Pentagonal Rings Research Articles

Indenoannulated Tridecacyclene: An All-Carbon Seven-Stage Redox-Amphoter.

We disclose an indenoannulated tridecacyclene comprising a central cyclooctatetraene moiety with multiple adjacent pentagonal rings which is accessible in a concise synthetic sequence. The saddle-shaped geometry of the non-benzenoid polycyclic scaffold and its unique packing behavior in the solid state were characterized by X-ray crystallography. In electrochemical studies, the compound undergoes seven reversible redox events comprising five reductions and two oxidations. The dicationic and dianionic species obtained by chemical oxidation and reduction, respectively, were characterized spectroscopically in solution. Density functional theory calculations were applied to provide insights into aromaticity evolution in the respective charged species, highlighting the beneficial effect of the non-benzenoid moieties on charge stabilization.

Formation of Nitrogen-Doped Positively Curved Molecules by π-Extension.

Two nitrogen-doped positively curved aromatic molecules bearing doubly fused pentagonal rings were synthesized and characterized. Crystallographic analysis confirms the formation of a bowl-shaped structure, which is induced by the fusion of adjacent pentagons to the rigid aromatic planes. Both compounds demonstrate good photoluminescence. These electron-rich bowl-shaped molecules can associate with C60 to form complexes in 2:1 ratio in toluene with different association constants depending on the molecular dimension of the hosts.

Post-Formation of Fused Pentagonal Structure on Fjord Region of Polyaromatic Hydrocarbons under Hydrothermal Conditions.

This study explores the synthesis of cyclopenta-fused polyaromatic hydrocarbons (CP-PAHs) via Pt-catalyzed cyclization in water, focusing on the formation of fused pentagonal rings within heavily fused PAH frameworks. Utilizing platinum catalysts at lower temperatures (200-260 °C) in water, led to the successful synthesis of singly cyclized CP-PAHs. The reaction conditions facilitated the mono-cyclization of substrates such as dibenzo[g,p]chrysene and its isomers, yielding the desired products while suppressing the formation of bis-cyclized compounds. The use of Fe2O3 as an additive in conjunction with PtO2 was effective to suppress hydrogenation of the substrates and products. The products exhibited a redshift in UV-visible absorption and photoluminescence bands due to a decrease in the HOMO-LUMO energy gap. These findings highlight the potential of Pt-catalyzed cyclization for the controlled synthesis of CP-PAHs, with implications for various applications in materials science.

Non-Templated Assembly of D5h-Symmetric Pd5L10 Rings by Precise Ligand Angle Adjustment.

We report a series of Pd(II)nL2n coordination rings for which nuclearity is controlled by the binding angle of the corresponding bis-monodentate bridging ligands. Judicious choice of the angle within a family of rather rigid ligands allowed for the first-time to synthesize a homoleptic five-membered Pd5L10 ring that does not require any template to form. We demonstrate that control over the ring size is maintained both in the solid-, solution-, and gas-phase. Two X-ray structures of five-membered rings from ligands with ideal angles (yielding a perfect pentagonal ring) vs. suboptimal angles (resulting in a highly distorted structure) illustrate the importance of the correct ligand geometry. A mathematical model for estimating the expected ring size based on the ligand angle was derived and DFT computations show that ring-strain is the major factor determining the assembly outcome.

Review of: "C70 Fullerenes Closed hollow cages are made of interconnected carbon atoms in pentagonal and hexagonal rings with a cage-like melted ring structure that resembles a rugby ball"

Review of: "C70 Fullerenes Closed hollow cages are made of interconnected carbon atoms in pentagonal and hexagonal rings with a cage-like melted ring structure that resembles a rugby ball"

Review of: "C70 Fullerenes Closed hollow cages are made of interconnected carbon atoms in pentagonal and hexagonal rings with a cage-like melted ring structure that resembles a rugby ball"

Review of: "C70 Fullerenes Closed hollow cages are made of interconnected carbon atoms in pentagonal and hexagonal rings with a cage-like melted ring structure that resembles a rugby ball"

Improving stability, mechanical and electronic properties of pentadiamond by doping with alkali or alkaline-earth metals: A first-principles investigation

