed. We find that MTV-MOFs with well-mixed metals in their SBUs, rather than the SBUs having one kind of metal but different from one SBU to another, perform better than the sum of their parts in the test reaction involving the photo-oxidation of 1,5-dihydroxynaphthalene

Oxygen Vacancies and Stacking Faults Introduced by Low-Temperature Reduction Improve the Electrochemical Properties of Li₂MnO₃ Nanobelts as Lithium-Ion Battery Cathodes

Among the Li-rich layered oxides Li₂MnO₃ has significant theoretical capacity as a cathode material for Li-ion batteries. Pristine Li₂MnO₃ generally has to be electrochemically activated in the first charge–discharge cycle which causes very low Coulombic efficiency and thus deteriorates its electrochemical properties. In this work, we show that low-temperature reduction can produce a large amount of structural defects such as oxygen vacancies, stacking faults, and orthorhombic LiMnO₂ in Li₂MnO₃. The Rietveld refinement analysis shows that, after a reduction reaction with stearic acid at 340 °C for 8 h, pristine Li₂MnO₃ changes into a Li₂MnO₃–LiMnO₂ (0.71/0.29) composite, and the monoclinic Li₂MnO₃ changes from Li_2.04Mn_0.96O₃ in the pristine Li₂MnO₃ (P–Li₂MnO₃) to Li_2.1Mn_0.9O_2.79 in the reduced Li₂MnO₃ (R-Li₂MnO₃), indicating the production of a large amount of oxygen vacancies in the R-Li₂MnO₃. High-resolution transmission electron microscope images show that a high density of stacking faults is also introduced by the low-temperature reduction. When measured as a cathode material for Li-ion batteries, R-Li₂MnO₃ shows much better electrochemical properties than P-Li₂MnO₃. For example, when charged–discharged galvanostatically at 20 mA·g^–1 in a voltage window of 2.0–4.8 V, R-Li₂MnO₃ has Coulombic efficiency of 77.1% in the first charge–discharge cycle, with discharge capacities of 213.8 and 200.5 mA·h·g^–1 in the 20th and 30th cycles, respectively. In contrast, under the same charge–discharge conditions, P-Li₂MnO₃ has Coulombic efficiency of 33.6% in the first charge–discharge cycle, with small discharge capacities of 80.5 and 69.8 mA·h·g^–1 in the 20th and 30th cycles, respectively. These materials characterizations, and electrochemical measurements show that low-temperature reduction is one of the effective ways to enhance the performances of Li₂MnO₃ as a cathode material for Li-ion batteries

Silver(I)-Catalyzed Atroposelective Desymmetrization of <i>N</i>‑Arylmaleimide via 1,3-Dipolar Cycloaddition of Azomethine Ylides: Access to Octahydropyrrolo[3,4‑<i>c</i>]pyrrole Derivatives

A highly efficient Ag­(I)-catalyzed atroposelective desymmetrization of <i>N</i>-(2-<i>t</i>-butylphenyl)­maleimide via 1,3-dipolar cycloaddition of in situ generated azomethine ylides has been established successfully, affording a facile access to a series of biologically important and enantioenriched octahydropyrrolo­[3,4-<i>c</i>]­pyrrole derivatives in generally high yields (up to 99%) with excellent levels of diastereo-/enantioselectivities (up to 99% ee, >20:1 dr). Subsequent transformations led to fascinating 2<i>H</i>-pyrrole and polysubstituted pyrrole compounds without loss of stereoselectivity. The absolute configuration of the generated chiral axis has been unambiguously identified as (<i>M</i>) through single-crystal X-ray diffraction analysis. Furthermore, on the basis of the comprehensive experimental results and the absolute configuration of one of the cycloadducts, the origin of the stereoselectivity was proposed to be attributed to the steric congestion imposed by the bulky PPh₂ group of the chiral ligand and the <i>tert</i>-butyl group of <i>N</i>-(2-<i>t</i>-butylphenyl)­maleimide. The possible hydrogen bond interaction between the NH₂ group of the chiral ligand and one of the carbonyl groups of <i>N</i>-(2-<i>t</i>-butylphenyl)­maleimide is considered to facilitate stabilizing the transition state

Ag(I)-Catalyzed Kinetic Resolution of Cyclopentene-1,3-diones

An efficient kinetic resolution of readily available racemic cyclopentene-1,3-diones has been developed via a Ag­(I)-catalyzed asymmetric 1,3-dipolar cycloaddition of azomethine ylides. This methodology shows good functional-group tolerance, delivering an array of synthetically valuable cyclopentene-1,3-diones with excellent stereoselectivity and generally high resolution efficiency (<i>s</i> = 48–226) accompanied by the biologically important fused pyrrolidine derivatives. Notably, this strategy allows facile access to the key intermediates for the synthesis of (+)-madindolines A and B

