Stable Precursor Research Articles

In Situ Single-phase Formation of LaCl(CN2) Mixed-Anion Compound Via Controlled Pyrolysis of La3+ Modified Melamine Precursor.

Nitride (N3-) or cyanamide (CN22-) based mixed-anion compounds stand as attractive materials due to their unique properties derived from the binary or multiple anions, although their synthesis remains challenging in incorporating the N3- or CN22- anions safely. This work highlights the first demonstration of in situ single phase formation of a LaCl(CN2) mixed-anion compound from a stable single source precursor, melamine modified with LaCl3 preparable under aqueous conditions. The in situ formation of LaCl(CN2) involves the chemical modification of melamine with LaCl3 to form a complex. Upon heating of the precursor under N2 flowing, this complex generates cyanamide species around 400 °C, which react with LaCl3 and nonsublimated melamine to afford a binary LaCl(CN2)/g-C3N4 composite. Further pyrolysis at 800 °C decomposes the g-C3N4 counterpart, resulting in the LaCl(CN2) single-phase formation. The electronic properties of the precursor-derived single phase LaCl(CN2) were studied by the density functional theory calculation and UV-vis spectroscopy combined with X-ray photoelectron spectroscopy analyses and characterized by measuring 4.7, 1.8, and -2.9 eV for the band gap energy, the valence band maximum, and the conduction band minimum relative to Fermi energy, respectively. This study paves the way for exploring various cyanamide-based mixed anion compounds, advancing their potential applications in various fields.

Solvent‐ or Base‐Controlled Diastereoselectivity and Chemoselectivity for the Reaction of Ketenimine Zwitterionic Salts

Comprehensive SummaryKetenimine zwitterionic salt (KZS), a novel and stable ketenimine precursor, is still underexplored in the realm of chemical synthesis. In this study, we demonstrate the transformation of pyrrole derivatives through the cyclization of KZS with α‐aminoketones. The diastereoselectivity of this reaction is influenced by the solvent, enabling the isolation of 3‐hydroxypyrrolidine diastereomers with the highest reported dr value of 21 : 1. Furthermore, the chemoselectivity is modulated by the choice of base, yielding 2‐aminopyrrole derivatives as the major products. This research offers a sustainable approach to harnessing the potential of KZS in organic synthesis, contributing to a greener chemical process.

Stable and Versatile Pd Precursors for the Preparation of Robust Pd Catalysts under Continuous-Flow.

The chemical and engineering communities require the development of versatile precursors that can be used to synthesize robust catalysts to achieve global sustainability. To meet this demand, we developed a new Pd precursor for incorporating fine Pd metal into supports in a highly efficient manner. An atmospherically stable Pd precursor (Pd-80) was prepared by the thermally promoted aerobic oxidation of tetrakis(triphenylphosphine)palladium. The physical properties of Pd-80 were investigated using NMR spectroscopy, SEM, XPS, solvent-relaxation NMR spectroscopy, and dynamic light scattering (DLS) experiments. We also prepared a cordierite-supported Pd catalyst (Pd/cordierite) by stirring Pd-80 and cordierite powder in chloroform at room temperature. Pd/cordierite selectively catalyzes the hydrogenation of various reducible functional groups, including alkynes, azides, nitro groups, olefins, CO2Bn, N-Cbz, O-Bn, aromatic ketones, and styrene oxide, in continuous-flow hydrogenation reactions. The Pd/cordierite-catalyzed continuous-flow hydrogenation of nitrobenzene derivatives afforded the corresponding anilines, with catalyst activity maintained for over 250 h of continuous operation and a turnover number (TON) of 61,090 recorded.

Reinvigorating Photo-Activated R-Alkoxysilanes Containing 2-Nitrobenzyl Protecting Groups as Stable Precursors for Photo-Driven Si-O Bond Formation in Polymerization and Surface Modification.

This study aimed to revitalize silicon-based sol-gel chemistry methodologies utilizing photoprotected R-alkoxysilanes to control the synthesis of unique silicon-based materials. We have investigated the synthesis, characterization, light-induced deprotection, and subsequent polymerization/surface functionalization through the use of 2-nitrobenzyloxy-based photoremovable protecting groups (PPGs) as alkoxy reactive groups on ethyl and phenyl (R x -(alkoxy) y silanes, with x = 0-3 and y = 1-3). The photochemical dynamics, relative efficiencies, and kinetics of the novel alkoxysilane-based PPGs were thoroughly investigated using UV light irradiation by NMR and UV/vis methods. We then explored the tin-catalyzed coupling of photodeprotected products (R x -silanols) to form polymers/oligomers. We have found that photoenabled removal of PPGs and conversion to silanols from all silane systems studied is achieved. Furthermore, these deprotected species are polymerizable into siloxanes and effectively used as light-controlled surface modifiers with masking techniques of which proof-of-concept examples are given, enabling promising application as photolithographic reagents.

