A wide-bandgap graphene-like structure C6BN with ultra-low dielectric constant.

This study introduces a new wide-bandgap graphene-like structure, denoted as C6BN, achieved by incorporating an eight-electron BN pair, substantially modifying its electronic properties. Utilizing extensive density functional calculations, we comprehensively analyzed the stability, electronic structure, mechanical properties, and optical-electrical characteristics of C6BN. Our investigations reveal the material's exceptional thermodynamic, mechanical, and dynamic stability. Notably, the calculated wide bandgap of 2.81 eV in C6BN, supported by analyses of energy levels, band structures, and density of states, positions it as a promising two-dimensional wide-bandgap semiconductor. Additionally, C6BN exhibits isotropic mechanical features, highlighting its inherent flexibility. Remarkably, our calculations indicate an ultra-low dielectric constant (k = 1.67) for C6BN, surpassing that of well-established third-generation semiconductors. Further exploration into the thermoelectric properties of C6BN demonstrates its promising performance, as evidenced by calculations of thermal conductivity (κ), power factor (P), and Seebeck coefficient (S). In summary, our findings underscore the significant potential of the proposed C6BN structure as a flexible two-dimensional material poised to drive future advancements in electronic and energy-related technologies.

Insight into the interaction of host-guest structures for pyrrole-based metal compounds and C70.

This study focuses on the recognition and isolation of fullerenes, which are crucial for further exploration of their physical and chemical properties. Our goal is to investigate the potential recognition of the D5h-C70 fullerene using crown-shaped metal compositions through density functional theory calculations. We assess the effectiveness of fullerene C70 recognition by studying the binding energy. Additionally, various analyses were conducted, including natural bond order charge analysis and reduced density gradient analysis, to understand the interaction mechanism between the host and guest molecules. These investigations provide valuable insights into the nature of the interaction and the stability of the host-guest system. To facilitate the release of the fullerene guest molecule, the vis-NIR spectra were simulated for the host-guest structures. This analysis offers guidance on the specific wavelengths that can be utilized to release the fullerene guest from the host-guest structures. Overall, this work proposes a new strategy for the effective recognition of various fullerene molecules and their subsequent release from host-guest systems. These findings could potentially be applied in assemblies involving fullerenes, advancing their practical applications.

Synergistic regulation of chloride anion recognition using a triple-functional sites receptor with two different cationic effectors.

The synergistic regulation of the multi-functional sites on one receptor molecule with different cationic effectors for anion recognition is scarce to be well understood from the experiment and theory. In this work, a new anion receptor with three functional zones including ether hole, biurea and double bipyridine groups (EUPR) is designed expecting to enhance the chloride anion recognition together with a rational synthesis path being proposed based on four simple and mature organic reaction steps. The conformational structures of the designed receptor EUPR and the binding behaviors for three kinds of ions (Cl-, Na+, and Ag+) are deeply investigated by using density functional theoretical calculations. It is found that Cl- binding via the hydrogen bond interaction can be significantly enhanced and synergistically regulated by the two kinds of cations and the corresponding conformational changes of receptor EUPR. Especially, the conformational pre-organization of receptor caused by the encapsulation of sodium ion into ether hole is benefit to the binding for Cl- in both thermodynamics and kinetics. Na+ binding, in turn, can ever be enhanced by chloride anion, whereas it seems that Ag+ binding cannot always be enhanced by chloride anion, reflecting an electrical complementary matching and mutual enhancement effect for different counter ions. Moreover, solvent effect calculations indicate that EUPR may be an ideal candidate structure for Cl- recognition by strategy of counter ion enhancement in water. Additionally, a visual study of intermolecular noncovalent interaction (NCI) and molecular electrostatic potential (ESP) are used for the analysis on the nature of interactions between receptor and bound ions.

Regenerable and Highly Stable Two-Dimensional Imine-Based Covalent Organic Framework for Simultaneous Rapid Detection and Adsorption of Cu2+ Ions.

The development of efficient fluorescent probes and adsorbents for detecting and removing Cu2+, which pose potential environmental and health risks, is a highly active area of research. However, achieving simultaneously improved fluorescence detection efficiency and enhanced adsorption capacity in a single porous probe remains a significant challenge. In this study, we successfully synthesized a two-dimensional imine-based TAP-COF using 2,4,6-triformylphloroglucinol and tri(4-aminophenyl)amine as raw materials. TAP-COF exhibited excellent properties, including a large specific surface area of 685.65 m2·g-1, exceptional thermal stability (>440 °C), chemical stability, temporal stability, and recyclability. Fluorescence testing revealed that TAP-COF exhibited remarkable specificity and high sensitivity for detecting Cu2+. The fluorescence mechanism, in which the excited state intramolecular proton transfer was impeded by the interaction of Cu2+ with C═O and C-N bonds on TAP-COF upon the addition of Cu2+, was further elucidated through experimental and theoretical methods. Furthermore, the adsorption capacity of TAP-COF toward Cu2+ was investigated, confirming the excellence of TAP-COF as a fluorescent probe and adsorbent for the specific detection and removal of Cu2+. This work holds significant implications for improving environmental and human health concerns associated with Cu2+ contamination.

