Pentagonal Rings Research Articles

Modification of cobalt bis(dicarbollide) ions with nitrile groups on carbon atoms: a unique low-temperature skeletal rearrangement due to the specific electron-donor character of CN substitution.

Herein, we report on the synthesis and stereochemistry of mono- and isomeric dinitrile derivatives of [(1,2-C2B9H11)2-3,3'-Co]- ions. The shape and electronic properties of CN groups can apparently surmount the strain associated with the substitution of two vicinal carbon positions. Owing to electron donation to the cage, this results in a substituent-induced rearrangement of one of the carbon atoms to the upper pentagonal ring. The molecular structure of this isomer was confirmed using sc-XRD and DFT chemical computations.

Nuclear Magnetic Resonance (NMR) and Density Functional Theory (DFT) Study of Water Clusters of Hydrogen-Rich Water (HRW)

The present study investigated the 1H Nuclear Magnetic Resonance (NMR) spectra of hydrogen-rich water (HRW) produced using the EVObooster device. The analyzed HRW has pH = 7.1 ± 0.11, oxidation–reduction potential (ORP) of (−450 ± 11) mV, and a dissolved hydrogen concentration of 1.2 ppm. The control sample was tap water filtered by patented technology. A 600 NMR spectrometer was used to measure NMR spectra. Isotropic 1H nuclear magnetic shielding constants of the most stable clusters (H2O)n with n from 3 to 28 have been calculated by employing the gauge-including-atomic-orbital (GIAO) method at the MPW1PW91/6-311+G(2d,p) density function level of theory (DFT). The HRW chemical shift is downfield (higher chemical shifts) due to increased hydrogen bonding. More extensive formations were formed in HRW than in control filtered tap water. The exchange of protons between water molecules is rapid in HRW, and the 1H NMR spectra are in fast exchange mode. Therefore, we averaged the calculated chemical shifts of the investigated water clusters. As the size of the clusters increases, the number of hydrogen bonds increases, which leads to an increase in the chemical shift. The dependence is an exponential saturation that occurs at about N = 10. The modeled clusters in HRW are structurally stabilized, suggesting well-ordered hydrogen bonds. In the article, different processes are described for the transport of water molecules and clusters. These processes are with aquaporins, fusion pores, gap-junction channels, and WAT FOUR model. The exponential trend of saturation shows the dynamics of water molecules in clusters. In our research, the chemical shift of 4.257 ppm indicates stable water clusters of 4–5 water molecules. The pentagonal rings in dodecahedron cage H3O+(H2O)20 allow for an optimal arrangement of hydrogen bonds that minimizes the potential energy.

Hydrogen Evolution Reactivity of Pentagonal Carbon Rings and p‐d Orbital Hybridization Effect with Ru

AbstractTopological defects are inevitable existence in carbon‐based frameworks, but their intrinsic electrocatalytic activity and mechanism remain under‐explored. Herein, the hydrogen evolution reaction (HER) of pentagonal carbon‐rings is probed by constructing pentagonal ring‐rich carbon (PRC), with optimized electronic structures and higher HER activity relative to common hexagonal carbon (HC). Furthermore, to improve the reactivity, we couple Ru clusters with PRC (Ru@PRC) through p‐d orbital hybridization between C and Ru atoms, which drives a shortcut transfer of electrons from Ru clusters to pentagonal rings. The electron‐deficient Ru species leads to a notable negative shift in d‐band centers of Ru and weakens their binding strength with hydrogen intermediates, thus enhancing the HER activity in different pH media. Especially, at a current density of 10 mA cm−2, PRC greatly reduces alkaline HER overpotentials from 540 to 380 mV. And Ru@PRC even exhibits low overpotentials of 28 and 275 mV to reach current densities of 10 and 1000 mA cm−2, respectively. Impressively, the mass activity and price activity of Ru@PRC are 7.83 and 15.7 times higher than that of Pt/C at the overpotential of 50 mV. Our data unveil the positive HER reactivity of pentagonal defects and good application prospects.

Non-alternant Benzodifluoranthene Tetraimides from 7,8,9,10-Fluoranthene Diimides: Synthesis, Structure, and Optical-Limiting Properties.

