Tetramethoxypyrene-Based Biradical Donors with Tunable Physical and Magnetic Properties

Synthesis of 2,7-disubstituted tetramethoxypyrene-based neutral biradical donors is reported. The biradicals were characterized by EPR, UV–vis, CV, SQUID, and single-crystal X-ray diffraction, and their optical, electrochemical, and structural properties were compared and discussed. The experimental results are well supported by DFT calculations. Systematic tuning of magnetic exchange interactions was achieved by varying the radical moieties

Crystal Engineering of Tolane Bridged Nitronyl Nitroxide Biradicals: Candidates for Quantum Magnets

The tolane bridged nitronyl nitroxide biradicals with hydrogen bond donor and acceptor functional groups were synthesized. The magnetic measurements and the DFT calculations were performed to ascertain the influence of the functional groups on inter- and intramolecular magnetic exchange interactions. While upon functionalizing the tolane bridge the intramolecular exchange interactions remained nearly unchanged, the fine-tuning of intermolecular exchange interactions could be achieved by employing the crystal engineering approach

Crystal Engineering of Tolane Bridged Nitronyl Nitroxide Biradicals: Candidates for Quantum Magnets

The tolane bridged nitronyl nitroxide biradicals with hydrogen bond donor and acceptor functional groups were synthesized. The magnetic measurements and the DFT calculations were performed to ascertain the influence of the functional groups on inter- and intramolecular magnetic exchange interactions. While upon functionalizing the tolane bridge the intramolecular exchange interactions remained nearly unchanged, the fine-tuning of intermolecular exchange interactions could be achieved by employing the crystal engineering approach

Chemical Vapor Deposition of N‑Doped Graphene and Carbon Films: The Role of Precursors and Gas Phase

Thermally induced chemical vapor deposition (CVD) was used to study the formation of nitrogen-doped graphene and carbon films on copper from aliphatic nitrogen-containing precursors consisting of C₁- and C₂-units and (hetero)aromatic nitrogen-containing ring systems. The structure and quality of the resulting films were correlated to the influence of the functional groups of the precursor molecules and gas phase composition. They were analyzed with SEM, TEM, EDX, XPS, and Raman spectroscopy. The presence of (N-doped) graphene was confirmed by the 2D mode of the Raman spectra. The isolated graphene films obtained from nitrogen-containing precursors reveal a high conductivity and transparency compared to standard graphene CVD samples. Precursors with amine functional groups (<i>e.g.</i>, methylamine) can lead to a direct formation of graphene even without additional hydrogen present in the gas phase. This is not observed for, <i>e.g.</i>, methane under comparable CVD conditions. Therefore, the intermediate gas phase species (<i>e.g.</i>, amine radicals) can significantly enhance the graphene film growth kinetics. Kinetic and thermodynamic effects can be invoked to discuss the decay of the precursors

General Synthesis of MOF Nanotubes via Hydrogen-Bonded Organic Frameworks toward Efficient Hydrogen Evolution Electrocatalysts

The application scope of metal–organic frameworks (MOFs) can be extended by rationally designing the architecture and components of MOFs, which can be achieved via a metal-containing solid templated strategy. However, this strategy suffers from low efficiency and provides only one specific MOF from one template. Herein, we present a versatile templated strategy in which organic ligands are weaved into hydrogen-bonded organic frameworks (HOFs) for the controllable and scalable synthesis of MOF nanotubes. HOF nanowires assembled from benzene-1,3,5-tricarboxylic acid and melamine via a simple sonochemical approach serve as both the template and precursor to produce MOF nanotubes with varied metal compositions. Hybrid nanotubes containing nanometal crystals and N-doped graphene prepared through a carbonization process show that the optimized NiRuIr alloy@NG nanotube exhibits excellent electrocatalytic HER activity and durability in alkaline media, outperforming most reported catalysts. The strategy proposed here demonstrates a pioneering study of combination of HOF and MOF, which shows great potential in the design of other nanosized MOFs with various architectures and compositions for potential applications