Nanoscale Saturn Systems Based on C60/70 Bucky Ball and a Newly Designed [4]Cyclopara-1,2-diphenylethylene Hoop: A Strategy for Fullerene Encapsulation Release and Selective Recognition for C70.

A new carbonaceous nanohoop, [4]cyclopara-1,2-diphenylethylene ([4]CPDPE, composed by four 1,2-diphenylethylene units linked via the para of the phenyls), is designed together with two rational synthesis paths being proposed. The Saturn-like host-guest systems formed with the [4]CPDPE nanoring and fullerene C60/70 are explored using density functional theory calculations. The results evidence that the geometry mutual matching between [4]CPDPE and C60/70 is perfect, and the [4]CPDPE⊃C60/70 complexes could be formed spontaneously with high binding energies. Thermodynamic calculation results show that it essentially prefers to selectively recognize C70 over its smaller cousin C60. More interestingly, the [4]CPDPE nanoring could present the regular ring cylinder and the saddle shapes via configuration transformation between its all-trans form and all-cis form, so as to theoretically realize the fullerene encapsulation and release under photoirradiation. Furthermore, the 2:1 interaction structure ([4]CPDPE2⊃Dimer-C60) and properties are investigated. Additionally, the ultraviolet-visible (UV-vis) spectra are simulated, and host-guest noncovalent interaction (NCI) regions are investigated based on the electron density and reduced density gradient (RDG), which may be helpful for a deep understanding of the present designed systems in future.

Metal Atoms (Li, Na, and K) Tuning the Configuration of Pyrrole for the Selective Recognition of C60.

Host-guest structure assembly is significant in the recognition of molecules, and the fullerene-based host-guest structure is a convenient method to determine the structures of fullerenes of which recognition is with many difficulties in experiments. Here, with density functional theory calculations, we designed several crown-shaped pyrrole-based hosts tuned by doping metal atoms (Li, Na, and K) for the effective recognition of C60 with modest interaction between the host and guest. Binding energy calculations showed an enhanced interaction of the concave-convex host-guest system with the doped metal atoms, enabling the selective recognition of C60. The electrostatic interaction between the host and guest was studied by the natural bond order charge analysis, reduced density gradient, and electrostatic potential. Furthermore, the UV-vis-NIR spectra of host-guest structures were simulated to give guidance on the release of the fullerene guest. With much expectation, this work would give a new strategy to design new hosts for effectively recognizing much more fullerene molecules with modest interaction and would be useful for the assembly involving fullerenes.

Grape bunches of novel conjugated chain bonded fullerene oligomers: design of a potential electron trap carbonaceous molecular material.

Developing π electron conjugated groups as covalent bonded bridges between fullerenes in their oligomers is key to optimizing and maximizing functions of the fullerene-based materials. In this work, a series of novel conjugated chain bonded fullerene C60 oligomers (CBFOs) with a well-defined nano-architecture and "grape bunches" shapes are rationally designed and viably constructed based on fullerene-carbenes by means of DFT calculations. The results show that the presently designed CBFOs present a much better electron-accepting ability together with a much lower reorganization energy than the isolated fullerene C60, and characterized as the potential ideal candidate for electron acceptors. The frontier molecular orbital and electron density analysis can well support the results of diabatic electron affinity (EAa) and vertical electron affinity (EAv) calculations. Moreover, these CBFOs exhibit strong absorption in the visible region but no obvious absorption in the ultraviolet region. In addition, the optical properties of the CBFOs and two dimensional structure are also simulated and explored theoretically. We hope that the present study would be helpful for developing covalent-bonded-fullerene based electron trap molecular materials, building blocks of nano-devices and nano-machinery applications.

Composition-selective full inclusion host-guest interaction of azobenzene-containing photoresponsive nanoring with fullerene C60.