A novel tetraimide-functionalized non-alternant π-conjugated system, namely, benzodifluoranthene tetraimides (BDFTI), has been designed and synthesized through highly efficient UV-photocyclization of a vinyl-bridged fluoranthene diimide dimer (i.e., FDI-V). The synthesis of FDI-V starts from a straightforward three-step route to produce novel 7,8,9,10-fluoranthene diimide (FDIs) building-blocks, followed by nearly complete bromination and then Stille-coupling reaction to give the desired dimer. The analysis by X-ray crystallography confirms a near-coplanar geometry for FDIs, while BDFTI shows a U-shaped and distorted backbone configuration proven by theoretical optimizations. The tetraimide BDFTI exhibits several advantages over the FDI cores, including an extended absorption band and a red-shift in photoluminescence spectra. This enhancement can be attributed to the presence of additional electron-deficient imide units, which promotes increased intramolecular charge transfer and improved electron affinity. All the imides show a local aromatic characteristic owing to the incorporation of pentagon rings in the π-frameworks. The fully fused BDFTI exhibits nonlinear optical properties as analyzed by the open-aperture Z-scan technique, demonstrating superior optical-limiting performance compared to vinyl-bridged FDI-V. The versatile UV-photocyclization chemistries provide a pathway for developing complex and unique multiimide-functionalized π-conjugated systems, paving the way for creating high-performance optical-limiting materials.

Mechanical properties of TPDH-graphene: atomistic aspect

Abstract TPDH-graphene is a new type of two-dimensional carbon material predicted by first-principles calculations to have tetragonal (T), pentagonal (P), decagonal (D) and hexagonal (H) carbon ring structures. First-principles calculations show that this special structure gives it excellent mechanical properties and promising applications in nanoelectronics. In this paper, a comprehensive test of its mechanical properties was carried out using the classical molecular dynamics (MD), mainly exploring the effects of factors such as tensile direction and temperature on its mechanical properties, and exploring the effects of introducing rectangular and circular defects on its mechanical properties. The results show that: TPDH-graphene exhibits significant anisotropy in zigzag and armchair directions, and the material exhibits some tensile toughness in armchair direction; the mechanical properties of the material are weakened at higher temperatures; the adding of defects leads to the reduction of the mechanical properties of the material in different directions to different degrees, and the The tensile toughness in the armchair direction is weakened by the addition of defects.

Effect of Adding Phosphorus on Crystal Structure of W-V-Nb Complex Oxide and Catalytic Selective Oxidation of Acrolein.

The changes in the crystal structure of the W-V-Nb complex oxide with phosphorus addition to the hydrothermal synthesis process are investigated. The effect of the constituent units and crystal structure of phosphorus-added W-V-Nb complex oxide catalysts on the activity and selectivity for selective oxidation of acrolein is discussed. Phosphorus addition to the hydrothermal synthesis process promotes the formation of orthorhombic and trigonal W-V-Nb complex oxides. Orthorhombic and trigonal W-V-Nb complex oxide catalysts give higher acrylic acid selectivity in acrolein oxidation compared to poorly crystalline catalysts that only have {M6O21} pentagonal units and 7-membered rings.

Insight into the Reversible Hydrogen Storage of Titanium-Decorated Boron-Doped C20 Fullerene: A Theoretical Prediction

Hydrogen storage has been a bottleneck factor for the application of hydrogen energy. Hydrogen storage capacity for titanium-decorated boron-doped C20 fullerenes has been investigated using the density functional theory. Different boron-doped C20 fullerene absorbents are examined to avoid titanium atom clustering. According to our research, with three carbon atoms in the pentagonal ring replaced by boron atoms, the binding interaction between the Ti atom and C20 fullerene is stronger than the cohesive energy of titanium. The calculated results revealed that one Ti atom can reversibly adsorb four H2 molecules with an average adsorption energy of −1.52 eV and an average desorption temperature of 522.5 K. The stability of the best absorbent structure with a gravimetric density of 4.68 wt% has been confirmed by ab initio molecular dynamics simulations. These findings suggest that titanium-decorated boron-doped C20 fullerenes could be considered as a potential candidate for hydrogen storage devices.

