Sp2 Carbon Research Articles

Magnetic quantum phase transition extension in strained P-doped graphene.

We explore quantum-thermodynamic effects in a phosphorous (P)-doped graphene monolayer subjected to biaxial tensile strain. Introducing substitutional P atoms in the graphene lattice generates a tunable spin magnetic moment controlled by the strain control parameter ε. This leads to a magnetic quantum phase transition (MQPT) at zero temperature modulated by ε. The system transitions from a magnetic phase, characterized by an out-of-plane sp3 type hybridization of the P-carbon (P-C) bonds, to a non-magnetic phase when these bonds switch to in-plane sp2 hybridization. Employing a Fermi-Dirac statistical model, we calculate key thermodynamic quantities such as the electronic entropy Se and electronic specific heat Ce. At finite temperatures, we find a MQPT extension characterized by Se and Ce, where both display a distinctive Λ-shape profile as a function of ε. These thermodynamic quantities sharply increase up to ε = 5% in the magnetic regime, followed by a sudden drop at ε = 5.5%, transitioning to a linear dependence on ε in the nonmagnetic regime. This controllable magnetic-to-nonmagnetic switch offers potential applications in electronic nanodevices operating at finite temperatures.

Total Synthesis of Discobahamin A and Putative Structure of Discobahamin B via an Isocyanide‐based Macrocyclization

We report in this paper the first total synthesis of discobahamin A, a 24‐membered macrocyclopeptide containing an α‐keto amide functional group. We assign the absolute configuration of 2‐hydroxy‐3‐methylpentanoic acid (Hmp), the side chain capping the N‐terminus of the macrocycle, as the (2S, 3S) stereoisomer. A novel macrocyclization strategy was developed, utilizing an intramolecular Passerini reaction between ω‐isocyano aldehyde and acetic acid. Notably, this macrocyclization proceeds via C(sp3)‐C(sp2) bond formation and de novo generation of an a‐keto amide functional group. Furthermore, we synthesized both the proposed structure of discobahamin B (5) and its diastereomer. However, the spectroscopic data for these two compounds do not fully align with those reported for discobahamin B (5).

Total Synthesis of Discobahamin A and Putative Structure of Discobahamin B via an Isocyanide-based Macrocyclization.

We report in this paper the first total synthesis of discobahamin A, a 24-membered macrocyclopeptide containing anα-keto amide functional group. We assign the absolute configuration of 2-hydroxy-3-methylpentanoic acid (Hmp), the side chain capping the N-terminus of the macrocycle, as the (2S, 3S) stereoisomer. A novel macrocyclization strategy was developed, utilizingan intramolecular Passerini reaction betweenω-isocyano aldehyde and acetic acid. Notably, this macrocyclization proceedsviaC(sp3)-C(sp2) bond formation andde novogeneration of ana-keto amide functional group. Furthermore, we synthesized both the proposed structure ofdiscobahamin B (5) and its diastereomer. However, the spectroscopic data for these two compounds do not fully align with those reported for discobahamin B (5).

Coalescence of carbon nanotubes while preserving the chiral angles.

Atomically precise coalescence of graphitic nanocarbon molecules is one of the most challenging reactions in sp2 carbon chemistry. Here, we demonstrate that two carbon nanotubes with the same chiral indices (n, m) are efficiently coalesced into a single (2n, 2 m) nanotube with preserved chiral angles via heat treatment at less than 1000 °C. The (2n, 2 m) nanotubes constitute up to ≈ 20%-40% of the final sample in the most efficient case. Additional optical absorption peaks of the (2n, 2 m) nanotubes emerge, indicating that the reaction occurs over the entire sample. The reaction efficiency strongly depends on the chiral angle, implying that C-C bond cleavage and recombination occurs sequentially. Furthermore, the reaction occurs efficiently even at 600 °C in an atmosphere containing trace amounts of oxygen. These findings offer routes for the structure-selective synthesis of large-diameter nanotubes and modification of the properties of nanotube assemblies via postprocessing.