Pentadiamond (PD), a recently proposed carbon allotrope, has garnered considerable attention owing to its unique covalent framework comprising both sp2 and sp3 carbon atoms. Despite its intriguing structure with potentially useful thermal, electronic and optical properties, PD is supposed to be thermodynamically very unstable, due to the strain imposed by adjacent pentagonal rings in the carbon framework, which poses a major concern for its practical production. Here, we employ first-principles simulations to demonstrate that inserting alkali or alkaline-earth metals into the bigger cavities of PD significantly enhances its thermodynamic stability. Moreover, the resulting doped materials exhibit high kinetic stability at high temperatures typical for synthesis of fullerenes and metallofullerenes. We systematically investigate the structures and the modulation of mechanical properties and electronic structures of metal-doped PDs. Most remarkably, beryllium is revealed to be the energetically most favorable dopant among the metals considered. Be-doped PD exhibits an increased shear and Young's moduli (by about 55.6 % and 44.4 %, respectively), along with a substantially reduced Poisson's ratio (from 0.23 to 0.14). Furthermore, doping with Be transforms PD from an indirect-gap material to a direct-gap semiconductor, narrowing the band gap from 3.58 eV to 2.67 eV. We hope these findings may stimulate the experimental endeavors to synthesize metal-doped PD materials and unlock their potential applications.

Topological Structure Realized in Cove-Edged Graphene Nanoribbons via Incorporation of Periodic Pentagon Rings.

Cove-edged zigzag graphene nanoribbons are predicted to show metallic, topological, or trivial semiconducting band structures, which are precisely determined by their cove offset positions at both edges as well as the ribbon width. However, due to the challenge of introducing coves into zigzag-edged graphene nanoribbons, only a few cove-edged graphene nanoribbons with trivial semiconducting bandgaps have been realized experimentally. Here, we report that the topological band structure can be realized in cove-edged graphene nanoribbons by embedding periodic pentagon rings on the cove edges through on-surface synthesis. Upon noncontact atomic force microscopy and scanning tunneling spectroscopy measurements, the chemical and electronic structures of cove-edged graphene nanoribbons with periodic pentagon rings have been characterized for different lengths. Combined with theoretical calculations, we find that upon inducing periodic pentagon rings the cove-edged graphene nanoribbons exhibit nontrivial topological structures. Our results provide insights for the design and understanding of the topological character in cove-edged graphene nanoribbons.

On-Surface Synthesis of Non-Benzenoid Nanographenes Embedding Azulene and Stone-Wales Topologies.

The incorporation of non-benzenoid motifs in graphene nanostructures significantly impacts their properties, making them attractive for applications in carbon-based electronics. However, understanding how specific non-benzenoid structures influence their properties remains limited, and further investigations are needed to fully comprehend their implications. Here, we report an on-surface synthetic strategy toward fabricating non-benzenoid nanographenes containing different combinations of pentagonal and heptagonal rings. Their structure and electronic properties were investigated via scanning tunneling microscopy and spectroscopy, complemented by computational investigations. After thermal activation of the precursor P on the Au(111) surface, we detected two major nanographene products. Nanographene Aa-a embeds two azulene units formed through oxidative ring-closure of methyl substituents, while Aa-s contains one azulene unit and one Stone-Wales defect, formed by the combination of oxidative ring-closure and skeletal ring-rearrangement reactions. Aa-a exhibits an antiferromagnetic ground state with the highest magnetic exchange coupling reported up to date for a non-benzenoid containing nanographene, coexisting with side-products with closed shell configurations resulted from the combination of ring-closure and ring-rearragement reactions (Ba-a , Ba-s , Bs-a and Bs-s ). Our results provide insights into the single gold atom assisted synthesis of novel NGs containing non-benzenoid motifs and their tailored electronic/magnetic properties.

On‐Surface Synthesis of Non‐Benzenoid Nanographenes Embedding Azulene and Stone‐Wales Topologies

AbstractThe incorporation of non‐benzenoid motifs in graphene nanostructures significantly impacts their properties, making them attractive for applications in carbon‐based electronics. However, understanding how specific non‐benzenoid structures influence their properties remains limited, and further investigations are needed to fully comprehend their implications. Here, we report an on‐surface synthetic strategy toward fabricating non‐benzenoid nanographenes containing different combinations of pentagonal and heptagonal rings. Their structure and electronic properties were investigated via scanning tunneling microscopy and spectroscopy, complemented by computational investigations. After thermal activation of the precursor P on the Au(111) surface, we detected two major nanographene products. Nanographene Aa−a embeds two azulene units formed through oxidative ring‐closure of methyl substituents, while Aa−s contains one azulene unit and one Stone‐Wales defect, formed by the combination of oxidative ring‐closure and skeletal ring‐rearrangement reactions. Aa−a exhibits an antiferromagnetic ground state with the highest magnetic exchange coupling reported up to date for a non‐benzenoid containing nanographene, coexisting with side‐products with closed shell configurations resulted from the combination of ring‐closure and ring‐rearragement reactions (Ba−a, Ba−s, Bs‐a and Bs−s). Our results provide insights into the single gold atom assisted synthesis of novel NGs containing non‐benzenoid motifs and their tailored electronic/magnetic properties.