Thermal pyrolysis behavior and mechanisms of kraft lignin using methane, H2, and H2O as reactive medium: A ReaxFF molecular dynamics simulation

Biomass has become an alternative to fossil fuels due to its capacity to provide carbon-neutral energy. However, the conversion of kraft lignin into high-value chemicals remains challenging. Hydrotreatment, utilizing CH4, H2, or H2O, enables the production of high-quality liquid hydrocarbon fuels while enhancing hydrogen utilization. Reactive molecular dynamics was employed to investigate the influence of CH4, H2, and H2O as reactive medium of kraft lignin at the atomic scale. The three reactive mediums increased the maximum heavy tar yield by 8.34%, 8.07%, and 8.53% respectively, and increased the hydrogen content of pyrolysis products. Steam conditions promote the decomposition of ether bonds, while H2 and CH4 exhibit stronger inhibitory on the decomposition of carbon hexagonal rings. A crucial role of pentagonal carbon rings as intermediates in the lignin cracking process was found. These findings provide valuable insights for optimizing the pyrolysis conditions of kraft lignin to achieve the desired product yields.

A Dual CQD-Catalysis and H-Bond Acceptor for Controlling Product Selectivity and Regioselectivity in Symmetric/Unsymmetric Azoxy Arenes.

Azoxy arenes are valuable compounds in different areas of chemistry, such as organic chemistry, medicinal chemistry, and natural product chemistry. Despite their value, the regioselective synthesis of unsymmetric azoxybenzenes has remained a real challenge in the field. Herein, the product selectivity in oxidative homocoupling of anilines into symmetric azoxybenzenes was first achieved by an asparagine-functionalized CQD catalyst. Subsequently, in the cross-coupling of anilines into the unsymmetric azoxybenzenes via an ortho H-bond acceptor (HBA) on one of the coupling anilines, the regioselectivity was effectively controlled. It was demonstrated that ortho-HBA could mechanistically establish a six-membered intramolecular hydrogen-bonded ring on an N,N'-dihydroxy intermediate. The formed hydrogen bond makes the nearby nitrogen eminently suitable for the slow dehydration step. As a result, the functional oxygen of the azoxy compound is placed far from the HBA. The o-HBA mechanism also controls the regioselectivity ratio in which 1:0 (with an intramolecular H-bonded hexagonal ring), 2:1 (with an intramolecular H-bonded pentagonal ring), and 1:1 (without an ortho-HBA) isomeric mixtures could be achieved. The HBA mechanism was exploited by different substituted anilines, and various unsymmetric azoxybenzenes were synthesized. Finally, with the aid of mechanistic studies, a plausible mechanism for the reaction was proposed.

Hydrogen Evolution Reactivity of Pentagonal Carbon Rings and p-d Orbital Hybridization Effect with Ru.

Topological defects are inevitable existence in carbon-based frameworks, but their intrinsic electrocatalytic activity and mechanism remain under-explored. Herein, the hydrogen evolution reaction (HER) of pentagonal carbon-rings is probed by constructing pentagonal ring-rich carbon (PRC), with optimized electronic structures and higher HER activity relative to common hexagonal carbon (HC). Furthermore, to improve the reactivity, we couple Ru clusters with PRC (Ru@PRC) through p-d orbital hybridization between C and Ru atoms, which drives a shortcut transfer of electrons from Ru clusters to pentagonal rings. The electron-deficient Ru species leads to a notable negative shift in d-band centers of Ru and weakens their binding strength with hydrogen intermediates, thus enhancing the HER activity in different pH media. Especially, at a current density of 10 mA cm-2, PRC greatly reduces alkaline HER overpotentials from 540 to 380 mV. And Ru@PRC even exhibits low overpotentials of 28 and 275 mV to reach current densities of 10 and 1000 mA cm-2, respectively. Impressively, the mass activity and price activity of Ru@PRC are 7.83 and 15.7 times higher than that of Pt/C at the overpotential of 50 mV. Our data unveil the positive HER reactivity of pentagonal defects and good application prospects.

Superconductivity in Monolayer Carbon Allotropes with High Thermal Stability.