A Pre‐Coordinated Strategy Precisely Tailors the Coordination Structure of Single‐Atom Sites Toward Efficient Catalysis

AbstractCoordination structure engineering represents a promising approach for optimizing the catalytic properties of single‐atom catalysts (SACs). However, the precise tailoring of single‐atom sites remains challenging. Herein, a pre‐coordination strategy is proposed to design SACs with tunable local coordination environments on 2D honeycomb‐like carbon nanofoams. By pre‐coordinating the metal precursor with customized functional groups on a layered Mg(OH)2 template through strong d‐p orbital hybridization, SACs featuring Co─N4 (Co1/NC), Co─C4 (Co1/CC), and Co─C2S2 (Co1/CSC) configurations are fabricated. The lamellar honeycomb‐like architecture facilitates active site exposure, reactant enrichment, and mass transfer during the reaction process. Consequently, the Co1/NC catalyst, despite its extremely low Co loading of 0.12 wt.%, demonstrates exceptional catalytic activity and stability for nitroaromatics reduction, achieving an impressive overall turnover frequency (TOF) of 73668 h−1 for the conversion of 4‐nitrophenol to 4‐nitroaniline, surpassing most reported catalysts. Theoretical calculations indicate the Co─N4 configuration possesses moderate Fermi electronic states compared to Co─C4 and Co─C2S2, significantly promoting the formation and utilization of reactive H* species and accelerating the reaction kinetics for aromatic nitroreduction. This work establishes a novel avenue for the meticulous manipulation of coordination structures in SACs, paving the way for the advancement of sophisticated catalytic materials for chemical transformations.

Pd-Catalyzed Skeletal Rearrangement via C(sp³)-C(sp³) Activation to Access α,β-Unsaturated δ/γ-Lactone.

The activation of non-polar aliphatic C-C bonds represents a significant challenge that remains to be addressed in the field of Pd(II) catalysis. In this study, we present a dual ligand approach as a means of addressing this issue. The process entails lactonization of cyclobutane and cyclopropane carboxylic acid via the activation of non-polar C(sp³)-C(sp³) bond despite the high feasibility of both ortho-C(sp2)-H and β or γ-C(sp3)-H activation. Density Functional Theory (DFT) calculations were performed to reveal the mechanistic insights and elucidate the role of dual ligands in facilitating this challenging transformation.

Pd-Catalyzed Allylic Substitution of Azo-Ene Adducts Enables Net Allylic C-H Alkylation of Allylic Alcohols.

We present a protocol for a regioselective allylic C-H alkylation of allylic alcohols, consisting of a sequential azo-ene reaction and attendant Pd-catalyzed allylic substitution with Grignard reagents. Notable features of this work include: (1) regioselective C(sp3)-C(sp3) bond formation is achieved under Pd-catalysis, and (2) the allylic substitution proceeds with retention of configuration at the electrophilic allylic carbon as well as the olefin geometry.

Pd‐Catalyzed Skeletal Rearrangement via C(sp³)−C(sp³) Activation to Access α,β‐Unsaturated δ/γ‐Lactone

The activation of non‐polar aliphatic C−C bonds represents a significant challenge that remains to be addressed in the field of Pd(II) catalysis. In this study, we present a dual ligand approach as a means of addressing this issue. The process entails lactonization of cyclobutane and cyclopropane carboxylic acid via the activation of non‐polar C(sp³)−C(sp³) bond despite the high feasibility of both ortho−C(sp2)−H and β or γ−C(sp3)−H activation. Density Functional Theory (DFT) calculations were performed to reveal the mechanistic insights and elucidate the role of dual ligands in facilitating this challenging transformation.

Activating and Stabilizing ORR in P2-type Cathode by Modulating Orbital Hybridization and Local Covalency towards High-Rate and Long-Cycle Sodium-Ion Batteries

Activating and Stabilizing ORR in P2-type Cathode by Modulating Orbital Hybridization and Local Covalency towards High-Rate and Long-Cycle Sodium-Ion Batteries

High-Dielectric 2D Bismuth Oxides with Large Bandgaps: The Role of 6s2 Lone Pair Hybridization.