Molecular simulation study on carbon dioxide replacement in methane hydrate near the freezing point

Carbon dioxide (CO2) replacement method for hydrate extraction offers advantages such as resource utilization, greenhouse gas reduction, carbon sequestration, geological stability and controllability. The enhancement of CO2 replacement efficiency for methane hydrates and the achievement of more efficient hydrate extraction have consistently been the primary focus of researchers. In this work, we explored the CO2 replacement process in methane hydrates at different temperatures above the methane hydrate phase equilibrium line using molecular simulations. The results demonstrate that the replacement process of CO2 for methane hydrates occurred spontaneously even within the equilibrium region of methane hydrates. The CO2 replacement of methane molecules in hydrates can be divided into three steps: intrusion of CO2 molecules into the semi-cage structures, methane hydrates decomposition and CO2 hydrates formation. The decomposition of methane hydrates plays a crucial role in determining the replacement process. Moreover, the replacement process was significantly affected by temperature, and CO2 showed the highest replacement efficiency at 272 K. At this temperature, CO2 molecules exhibited higher activity, rendering them more likely to disrupt the pentagonal or hexagonal ring structures of the methane hydrate cages. Our simulation results provide microscopic insights into the carbon dioxide replacement in methane hydrate below and above the freezing point.

Aromatic and magnetic properties in a series of heavy rare earth-doped Ge6 cluster anions.

A series of pentagonal bipyramidal anionic germanium clusters doped with heavy rare earth elements, (RE = Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu), have been identified at the PBE0/def2-TZVP level using density functional theory (DFT). Our findings reveal that the centrally doped pentagonal ring structure demonstrates enhanced stability and heightened aromaticity due to its uniform bonding characteristics and a larger charge transfer region. Through natural population analysis and spin density diagrams, we observed a monotonic decrease in the magnetic moment from Gd to Yb. This is attributed to the decreasing number of unpaired electrons in the 4f orbitals of the heavy rare earth atoms. Interestingly, the system doped with Er atoms showed lower stability and anti-aromaticity, likely due to the involvement of the 4f orbitals in bonding. Conversely, the systems doped with Gd and Tb atoms stood out for their high magnetism and stability, making them potential building blocks for rare earth-doped semiconductor materials.

Exploring aromatic rings with planar tetracoordinate group 13-15 atoms.

This study examines systems containing planar tetracoordinate group 13-15 atoms (E) within pentagonal C4H2E rings bridged by Si or Ge atoms. A detailed chemical bonding analysis of eleven candidates shows that true tetracoordination is achieved only in the C4H2NGe2+ system.

Photofragmentation of corannulene (C20H10) and sumanene (C21H12) cations in the gas phase and their astrophysical implications.

Aromatic infrared bands (AIBs) dominate the mid-infrared spectra of many galactic and extragalactic sources. These AIBs are generally attributed to fluorescence emission from aromatic molecules. Unified efforts from experimentalists and theoreticians to assign these AIB features have recently received additional impetus with the launch of the James Webb Space Telescope (JWST) as the Mid-InfraRed Instrument (MIRI) delivers a mid-IR spectrum with greatly increased sensitivity and spectral resolution. PAHs in space can exist in either neutral or ionic form, absorb UV photons and undergo fragmentation, becoming a rich source of small hydrocarbons. This top-down mechanism of larger PAHs fragmenting into smaller species is of utmost importance in photo-dissociation regions (PDR) in space. In this work, we experimentally and theoretically investigate the photo-fragmentation pathways of two astronomically significant PAH cations - corannulene (C20H10) and sumanene (C21H12), which are structural motifs of fullerene C60, to understand their sequential fragmentation pathways. The photo-fragmentation experiments exhibit channels that are significantly different from planar PAHs. The breakdown of the carbon skeleton is found to follow different pathways for C20H10 and C21H12 because of the number and positioning of pentagon rings, yet the most abundant low mass cations produced by these two species are found to be similar. The low mass cations showcased in this work could be of interest due to their possible astronomical detections. For completeness, the qualitative photofragmentation behaviour of dicationic corannulene and sumanene has also been investigated, but the potential energy surface of these dications is beyond the scope of this paper.