Intrinsic superconductivity is rarely discovered in sp2-hybridized monolayer carbon allotropes. Here we design a carbon monolayer configured of pentagon, heptagon, and hexagon rings with p2 plane group symmetry. Full-sp2 hybridization is proposed to favor thermal metastability on a low Gibbs free energy. The extremely small thermal expansion coefficient is predicted to the turn negative value to positive with elevating temperature. Carbon polygon structures remain intact at a high thermal temperature of 3,000 K. The high specific surface area is found to approach 2,700 m2/g, with O2-adsorption being advantageous over pristine graphene. We reveal electronic Fermi surfaces mediated by phonon modes of carbon out-of-plane vibrations. By calculating the Eliashberg equation, we evaluate intrinsic superconductivity with a large electron-phonon coupling coefficient. The superconducting transition temperature is estimated to reach 20 K under a high logarithmic average frequency. These first-principles calculations shall stimulate experimentalists' interest in exploring low-dimensional carbon superconductors with gas sensitivity.

Hexa-Penta nanobelt: a novel stable structure with potential optical application

ABSTRACT We report a theoretical investigation of a new carbon nanobelt called Hexa-Penta-belt with molecular formula C 42 H 18 . Hexa-Penta-belt is a variation of the synthesised Methylene-bridged[6]cycloparaphenylene (M-b[6]CPP) with molecular formula C 42 H 24 . Hexa-Penta-belt consists of carbon pentagon and hexagon rings and was inspired by the Penta-belt (theoretically derived from the penta-graphene sheet), the [12]cyclophenacene, and the M-b[6]CPP synthesised by Itami and Segawa [1]. Using Density Functional Theory (DFT), we calculated Hexa-Penta-belt electronic, optical, and thermodynamic properties and their vibrational frequencies. Hexa-Penta-belt is a structurally and thermally stable molecule, as Quantum Molecular Dynamics (QMD) showed. The results exhibited that the Hexa-Penta-belt has excellent electronic stability comparable to C 60 , and it behaves as a semiconductor with a gap estimated at 0.89 eV. It absorbs in the ultraviolet and the visible region (corresponding to the violet, green, and red colours) presenting an absorption more consistent in the visible region than M-b[6]CPP, which could indicate application, for example, as an optical nanosensor. We verified through the carbon atom binding energy that Hexa-Penta-belt is an intermediate molecule between Penta-belt and [12]cyclophenacene.

Co incorporated pentagraphene as an efficient single-atom catalyst for reduction of CO2: First-principles investigations

Hydrogenation of carbon dioxide (CO2) to formic acid is explored through density functional theory calculations over Co decorated penta-graphene (Co@PG) as single atom catalyst (SAC). Co is successfully stabilized over pentagraphene due to strong overlapping of Co-3d and C-2p states of pentagonal ring of pentagraphene near fermi level. The higher diffusion barrier for Co over pentagraphene evince that the clustering of Co atom is restricted. This suggests that Co@PG can be used as a catalyst for reducing CO2. Moreover, the Hirshfeld charge density, molecular electrostatic potential and spin density analysis indicates that the Co site is the highly active site for CO2 hydrogenation reaction. Both CO2 and H2 show strong interaction with Co@PG. In co-adsorbed state, the interactions are even larger due to greater mutual polarization of reactants and localization of positive charge on Co with adsorption energy of -2.57 eV. The hydrogenation can proceed at ambient temperature due to a small energy barrier of 0.29 eV, the competitive reaction i.e. CO hydrogenation with CO2 hydrogenations almost impossible over the catalyst surface due to larger energy barriers i.e. 1.98 eV. Thus, this work shows that Co@PG can be used as an efficient and promising catalyst for CO2 hydrogenation at room temperature.