Graphene Layer Encapsulation of Non-Noble Metal Nanoparticles as Acid-Stable Hydrogen Evolution Catalysts

Acid-stable, non-noble catalysts are promising for hydrogen evolution reaction (HER); however, they get easily damaged when used in acidic electrolytes, thus reducing the HER lifetimes. Moreover, completely blocking catalysts from acidic electrolytes degrades HER performance. To achieve a balance between the HER lifetime and performance, we vary the number of N-doped graphene layers (1–2, 2–3, and 3–5 layers) encapsulating NiMo nanoparticles as efficient HER catalysts and obtain the optimal number of protective layers. Our data show that 3–5 graphene layers achieved the best balance, with a stable current density of 100 mA cm^–2 for 25 h in 0.5 M H₂SO₄. Density functional theory calculations are performed to show the effect of encapsulating graphene layer number on the catalytic activity and protection of non-noble NiMo in acidic electrolytes

Chemical Selectivity at Grain Boundary Dislocations in Monolayer Mo_1–<i>x</i>W_<i>x</i>S₂ Transition Metal Dichalcogenides

Grain boundaries (GBs) are unavoidable crystal defects in polycrystalline materials and significantly influence their properties. However, the structure and chemistry of GBs in 2D transition metal dichalcogenide alloys have not been well established. Here we report significant chemical selectivity of transition metal atoms at GB dislocation cores in Mo_1–<i>x</i>W_<i>x</i>S₂ monolayers. Different from classical elastic field-driven dislocation segregation in bulk crystals, the chemical selectivity in the 2D crystals originates prominently from variation of atomic coordination numbers at dislocation cores. This observation provides atomic insights into the topological effect on the chemistry of crystal defects in 2D materials

Cooperation between holey graphene and NiMo alloy for hydrogen evolution in an acidic electrolyte

The development of noble-metal-free hydrogen evolution reaction (HER) materials for electrochemical water splitting is the key to achieving low-cost and efficient electrocatalysis that drives electrochemical hydrogen evolution. However, the electrocatalytic activities of most non-noble metals decrease in acidic electrolytes. Here, we have fabricated non-noble-metal electrodes using a bicontinuous and open porous NiMo alloy covered by nitrogen-doped (N-doped) graphene with nanometer-sized holes. This noble-metal-free HER catalyst exhibits performance almost identical with that of a Pt/C electrode, while its original catalytic activity is preserved even in acidic electrolytes. Density functional theory calculations indicate that the interfacial fringes between the nanoholes and NiMo surface induce charge transfer and promote hydrogen adsorption and desorption. The nanometer-sized holes simultaneously provide minimal surface area for chemical reactions, while delaying NiMo dissolution in excessive amounts of acidic electrolyte. Our method for the fabrication of the NiMo alloy provides a route to a promising class of electrochemical hydrogen-producing electrodes

Synthesis of Bisdesmosidic Oleanolic Acid Saponins via a Glycosylation-Deprotection Sequence under Continuous Microfluidic/Batch Conditions

We report the first synthesis of a series of bisdesmosidic oleanolic acid saponins using microflow reactor Comet X-01 via a continuous flow glycosylation-batch deprotection sequence. The main results of this study can be summarized as follows: (1) The microfluidic glycosylation of oleanolic acid at C-28 was achieved in quantitative yield and was applied to the synthesis of six C-28-monoglycosidic saponins. (2) The microfluidic glycosylation of oleanolic acid at C-3 was achieved in good yield without orthoester byproduct formation and was applied to the synthesis of three bisdesmosidic saponins. (3) The continuous synthesis of saponins via a microfluidic glycosylation-batch deprotection sequence was achieved in four steps involving two purifications. Thus, the continuous microfluidic glycosylation-deprotection process is expected to be suitable for the preparation of a library of bisdesmosidic oleanolic acid saponins for in vivo pharmacological studies