Double Spin with a Twist: Synthesis and Characterization of a Neutral Mixed-Valence Organic Stable Diradical.

A convenient design strategy opens access to neutral open-shell mixed-valence species via the redox transformation of charged stable precursors, i.e., the spiro-fused borate anions. We have implemented this strategy for the synthesis of the first neutral mixed-valence diradical: two neutral mixed-valence radical fragments were assembled via a twisted biphenyl bridge. The diradical is a crystalline solid obtained in almost quantitative yield by using a facile synthetic procedure. It is stable at room temperature in the triplet ground state with a very small singlet/triplet gap. This metal-free diradical can reversibly form five redox states. The diradical exhibits an intense IVCT band in the NIR region and can be assigned as a Class 2 Robin-Day MV (mixed valence) system with weakly interacting redox centers. Computations suggest that this diradical finds itself in a unique tug-of-war between two electron delocalization patterns, Kekulé and non-Kekulé, which gives rise to two geometric isomers that are close in energy but drastically different in spin distribution and polarity. Such bistable spin-systems should be intrinsically switchable and promising for the design of functional spin devices. The scope and limitations of the new redox-strategy for the neutral MV radicals were also tested on other types of spiro-fused borates, revealing structural factors responsible for the evolution from transient to persistent and then to stable radicals.

Methoxy Dioxasilepane: A Versatile and Stable Synthetic Precursor of Trimethoxysilane

This study introduces an aryl methoxy dioxasilepane as a versatile and stable precursor for aryltrimethoxysilanes. We conducted a quantitative assessment of the stability of this silicon moiety under acidic and basic conditions, demonstrating its superior stability compared to triethoxysilane, and methyl- or trifluoroethoxy dioxasilepanes. The synthetic utility of the methoxy dioxasilepane unit was further elucidated through an examination of its orthogonality and selective functionalization capabilities. Notably, we developed an efficient method for the conversion of a methoxy dioxasilepane to a trimethoxysilane. This method underscores the potential of a methoxy dioxasilepane as a surrogate in multistep syntheses of silanetriols, which offer advantages in the development of silicon-based bioisosteres for medicinal chemistry applications.

Photocurable Foam for Three-Dimensional-Printed Porous Structures.

In this research, a foam three-dimensional (3D) printing method using digital light processing (DLP) technology was developed to fabricate 3D-printed porous structures. To address the challenges in preparing DLP precursor foam fluid, we designed a specialized foaming device. This device enables the precursor solution to be blended with air, resulting in a stable foam precursor with an adjustable air/liquid fraction and suitable fluidity, crucially enhancing the gas-liquid contact time for the printing process. By manipulation of fluid flow rates, cycle counts, and gas/liquid ratios, one can easily prepare uniform foams with precise control over the pore size and porosity. To avoid significant volume reduction during ultraviolet (UV) curing, nanoparticle fillers were introduced into the network to prevent collapse of the foam structure. Furthermore, the inclusion of an UV absorber enhanced the quality of the printing process by addressing the limitations associated with particle scattering and reflection. The DLP process can readily fabricate intricate structures, featuring a planar resolution below 30 μm and a printing accuracy of less than 1%. Several examples were also demonstrated to highlight the advantages of this technology and its ability to directly print custom foam structures, thereby saving time and material resources.

Efficient Perovskite Light‐Emitting Diodes Processed with Green Solvents Enabling a Wide Antisolvent Time Window

AbstractGreen solvent processing of perovskite light‐emitting diodes (PeLEDs) is a necessity for their future commercialization. However, the almost insoluble nature of perovskites in most green solvents strongly impedes the progress of green solvent‐processed PeLEDs. Here, a novel green solvent triethylene glycol (TEG) is used as the processing solvent for perovskites. TEG has better solubility for perovskite precursors than most reported green solvents. Moreover, it is found that the low vapor pressure of TEG solvent and stable precursor solution render a much wider time window for the so‐called antisolvent treatment than that of perovskite precursor solution in commonly dimethyl sulfoxide. High‐quality perovskite film can be readily synthesized with the antisolvent treatment at a time window of 70–100 s, and the resultant green PeLEDs demonstrate nearly identical light‐emitting efficiencies. Together with further interface modification, the optimized green PeLEDs processed with TEG exhibit an external quantum efficiency of 20.4% and a maximal luminance over 38000 cd m−2. It is the first successful attempt to fabricate high‐efficiency PeLEDs utilizing green solvent and is enlightening for the development of high‐performance PeLEDs prepared with eco‐friendly solvents.