Diradicaloid Boron‐Doped Molecular Carbons Achieved by Pentagon‐Fusion

AbstractMolecular carbons (MCs) are molecular cutouts of carbon materials. Doping with heteroatoms and constructing open‐shell structures are two powerful approaches to achieve unexpected and unique properties of MCs. Herein, we disclose a new strategy to design open‐shell boron‐doped MCs (BMCs), namely by pentagon‐fusion of an organoborane π‐system. We synthesized two diradicaloid BMC molecules that feature C24B and C38B π‐skeletons containing a pentagonal ring. A thorough investigation reveals that such pentagon‐fusion not only leads to their local antiaromaticity, but also incorporates an internal quinoidal substructure and thereby induces open‐shell singlet diradical states. Moreover, their fully fused structures enable efficient π conjugation, which is expanded over the whole frameworks. Consequently, some intriguing physical properties are achieved, such as narrow energy gaps, very broad light absorptions, and superior photothermal capability, along with excellent photostability. Notably, the solid of the C38B molecule exhibits absorption that covers the range of 300–1200 nm and an efficiency of 93.5 % for solar‐driven water evaporation, thus demonstrating the potential of diradicaloid BMCs as high‐performance organic photothermal materials.

Diradicaloid Boron‐Doped Molecular Carbons Achieved by Pentagon‐Fusion

AbstractMolecular carbons (MCs) are molecular cutouts of carbon materials. Doping with heteroatoms and constructing open‐shell structures are two powerful approaches to achieve unexpected and unique properties of MCs. Herein, we disclose a new strategy to design open‐shell boron‐doped MCs (BMCs), namely by pentagon‐fusion of an organoborane π‐system. We synthesized two diradicaloid BMC molecules that feature C24B and C38B π‐skeletons containing a pentagonal ring. A thorough investigation reveals that such pentagon‐fusion not only leads to their local antiaromaticity, but also incorporates an internal quinoidal substructure and thereby induces open‐shell singlet diradical states. Moreover, their fully fused structures enable efficient π conjugation, which is expanded over the whole frameworks. Consequently, some intriguing physical properties are achieved, such as narrow energy gaps, very broad light absorptions, and superior photothermal capability, along with excellent photostability. Notably, the solid of the C38B molecule exhibits absorption that covers the range of 300–1200 nm and an efficiency of 93.5 % for solar‐driven water evaporation, thus demonstrating the potential of diradicaloid BMCs as high‐performance organic photothermal materials.

The impact of lead on structural, electronic, and vibrational properties of pristine C36 and its boron, nitrogen-dopant C36 on pentagonal and hexagonal rings

In this work, lead's impacts on the structural, electronic, and vibrational characteristics of pure C36 and C36 doped with boron and nitrogen on pentagonal and hexagonal rings are calculated using the DFT method. We provide an in-depth examination of these characteristics and how lead affects them. The adsorption energy, the highest occupied molecular orbital (HOMO), the lowest unoccupied molecular orbital (LUMO), and electrostatic potentials at the isosurface (EPI) have been studied in detail. Assess the ring dependence of the lead adsorption energy for the hexagonal and pentagonal rings of pristine C36 and B and N impurities at the substitutional site. The adsorption energy for the Pb on pristine C36 is endothermic; however, it is exothermic for the Pb on NB-doped C36 but has different values on the pentagonal and hexagonal rings. The results demonstrate that nitrogen and boron doping significantly increased the Pb atom's adsorption energy when the dopants occupied pentagonal sites. In addition, the bond lengths surrounding the impurity and the bond lengths of Pb atoms placed on pristine C36, BN-doped hexagonal ring, and BN-doped pentagonal ring in C36 are investigated. The electrostatic potential isosurface (EPI) surrounding the BN-doped hexagonal and pentagonal rings of C36 is described. The Mulliken charge transfer analysis demonstrates that the interaction between NB-doped C36 fullerene and lead (Pb) has a substantial effect on the charge transfer process and the reactivity of the doped system towards lead. However, the quantity of charge transmitted depends on the impurity's location on the hexagonal and pentagonal rings. These findings aid in the atomistic understanding of the interaction between a single Pb atom on the surface of C36 and BN-doped C36 at various rings. Our findings not only shed light on the complex interplay between lead and C36 but also offer valuable insights into potential applications in materials engineering and environmental remediation.