Large-bandgap and high-dielectric 2D dielectrics are crucial for transistor performance because they maximize gate-to-channel capacitive coupling, yet such high-quality materials remain scarce. This study employed first-principles calculations to predict 18 distinct 2D bismuth oxides (BiOs). It is demonstrated that the 6s2 lone pairs in 2D BiOs form benign positive feedback between the bandgap and dielectric constant. The hybridization of 6s2 and 6pz orbitals is key to setting the bandgap, revealing a significant negative linear relationship between the bond length and energy gap. In particular, due to the stereochemical activity of 6s2 that enhances the ionic contribution, these materials are capable of sustaining a high dielectric constant value surpassing 24, even within bandgaps wider than 4 eV. This discovery enhances the theoretical understanding of 2D materials exhibiting large bandgaps and high dielectric constants, providing deeper insights into the impact of lone pairs on 2D materials.

Sequential Conversion of Vinyl Triflates to 1,2-Disilanes via Technical Control of Magnesium and Calcium Reducibility Differences.

Reductive direct substitution of α-arylvinyl triflates on the sp2 carbon atom by magnesium in the presence of chlorosilane proceeded to give the corresponding α-silylstyrenes, which could not be reduced further, and the reaction completely stopped because the reduction potential of α-silylstyrenes lies out of the reducible field of magnesium. The subsequent reduction of α-silylstyrenes by calcium brought about the second introduction of another silyl group to the vicinal carbon atom to lead a selective and simple route to a variety of 1,2-disilanes from vinyl triflates by cooperative works of magnesium and calcium with different reduction potentiality.

Stereoselective Copper-Catalyzed Cross-Coupling of α-CF3-Allylboronic Acids with Diazoketones.

We have studied copper-catalyzed cross-coupling of chiral α-CF3-substituted allylboronic acids with α-diazoketones. The reaction proceeds with excellent regioselectivity and stereoselectivity via allylic rearrangement. The method is useful for formation a new allylic C(sp3)-C(sp3) bond with high selectivity. The poor yield is a limitation of this reaction.

Oxygen Evolution Reaction of Amorphous/Crystalline Composites of NiFe(OH)x/NiFe2O4.

Orbital structures are strongly correlated with catalytic performance, whereas their regulation strategy is still in pursuit. Herein, the Fe 3d and O 2p orbital hybridization was optimized by controlling the content of amorphous NiFe(OH)x (a-NiFe(OH)x), which was grown in situ on crystalline NiFe2O4 (c-NiFe2O4) using an ultrasonic reduction method. The results of electron energy loss spectroscopy (EELS) and X-ray absorption spectra (XAS) revealed that the Fe-Oa orbital hybridization in a-NiFe(OH)x is effectively strengthened by jointing with the adjacent oxygen (Oc) in c-NiFe2O4, which is further confirmed by the higher antibonding orbital energies based on density functional theory (DFT) calculations. The resultant Oa-Fe-Oc at the composite interface leads to balanced adsorption and desorption energies. Accordingly, the optimal composite with strong Fe 3d-O 2p hybridization results in enhanced OER performance, and the overpotential is 150 mV, lower than that of the pristine sample. This work represents a promising approach to orbital hybridization via the introduction of an amorphous phase to construct highly efficient catalysts.

Localized Effects in Graphene Oxide Systems: A Pathway to Hyperbolic Metamaterials

Graphene oxide (GO) has emerged as a carbon-based nanomaterial providing a different pathway to graphene. One of its most notable features is the ability to partially reduce it, resulting in graphene-like sheets through the elimination of oxygen-including functional groups. In this paper, the effect of localized interactions in an Ag/GO/Au multilayer system was studied to explore its potential for photonic applications. GO was dip-coated onto magnetron-sputtered silver, followed by the deposition of a thin gold film to form an Ag/GO/Au structure. Micro-Raman Spectroscopy, SEM and Variable Angle Ellipsometry (VASE) measurements were performed on the Ag/GO/Au structure. An interesting behavior of the GO deposited on magnetron-sputtered silver with the formation of Ag nanostructures on top of the GO layer is reported. In addition to typical GO bands, Micro-Raman analysis reveals peaks such as the 1478 cm−1 band, indicating a transition from sp3 to sp2 hybridization, confirming the partial reduction of GO. Additionally, calculations based on effective medium theory (EMT) highlight the potential of Ag/GO structures in hyperbolic metamaterials for photonics. The medium exhibits dielectric behavior up to 323 nm, transitions to type I HMM between 323 and 400 nm and undergoes an Epsilon Near Zero and Pole (ENZP) transition at 400 nm, followed by type II HMM behavior.