Exploring the Surface Stability of Non-Benzenoid and Non-Planar High-Membered Rings

The synthesis of carbon-based nanomaterials has experienced an enormous advance in the last 15 years, in part motivated by the advent of On-surface Synthesis (OSS).1 This young field, based on the synthesis of carbon-based nanostructures directly on surfaces thanks to their unique catalytic properties, has allowed the formation of otherwise unattainable extended pi-conjugated systems, like atomically precise graphene nanoribbons,which turned out to be an excellent workbench to explore new physico-chemical properties at the atomic and molecular level.2 Once it was shown the feasibility to use this bottom-up approach to induce organic chemical reactions between tailored precursor monomers, the field evolved toward adding increasing complexity to the final products, either by modifying the dimensionality, edge structure and shape or by including heteroatoms or defects. All these approaches resulted in new intriguing properties as modified band structures or topological states. Of particular recent interest is the effect of non-benzenoid rings in the emergence of pi-magnetism, so far mainly focused on pentagonal rings.3 However, if we want to increase the versatility of the field and explore new possible functionalities associated to the presence of non-benzenoid rings in the nanostructures, it is mandatory to study their stability on surfaces.In this talk, we will discuss the thermal stability of different high-membered non-benzenoid rings, specifically heptagons and octogons, when included into graphene-based nanostructures, paying special attention to the reaction mechanisms involved. References (1) Gourdon, A. On-Surface Covalent Coupling in Ultrahigh Vacuum. Angew. Chem. Int. Ed. 2008, 47 (37), 6950–6953. https://doi.org/10.1002/anie.200802229.(2) Clair, S.; de Oteyza, D. G. Controlling a Chemical Coupling Reaction on a Surface: Tools and Strategies for On-Surface Synthesis. Chem. Rev. 2019, 119 (7), 4717–4776. https://doi.org/10.1021/acs.chemrev.8b00601.(3) Oteyza, D. G. de; Frederiksen, T. Carbon-Based Nanostructures as a Versatile Platform for Tunable π-Magnetism. J. Phys. Condens. Matter 2022, 34 (44), 443001. https://doi.org/10.1088/1361-648X/ac8a7f.

DFT investigation on the design and optimization of icosahedral and octahedral beryllium nitride (Be3N2)x fullerene analogue. A comparative study with isosymmetry carbon fullerene

In this contribution, based on density Functional Theory, we focus on studying the structural and dynamic stability of octahedral and icosahedral beryllium nitride (Be3N2)x fullerenes and their symmetry equivalent carbon molecules. The icosahedron structure of beryllium nitride and carbon-based fullerenes shows hybrid features, between a sphere and a polyhedron. Nevertheless, the cohesive energies of carbon fullerenes are slightly lower than those of beryllium nitride based on Be3N2 units. Although icosahedral Ih (1,1) and Ih (2,2) (Be3N2)30 and (Be3N2)120 are energetically slightly less favorable than their corresponding carbon fullerenes, they showed chemically stable structures. IR & Raman spectra are also simulated using a coupled-perturbed KS/HF scheme permitting their identification. Importantly, no imaginary frequency is recorded in their vibrational spectra which confirms an inherent dynamic stability. These results provide valuable insights that can be extrapolated to other noncarbon nanostructures containing pentagonal rings or pentagonal defects.

Ring Fusion Elevates the Electronic Mobility of Azabenzannulated Perylene Diimide.

The backwardness of n-type organic semiconductors still exists compared with the p-type counterparts. Thus, the development of high-performance n-type organic semiconductors is of great importance for organic electronic devices and their integrated circuits. In recent years, azabenzannulated perylene diimide (PDI), as one of immense bay-region-annulated PDI derivatives, has drawn considerable attentions. However, the electronic mobilities of azabenzannulated PDI derivatives are barely satisfactory. In this contribution, the peripheral benzene ring in azabenzannulated PDI 2 was fused to the ortho position by intramolecular C-H arylation cyclization. This endows the resultant azabenzannulated PDI 4 a planar configuration as well as electron deficient pentagonal ring. As a result, the electronic mobility of 4 is almost two orders of magnitude higher than that of the nonfused azabenzannulated PDI 2. This work shall pave a new avenue in elevating the performance of azabenzannulated PDI in organic electronics.