On‐Surface Interchain Coupling and Skeletal Rearrangement of Indenofluorene Polymers

AbstractOn‐surface synthesis serves as a powerful approach to construct π‐conjugated carbon nanostructures that are not accessible by conventional wet chemistry. Nevertheless, this method has been limited by the types and numbers of available on‐surface transformations. While the majority of successful cases exploit thermally triggered dehalogenative carbon–carbon coupling and cyclodehydrogenation, rearrangement of appropriate functional moieties has received limited research attention. Here, the unprecedented interchain coupling and thermally induced skeleton rearrangement are described of (dihydro)indeno[2,1‐b]fluorene (IF) polymers on an Au(111) surface under ultrahigh vacuum conditions, leading to different ladder polymers as well as fully fused graphene nanoribbon segments containing pentagonal and heptagonal rings. Au‐coordinated nanoribbons are also observed. All structures are unambiguously characterized by high‐resolution scanning probe microscopy. The current results provide an avenue to fabricating a wider variety of π‐conjugated polymers and carbon nanostructures comprising nonhexagonal rings as well as rarely explored organometallic nanoribbons.

Ductile behavior of a penta-boron nitride nanosheet triggered by structure transition for enhancing hydrogels

Boron nitride nanosheet (BNNS) is an attractive nanomaterial to improve polymeric materials in hydrogels due to their high mechanical properties, robust interfacial properties with polymer, and non-toxicity. However, the mismatching deformation capacity between BNNS and hydrogels results in damage to the BNNS-hydrogels interface and deteriorates the tensile properties of BNNS reinforced hydrogels. By adopting nanotechnology, the brittle nature of BNNSs can be modified. A novel penta-BNNS exhibits pentagonal rings, presenting ductile behavior under tensile deformation. The tensile test is performed by molecular dynamics simulations. The simulation results show that the ultimate failure strain of the penta-BNNS is significantly increased, which is attributed to the structure transition of the pentagonal rings in the penta-BNNS under tensile deformation. Due to the structure transition, the deformation capacity of the penta-BNNS is significantly improved with respect to the hexa-BNNS. This study links the structure to ductile behavior, which helps to devise advanced two-dimensional nanomaterials for improving hydrogels.

Examining O[Formula: see text] adsorption on pristine and defective popgraphene sheets: A DFT study.

Popgraphene (PopG) is a two-dimensional carbon-based material with fused pentagonal and octagonal rings. Like graphene, it exhibits a metallic band gap and exceptional thermal, dynamic, and mechanical stability. Here, we theoretically study the electronic and structural properties of PopG monolayers, including their doped and vacancy-endowed versions, as O[Formula: see text] adsorbers. Our findings show that pristine and vacancy-endowed PopG sheets have a comparable ability to adsorb O[Formula: see text] molecules, with adsorption energies ranging from [Formula: see text]0.57 to [Formula: see text]0.59 eV (physisorption). In these cases, octagonal rings play a dominant role in the adsorption mechanism. Platinum and Silicon doping enhance the O[Formula: see text] adsorption in areas close to the octagonal rings, resulting in adsorption energies ranging from [Formula: see text]1.13 to [Formula: see text]2.56 eV (chemisorption). Furthermore, we computed the recovery time for the adsorbed O[Formula: see text] molecules. The results suggest that PopG/O[Formula: see text] interaction in pristine and vacancy-endowed cases can change the PopG electronic properties before O[Formula: see text] diffusion. Density Functional Theory (DFT) simulations, with Van der Waals corrections (DFT-D, within the Grimme scheme), were performed to study the structural and electronic properties of PopG/O[Formula: see text] systems using the DMol3 code within the Biovia Materials Studio software. The exchange and correlation functions are treated within the generalized gradient approximation (GGA) as parameterized by Perdew-Burke-Ernzerhof (PBE) functional. We used the double-zeta plus polarization (DZP) for the basis set in these cases. We also considered the BSSE correction through the counterpoise method and the nuclei-valence electron interactions by including semi-core DFT pseudopotentials.