Ag(I)-Catalyzed Kinetic Resolution of Cyclopentene-1,3-diones

An efficient kinetic resolution of readily available racemic cyclopentene-1,3-diones has been developed via a Ag­(I)-catalyzed asymmetric 1,3-dipolar cycloaddition of azomethine ylides. This methodology shows good functional-group tolerance, delivering an array of synthetically valuable cyclopentene-1,3-diones with excellent stereoselectivity and generally high resolution efficiency (<i>s</i> = 48–226) accompanied by the biologically important fused pyrrolidine derivatives. Notably, this strategy allows facile access to the key intermediates for the synthesis of (+)-madindolines A and B

π‑Extended Benzoporphyrin-Based Metal–Organic Framework for Inhibition of Tumor Metastasis

We report on the benzoporphyrin-based metal–organic framework (TBP-MOF), with 10-connected Zr₆ cluster and much improved photophysical properties over the traditional porphyrin-based MOFs. It was found that TBP-MOF exhibited red-shifted absorption bands and strong near-infrared luminescence for bioimaging, whereas the π-extended benzoporphyrin-based linkers of TBP-MOF facilitated ¹O₂ generation to enhance O₂-dependent photodynamic therapy (PDT). It was demonstrated that poly­(ethylene glycol)-modified nanoscale TBP-MOF (TBP-nMOF) can be used as an effective PDT agent under hypoxic tumor microenvironment. We also elucidated that the low O₂-dependent PDT of TBP-nMOF in combination with αPD-1 checkpoint blockade therapy can not only suppress the growth of primary tumor, but also stimulate an antitumor immune response for inhibiting metastatic tumor growth. We believe this TBP-nMOF has great potential to serve as an efficient photosensitizer for PDT and cancer immunotherapy

Highly Active Carbon Supported Pd–Ag Nanofacets Catalysts for Hydrogen Production from HCOOH

Hydrogen is regarded as a future sustainable and clean energy carrier. Formic acid is a safe and sustainable hydrogen storage medium with many advantages, including high hydrogen content, nontoxicity, and low cost. In this work, a series of highly active catalysts for hydrogen production from formic acid are successfully synthesized by controllably depositing Pd onto Ag nanoplates with different Ag nanofacets, such as Ag{111}, Ag{100}, and the nanofacet on hexagonal close packing Ag crystal (Ag­{hcp}). Then, the Pd–Ag nanoplate catalysts are supported on Vulcan XC-72 carbon black to prevent the aggregation of the catalysts. The research reveals that the high activity is attributed to the formation of Pd–Ag alloy nanofacets, such as Pd–Ag{111}, Pd–Ag{100}, and Pd–Ag­{hcp}. The activity order of these Pd-decorated Ag nanofacets is Pd–Ag­{hcp} > Pd–Ag{111} > Pd–Ag{100}. Particularly, the activity of Pd–Ag­{hcp} is up to an extremely high value, i.e., TOF_{hcp} = 19 000 ± 1630 h^–1 at 90 °C (lower limit value), which is more than 800 times higher than our previous quasi-spherical Pd–Ag alloy nanocatalyst. The initial activity of Pd–Ag­{hcp} even reaches (3.13 ± 0.19) × 10⁶ h^–1 at 90 °C. This research not only presents highly active catalysts for hydrogen generation but also shows that the facet on the hcp Ag crystal can act as a potentially highly active catalyst

Mechanically Strong Multifilament Fibers Spun from Cellulose Solution via Inducing Formation of Nanofibers

Mechanically strong cellulose fibers spun with environmentally friendly technology have been under tremendous consideration in the textile industry. Here, by inducing the nanofibrous structure formation, a novel cellulose fiber with high strength has been designed and spun successfully on a lab-scale spinning machine. The cellulose–NaOH–urea solution containing 0.5 wt % LiOH was regenerated in 15 wt % phytic acid/5 wt % Na₂SO₄ aqueous solution at 5 °C, in which the alkali–urea complex as shell on the cellulose chain was destroyed, so the naked stiff macromolecules aggregated sufficiently in a parallel manner to form nanofibers with apparent average diameter of 25 nm. The cellulose fibers consisting of the nanofibers exhibited high degree of orientation with Herman’s parameter of 0.9 and excellent mechanical properties with tensile strength of 3.5 cN/dtex in the dry state and 2.5 cN/dtex in the wet state, as well as low fibrillation. This work provided a novel approach to produce high-quality cellulose multifilament with nanofibrous structure, showing a great potential in the material processing

Dynamic Hosts for High-Performance Li–S Batteries Studied by Cryogenic Transmission Electron Microscopy and in Situ X‑ray Diffraction

Developing a high-performance sulfur host is central to the commercialization and general development of lithium–sulfur batteries. Here, for the first time, we propose the concept of dynamic hosts for lithium–sulfur batteries and elucidate the mechanism through which TiS₂ acts in such a fashion, using in situ X-ray diffraction and cryogenic scanning transmission electron microscopy (cryo-STEM). A TiS₂–S composite electrode delivered a reversible capacity of 1120 mAh g^–1 at 0.3 C after 200 cycles with a capacity retention of 97.0% and capacities of 886 and 613 mAh g^–1 at 1.0 C up to 200 and 1000 cycles, respectively. Our results indicate that it is Li_<i>x</i>TiS₂ (0 < <i>x</i> ≤ 1), rather than TiS₂, that effectively traps polysulfides and catalytically decomposes Li₂S