A planar-sheet nongraphitic zero-bandgap sp2 carbon phase made by the low-temperature reaction of γ-graphyne

The highest sheet symmetry form of graphyne, with one triple bond between each neighboring hexagon in graphene, irreversibly transforms exothermically at ambient pressure and low temperatures into a nongraphitic, planar-sheet, zero-bandgap phase consisting of intrasheet-bonded sp2 carbons. The synthesis of this sp2 carbon phase is demonstrated, and other carbon phases are described for possible future synthesis from graphyne without breaking graphyne bonds. While measurements and theory indicate that the reacting graphyne becomes nonplanar because of sheet wrinkling produced by dimensional mismatch between reacted and nonreacted sheet regions, sheet planarity is regained when the reaction is complete. Although the observed elimination of triple bonds to make parallel planar sp2 carbon sheets likely requires ordered transformation within each sheet, diffraction data for reacted multisheet stacks indicate that the relative lateral positions of neighboring sheets are disordered, as predicted, since no crystalline diffraction peak (other than for the intersheet spacing) is observed.

Electromagnetism and thermostability of Cr7C3synthesised with high-temperature and high-pressure quenching method.

The interactions between the carbon skeleton and the metal atoms of a binary transition metal carbide (BTMC) are particular interest for industrial applications with openning physics and chemitry questions, especially in magnetoelectric (ME) functional materials and cemented carbides. Chromium and carbon BTMCs are a series of intermetallic compounds with typical chemical formulas and sharepolycrystalline powder c somehromium special characteristics.and carbon as precursors, In this paper,and synthesized s we usedingle-phase bluk Cr7C3 (orthorhombic, with space group: Pnma) with high density and good crystallinity by means of high-temperature and high-pressure quenching method (HTHPQM). We studied the material properties and electronic structures of Cr7C3studied with both experimental measurements and Density Functional Theory (DFT) ab intio simulations, and found that Cr7C3 is acompaction conductor(97.2 %), with anexcellent electrical conductivitythermostability (oxidation (2.32 10×at 1175 -3K)Ω·m), relative highand a magnetic phase transition from paramagnetism to soft ferromagnetism around 50 K, and the electromagnetic propertities are chiefly due to the abundancy of the 3d electrons of Cr, and the orbital hybridization between C and Cr with their 2p and 3d electrons is the reason for the crystal sturcture and high thermostability. Therefore, the prepared Cr7C3 is multifunctional material with better application prospects, and the HPHTQM is a simple and effective mothed to prepare samples as BTMCs.&#xD.

Pinpointing the CN Stretch Frequency of Neutral Cyano-Polycyclic Aromatic Hydrocarbons: A Laboratory and Quantum Chemical Spectroscopic Study of 9-Cyanoanthracene.

The CN stretch frequency of neutral, gas-phase 9-cyanoanthracene is 2207 cm-1 (4.531 μm) based on high-resolution infrared absorption experiments coupled with a new hybrid anharmonic quantum chemical methodology. A broad band (full-width at half-maximum of 47 cm-1) is observed and assigned to multiple transitions, including the CN stretch fundamental and various combination bands that gather intensity from strong anharmonic coupling with the bright CN stretch. The new hybrid computational approach utilizes the harmonic force constants from the double-hybrid rev-DSDPBEP86 functional that includes MP2 electron correlation, and the cubic and quartic force constants from the B3LYP density functional. In combination, this method computes a band center of 2207 cm-1 for 9-cyanoanthracene, a direct match with experiment. Further, the hybrid method produces a difference of less than 1 cm-1 for the two isomers of cyanonaphthalene and cyanobenzene. As shown from comparison with CCSD(T)-F12b anharmonic frequency computations of cyanobenzene, inclusion of electron correlation is required to properly characterize the electronic structure of the highly electron withdrawing CN group on polycyclic aromatic hydrocarbons. In agreement with earlier studies, computation of the CN stretch of 14 small CN-PAHs produces a narrow (∼20 cm-1) band from 2207-2229 cm-1 (4.53-4.48 μm). The remainder of the spectrum below 2000 cm-1 and from 3000-3120 cm-1 shows good agreement between experiment and the hybrid theory with a mean absolute error of 16 and 14 cm-1, respectively.