EFluorination for the Rapid Synthesis of Carbamoyl Fluorides from Oxamic Acids.

In this letter, we disclose the anodic oxidation of oxamic acids in the presence of Et3N·3HF as a practical, scalable, and robust method to rapidly access carbamoyl fluorides from readily available and stable precursors. The simplicity of this method also led us to develop the first flow electrochemical preparation of carbamoyl fluorides, demonstrating scale-up feasibility as a proof of concept.

Ion association behaviors in the initial stage of calcium carbonate formation: An ab initio study

In this work, we performed static density functional theory calculations and ab initio metadynamics simulations to systematically investigate the association mechanisms and dynamic structures of four kinds of ion pairs that could be formed before the nucleation of CaCO3. For Ca2+–HCO3− and Ca2+–CO32− pairs, the arrangement of ligands around Ca2+ evolves between the six-coordinated octahedral structure and the seven-coordinated pentagonal bipyramidal structure. The formation of ion pairs follows an associative ligand substitution mechanism. Compared with HCO3−, CO32− exhibits a stronger affinity to Ca2+, leading to the formation of a more stable precursor phase in the prenucleation stage, which promotes the subsequent CaCO3 nucleation. In alkaline environments, excessive OH− ions decrease the coordination preference of Ca2+. In this case, the formation of Ca(OH)+–CO32− and Ca(OH)2–CO32− pairs favors the dissociative ligand substitution mechanism. The inhibiting effects of OH− ion on the CaCO3 association can be interpreted from two aspects, i.e., (1) OH− neutralizes positive charges on Ca2+, decreases the electrostatic interactions between Ca2+ and CO32−, and thus hinders the formation of the CaCO3 monomer, and (2) OH− decreases the capacity of Ca2+ for accommodating O, making it easier to separate Ca2+ and CO32− ions. Our findings on the ion association behaviors in the initial stage of CaCO3 formation not only help scientists evaluate the impact of ocean acidification on biomineralization but also provide theoretical support for the discovery and development of more effective approaches to manage undesirable scaling issues.

Organophotocatalyzed Cross Coupling of C- and Si-Radical to Access Dibenzylic Silanes from para-Quinone Methides and Silanecarboxylic Acids.

Herein we present a catalytic cross-coupling strategy between C-radicals and Si-radicals, enabling the efficient, gentle, and versatile synthesis of dibenzylic silanes from para-quinone methides and silanecarboxylic acids as the stable silyl radical precursors. The reaction is facilitated by an inexpensive organophotocatalyst and exhibits broad compatibility with various electron-donating and electron-withdrawing functional groups. Notably, mechanistic investigations suggest the involvement of dibenzylic and silyl radicals, underscoring a novel radical coupling mechanism that introduces a fresh perspective on C-Si bond formation.

Low-resistivity molybdenum-carbide thin films formed by thermal atomic layer deposition with pressure-assisted decomposition reaction

The rapid increase in the resistivity of thin metal films as their thickness decreases to sub-10 nm, known as the resistivity size effect, is an important issue that must be addressed to ensure device performance in ultraminiaturized semiconductor devices. Molybdenum carbide (MoCx) has been studied as a candidate for emerging interconnection materials because it can maintain a low resistivity even at a low thickness. However, reports on stable precursors with guaranteed reactivity for atomic layer deposition (ALD) remain limited; moreover, the process of forming low-resistance MoCx thin films must be studied. In this study, we propose a new route to form low-resistivity MoCx thin films by thermal ALD with partial ligand dissociation by controlling the process pressure to enhance the reactivity of the Mo precursor with reactants. Following the proposed deposition process and subsequent annealing, uniform and continuous thin films were formed (even at a sub-5 nm thickness), with an extremely low resistivity of approximately 130 μΩ cm. Therefore, the proposed method can be applied as a next-generation interconnect process; notably, high-quality thin films can be formed through pressure-assisted decomposition, even with a lack of thermal energy during the ALD process.