A novel and promising Penta-Octa-Based silicon carbide semiconductor

Penta-octa-graphene (POG) consists of pentagonal and octagonal carbon rings, hosting type-I and type-II Dirac line nodes due to its sp2 and sp3 mixed bonds. Inorganic analogs of 2D carbon lattices have increased the potential applications and changed the main properties of carbon-based structures. Therefore, this work proposes penta-octa-graphene based on silicon carbide using DFT simulations. With a cohesive energy of −5.22 eV/atom, POG-Si5C4 is energetically viable in comparison with other silicon carbide-based monolayers. Phonon dispersion analysis confirms the POG-Si5C4 dynamical stability. MD simulations demonstrate that this new monolayer can withstand temperatures up to 1020 K. Electronic analysis indicates it is a semiconductor with an indirect band gap transition of 2.02 eV. The mechanical properties exhibit anisotropy, with Young’s modulus ranging from 38.65 to 99.47 N/m and an unusual negative Poisson’s ratio of −0.09. The band edge alignment suggests that POG-Si5C4 holds potential for hydrogen generation through photocatalytic water splitting. This research opens possibilities for designing inorganic penta-octa-based structures and provides insights for future experimental and theoretical studies focused on exploring and optimizing advanced silicon-carbide 2D materials.

Towards the Tetrabenzo-Fused Circumazulene via In-Solution and On-Surface Synthesis

The synthesis of circumazulene, a nonalternant isomer of circumnaphthalene, and its π-expanded derivatives poses a considerable challenge due to the lack of a suitable synthetic strategy. In this work, we present our efforts toward achieving tetrabenzo-fused circumazulene (1) through both solution and on-surface syntheses. In the case of in-solution synthesis, we obtained a product (P) with the desired target mass, but the structural verification proved to be challenging owing to the presence of various structural isomers. In the on-surface synthesis approach, a series of unexpected azulene-embedded nanographenes were obtained, including a molecule with an additional pentagonal ring (U1) based on the backbone of 1. Furthermore, theoretical calculations were conducted to shed light on these unexpected structures and to investigate their aromaticity. This work opens a new avenue for the design and synthesis of novel nonalternant graphene nanostructures incorporating circumarene.

Stable Pentagonal Layered Palladium Diselenide Enables Rapid Electrosynthesis of Hydrogen Peroxide.

Electrosynthesis of hydrogen peroxide (H2O2) via the two-electron oxygen reduction reaction (2e- ORR) is promising for various practical applications, such as wastewater treatment. However, few electrocatalysts are active and selective for 2e- ORR yet are also resistant to catalyst leaching under realistic operating conditions. Here, a joint experimental and computational study reveals active and stable 2e- ORR catalysis in neutral media over layered PdSe2 with a unique pentagonal puckered ring structure type. Computations predict active and selective 2e- ORR on the basal plane and edge of PdSe2, but with distinct kinetic behaviors. Electrochemical measurements of hydrothermally synthesized PdSe2 nanoplates show a higher 2e- ORR activity than other Pd-Se compounds (Pd4Se and Pd17Se15). PdSe2 on a gas diffusion electrode can rapidly accumulate H2O2 in buffered neutral solution under a high current density. The electrochemical stability of PdSe2 is further confirmed by long device operational stability, elemental analysis of the catalyst and electrolyte, and synchrotron X-ray absorption spectroscopy. This work establishes a new efficient and stable 2e- ORR catalyst at practical current densities and opens catalyst designs utilizing the unique layered pentagonal structure motif.

Evolution from Topological Nodal Points to Nodal Line: Realized in Fused Carbon Allotrope

Herein, via first‐principle calculations and theoretical analysis, a new Dirac semimetal carbon system called C32, which is composed of pentagonal, hexagonal, heptagonal, and octagonal carbon rings is systematically investigated. The stability of C32 is verified by calculating the phonon dispersion, elastic constants, etc., and an appropriate pathway for experimental synthesis is proposed. Besides, it is discovered that the system holds the quadruple rotation and inversion symmetry, resulting in the emergence of eight twisted Dirac cones (D1 and D2) with a highly anisotropic Fermi velocity from 3.83 × 105 to 8.96 × 105 m s−1 along different k directions. To substantiate the semimetallic nature of C32, its nontrivial topological properties are confirmed through the presence of topologically protected edge states, and the nonzero ℤ2 topological invariant. More importantly, by introducing biaxial strain, it is uncovered that Dirac cones can gradually evolve into a nodal line, and the perfect nodal line can be obtained when the biaxial strain is 13.3%. Furthermore, by constructing the tight‐binding model, the appearance of the Dirac cone is perfectly repeated and its evolution into the nodal line under biaxial strain is explained.