Enantioselective reductive cross-couplings to forge C(sp2)–C(sp3) bonds by merging electrochemistry with nickel catalysis

Motivated by the inherent benefits of synergistically combining electrochemical methodologies with nickel catalysis, we present here a Ni-catalyzed enantioselective electroreductive cross-coupling of benzyl chlorides with aryl halides, yielding chiral 1,1-diaryl compounds with good to excellent enantioselectivity. This catalytic reaction can not only be applied to aryl chlorides/bromides, which are challenging to access by other means, but also to benzyl chlorides containing silicon groups. Additionally, the absence of a sacrificial anode lays a foundation for scalability. The combination of cyclic voltammetry analysis with electrode potential studies suggests that NiI species activate aryl halides via oxidative addition and alkyl chlorides via single electron transfer.

Tailoring conductive polyvinyl alcohol nanofibers: thermal-induced structural evolution in nitrogen for energy storage device

Carbon fibers from polyvinyl alcohol (PVA) was achieved by the electrospinning technique, which was subsequently followed by the stabilization and carbonization of electrospun PVA fibers. The XRD pattern of PVA fiber confirms the change in the structure of PVA nanofibers and carbonized PVA from temperatures of 200, 300, 400, 500, and 700 °C, resulting in a structural evolution from fibrous to plate-like and dot carbon compounds. The SEM image of the PVA precursor reveals the presence of fibers exhibiting a smooth surface following the stabilization and carbonization processes at temperatures below 500 °C. Furthermore, the image depicts fibers that melt and transform into a carbon layer at a higher carbonization temperature ranging from 600 to 700 °C. TEM results show the formation of carbon sheets and dots, with an average diameter of 8.2 nm. The evolution that occurs from fibers to carbon sheet due to the melting process indicates a change in the morphology of 1D to graphenic carbon. The identification of carbon–oxygen functional groups, such as C = C (carbon with sp2 hybridization), C–C (carbon with sp3 hybridization), and C = O bonds, has been successfully detected and analysed using both XPS and Raman spectroscopy techniques. The results of the XPS profile fitting, as proven by Raman spectra, produce a graphenic carbon containing a 2D structure, with the total sp2 fraction increasing in the increasing carbonization temperature. This is also followed by significantly increasing electrical conductivity. So, the carbonized PVA nanofiber has the potential to be applied in electronic and energy storage device applications. This is also followed by an increase in electrical conductivity due to the formation of more carbon functional groups compared to less oxygen. Thus, carbonized PVA nanofibers have great potential for application in electronic devices and energy storage applications such as batteries and supercapacitors.

Palladium-Catalyzed Oxidative Allene-Allene Cross-Coupling.

Direct cross-coupling reactions between two similar unactivated partners are challenging but constitute a powerful strategy for the creation of new carbon-carbon bonds in organic synthesis. [4]Dendralenes are a class of acyclic branched conjugated oligoenes with great synthetic potential for the rapid generation of structural complexity, yet the chemistry of [4]dendralenes remains an unexplored field due to their limited accessibility. Herein, we report a highly selective palladium-catalyzed oxidative cross-coupling of two allenes with the presence of a directing olefin in one of the allenes, enabling the facile synthesis of a broad range of functionalized [4]dendralenes in a convergent modular manner. Specifically, the selective allenic C-H activation of an allene with an allyl substituent as the assisting group gives rise to a vinylpalladium intermediate, which reacts with a less substituted allene in a carbopalladation, followed by a β-hydride elimination. The reaction sequence leads to a new C(sp2)-C(sp2) bond between two diene units. Remarkably, this protocol provides an unconventional strategy for the site-selective and stereoselective construction of C(vinyl)-C(vinyl) bonds without using any halogenated and organometallics olefin precursors. Furthermore, the practical transformations of the synthesized [4]dendralenes and late-stage modifications of biorelevant molecules demonstrate their potential in the total synthesis of natural products and drug discovery.