Mullite-type Bi2Mn4O10 thin films prepared by a PVA-assisted sol–gel method

Mullite-type Bi2Mn4O10 is an attractive material for several potential applications, such as energy conversion and storage, data storage, batteries and photoelectrochemical devices. Bi2Mn4O10 thin films were prepared by sol–gel from a simple and highly stable precursor solution, based on the corresponding metal nitrate salts, acetic acid and polyvinyl alcohol. The films were deposited by dip-coating onto FTO substrates and dried at 350 °C; the dipping-drying cycle was repeated six times and the films were finally sintered at 600 °C. The films were characterized using GIXRD, revealing an excellent match with the ICDD database and previous studies. The UV–Vis measurements showed a direct band gap of 1.78 eV for the films. Raman spectroscopy permitted the identification of the Ag, B1g and B2g vibrational modes. The electrical properties via Hall effect measurements showed that the Bi2Mn4O10 thin films exhibit an n-type semiconductor behavior. Finally, the FESEM micrographs and AFM images revealed homogeneous, nanostructured thin films. In summary, through this comprehensive characterization, it was observed that high quality, nanocrystalline semiconductor thin films of Bi2Mn4O10 can be produced using this simple sol–gel method.

Time-varying characteristics of acoustic emission and fractals based on information dimension during structural failure of coal subjected to uniaxial compression

Uniaxial compression experiments were conducted on coal samples with different initial damage degrees, and the acoustic emission (AE) signals of the whole deformation and destruction process were captured synchronously. The distribution patterns of the acoustic emission signals at different loading stages were discussed. The chaotic system was introduced to process the acoustic emission series. The results indicate that the acoustic emission responses of coal samples with different damage levels had obvious stage characteristics during the whole destruction process. According to the information dimension fitting curves, the coal samples had good fractal characteristics in the whole loading process, and the value of information dimension decreased with the increased of threshold value.The information dimension of the acoustic emission energy signals showed a dynamic evolution law of “increase-decrease-increase” with time, and the rapid decreased of the information dimension could be used as a stable and effective precursor for predicting the macro-damage of coal.

Hydrothermally Assisted Conversion of Switchgrass into Hard Carbon as Anode Materials for Sodium-Ion Batteries.

Sodium-ion batteries (SIBs) are emerging as a viable alternative to lithium-ion batteries, reducing the reliance on scarce transition metals. Converting agricultural biomass into SIB anodes can remarkably enhance sustainability in both the agriculture and battery industries. However, the complex and costly synthesis and unsatisfactory electrochemical performance of biomass-derived hard carbon have hindered its further development. Herein, we employed a hydrothermally assisted carbonization process that converts switchgrass to battery-grade hard carbon capable of efficient Na-ion storage. The hydrothermal pretreatment effectively removed hemicellulose and impurities (e.g., lipids and ashes), creating thermally stable precursors suitable to produce hard carbon via carbonization. The elimination of hemicellulose and impurities contributes to a reduced surface area and lower oxygen content. With the modifications, the initial Coulombic efficiency (ICE) and cycling stability are improved concurrently. The optimized hard carbon showcased a high reversible specific capacity of 313.4 mAh g-1 at 100 mA g-1, a commendable ICE of 84.8%, and excellent cycling stability with a capacity retention of 308.4 mAh g-1 after 100 cycles. In short, this research introduces a cost-effective method for producing anode materials for SIBs and highlights a sustainable pathway for biomass utilization, underscoring mutual benefits for the energy and agricultural sectors.

Tuning catalytical properties of Pd/MWCNT nanoparticles via precursor variation in supercritical carbondioxide deposition

A practical, stable and non-conventional supercritical carbon dioxide deposition precursor was used to prepare Pd/MWCNT nanoparticles. The bis(2,2’bipyridyl)palladium(II) chloride precursor has a similar solubility value to commercially used precursors while advantageously it can be reduced at moderate temperatures. Palladium nanoparticles, whose particle size distribution were estimated around 10.5 nm, was deposited on multi-walled carbon nanotube support at 80 ºC and under 20.6 MPa. The catalyst showed higher performance for the selected model Suzuki-Miyaura cross-coupling reaction when compared with a similar catalyst which was prepared under similar supercritical conditions but from a different precursor. In general temperature and pressure is the main parameters to tune material properties for this method. Hence, this study reveals how different precursors in supercritical deposition method may affect the material properties for the target applications.

Chemical interaction between the sugar moieties in N, N-di-glycated alanine derivatives

The chemistry of N,N-diglycated amino acids remains unexplored due to their transient nature in the Maillard reaction. Their increased reactivity is attributed to the presence of high concentrations of open ring forms in at least one of their sugar moieties. The N,N-diglycated alanine derivatives were generated in situ via dissociation from their stable precursors the bis[N,N-diglycated alanine]iron(II) complexes, in the alanine/glucose/FeCl2 model system heated at 110 °C for 2 h. The thermal degradations of these complexes were followed in the reaction mixture, using isotope-labelled reactants, such as [13C-3] alanine and [13C–U] glucose, and ESI/qTOF/MS analysis. The N,N-diglycated amino acids exhibited a unique and characteristic chemical interaction between the neighbouring sugar moieties generating hitherto unknown heterocyclic moieties. The origin of these products was tracked by identifying ions incorporating one C-3 atom from alanine and between seven to 12 carbon atoms from the sugar moieties in the same structure. Temperature-dependent FTIR spectra of di-glycated alanine generated through ball milling provided further evidence for their reactivity.

High performance antimony-rich RexSb3Te for phase-change random access memory applications

Phase-change random access memory (PCRAM) demands for high-performance phase change materials, including operation speed, data retention, resistance drift etc. In this work, a high performance PCRAM device based on antimony-rich RexSb3Te material was put forward and studied. Excellent data retention, fast operation speed, low resistance drift, low power consumption and good cycle characteristics were achieved. The lattice information, bonding properties and surface morphology of the films were characterized by transmission electron microscopy, Raman spectroscopy and atomic force microscopy. Density functional theory calculations show that the Re dopant is more inclined to replace Sb and forms chemical bonds with Te, and the Re-Te bonds are more stable than the previous Sb-Te bonds, which is conducive to the formation of stable precursors to accelerate nucleation. The research shows that the antimony-rich Re0.18Sb3Te material has good overall performance, which provides a strategy for developing high-performance memory.

Unravelling the Mechanism of Electrochemically Induced Sol-Gel Depositions: pH Profiles Near Electrode and Influence on Film Growth

Electrochemically induced sol-gel depositions have become a widespread, versatile method for fabricating hybrid and nanostructured oxides on conductive substrates. The process is based on the buildup of electrochemically generated OH− in the diffusion layer near the electrode surface. For the electrodeposition of silica thin films, these OH− ions catalyze the gelation of a kinetically stable precursor solution, thereby resulting in an electrochemically controlled process. The control of the diffusion layer has proven pivotal to depositing thin films while preventing the formation of aggregated by-products deeper in the solution. In this work, the silica sol-gel reactions and electrochemical OH− generation were critically analyzed and described to gain insight into the deposition mechanism. A general model is proposed that predicts the pH profile during both stationary and rotating disk electrode depositions under different conditions (i.e., current densities, times, and rotation rates). This model provides insights into the reactive zones where gelation occurs, and explains typical phenomena observed during deposition such as the dependence of film growth rates and aggregate formation on the deposition conditions. The insights and expressions obtained in this work are invaluable when designing future experiments using novel chemistries or setups.

Mass spectrometry-based metabolomics for the elucidation of alkaloid biosynthesis and function in invasive Vincetoxicum rossicum populations

The genus Vincetoxicum includes a couple of highly invasive vines in North America that threaten biodiversity and challenge land management strategies. Vincetoxicum species are known to produce bioactive phenanthroindolizidine alkaloids that might play a role in the invasiveness of these plants via chemical interactions with other organisms. Untargeted, high-resolution mass spectrometry-based metabolomics approaches were used to explore specialized metabolism in Vincetoxicum plants collected from invaded sites in Ontario, Canada. All metabolites corresponding to alkaloids in lab and field samples of V. rossicum and V. nigrum were identified, which collectively contained 25 different alkaloidal features. The biosynthesis of these alkaloids was investigated by the incorporation of the stable isotope-labelled phenylalanine precursor providing a basis for an updated biosynthetic pathway accounting for the rapid generation of chemical diversity in invasive Vincetoxicum. Aqueous extracts of aerial Vincetoxicum rossicum foliage had phytotoxic activity against seedlings of several species, resulting in identification of tylophorine as a phytotoxin; tylophorine and 14 other alkaloids from Vincetoxicum accumulated in soils associated with full-sun and a high-density of V. rossicum. Using desorption-electrospray ionization mass spectrometry, 15 alkaloids were found to accumulate at wounded sites of V. rossicum leaves, a chemical cocktail that would be encountered by feeding herbivores. Understanding the specialized metabolism of V. rossicum provides insight into the roles and influences of phenanthroindolizidine alkaloids in ecological systems and enables potential, natural product-based approaches for the control of invasive Vincetoxicum and other weedy species.