By means of density functional theory calculations, the encapsulation capabilities of a series of azobenzen-containing photoresponsive nanoring hosts (labeled as host 1, 2, 3, 4, 5 and 6 according to the number of the azo unit, respectively) for fullerene C60 were surveyed. Interestingly and abnormally, it is found that the host 5, of which the diameter is only 1.218 nm, can form stable full inclusion complex with C60 . However, irrespective of their cavity sizes (11.98 ~ 12.94 Å) of the hosts, the structures 1 ~ 4 and 6 were all disable to form inclusion complex with C60 . In this paper, the group-number-composition-selective full inclusion host-guest interaction of the azobenzene-containing nanorings with fullerene C60 is firstly presented. The calculated interaction energies, together with the detection and visualization of the weak interaction regions, provided evidences for the host-guest binding based on relative strong repulsion interaction in the full inclusion complex. Analysis on the frontier orbital feature of the host-guest systems suggests that under the electron excited condition, the chemical activity may be transferred from host 5 to guest C60 by formation of the floating host-guest complex, and the chemical reactivity of the host 5 can be passivated via formation of the full inclusion host-guest complex. Additionally, UV-vis-NIR and 1 H NMR spectra of the hosts before and after the formations of the complexes have been simulated and discussed qualitatively, which may be helpful for further experimental investigations in future.

Theoretically modelling graphene-like carbon matryoshka with strong stability and particular three-center two-electron π bonds.

Carbon materials based on different hybridization of carbon atoms have drawn great attention because of their unique configurations and physical and chemical properties. Here, a previously unknown 2D carbon allotrope named L-2Gy, graphene-like carbon matryoshka graphynes (Gy) with two alkynyls (C[triple bond, length as m-dash]C) inserted into the three-fold carbon atoms of graphene, has been constructed with considerable thermal, dynamical, and mechanical stability by using ab initio density functional theory. With the increasing number of alkynyls between the three-fold carbon atoms of graphene, the stability of Gy will seriously decrease. L-2Gy has a fascinating chemical bond environment consisting of sp- and sp2-hybridized carbon atoms, and delocalized π electrons derived from the 27 three-center two-electron π bonds. This particular electronic structure plays a vital role in chemically stabilizing L-2Gy. The electronic band structure reveals the semi-metallic features of L-2Gy mainly contributed by the px/z orbitals of carbon atoms. Furthermore, compared with the acknowledged catalysts for the hydrogen evolution reaction (HER), L-2Gy, as a 2D carbon allotrope, shows excellent catalytic activity for the HER.

Significant Roles of a Particularly Stable Two-Center Two-Electron Lu-Lu σ Bond in Lu2@C86: Electronic Structure of Lu and Radius of Lu2.

There is still dispute over the stability of endohedral metallofullerenes (EMFs) M2C2n, and recently, multiform lutetium-based dimetallofullerenes have been dropped in experiments. The thermodynamic stabilities of Lu2C86 EMFs are revealed by density functional theory (DFT) in conjunction with statistical thermodynamic analyses. Inevitably, besides the experimentally reported Lu2@C2v(63751)-C86, Lu2@Cs(63750)-C86, and Lu2@Cs(63757)-C86, other three metal carbide clusterfullerenes, Lu2C2@D2d(51591)-C84, Lu2C2@C1(51383)-C84, and Lu2C2@Cs(id207430)-C84, rather than Lu2@C86 are first characterized as thermodynamically stable isomers of Lu2C86. Specially, the Cs(id207430)-C84 is a newly non-classical fullerene containing one heptagon, which is stabilized via encaging Lu2C2. Another interesting phenomenon is that the outer fullerene cages of thermodynamically stable Lu2C82-88 molecules are geometrically connected through C2 addition/loss and Stone-Wales (SW) transformation, suggesting a special relationship between thermodynamic stabilities and geometries of Lu2C82-88 EMFs. Furthermore, the electronic configurations of (Lu2)4+@C864- and (Lu2C2)4+@C844- were confirmed. A significantly stable two-center two-electron (2c-2e) Lu-Lu σ single bond is formed in Lu2@C86. By comparing M-M bonds in M2@C2v(63751)-C86 (M = Sc, Y, La, and Lu), two significant factors, the valence atomic orbital (ns) of metal atoms and radius of M2+, are found to determine the stability of the M-M bond in the C2v(63751)-C86. Additionally, the simulated UV-vis-NIR spectra of thermodynamically stable Lu2C86 isomers were simulated, which further disclose their electronic features.

Theoretical Insight into Thermodynamically Optimal U@C84: Three-Electron Transfer Rather Than Four-Electron Transfer.

Four-electron transfer from U to the fullerene cage commonly exists in U@C2n (2n < 82) so far, while four- and three-electron transfers, which depend on the cage isomers, simultaneously occur in U@C82. Herein, detailed quantum-chemical methods combined with statistical thermodynamic analysis were applied to deeply probe into U@C84, which is detected in the mass spectra without any further exploration. With triplet ground states, novel isomers including isolated-pentagon-rule U@C2(51579)-C84 and U@D2(51573)-C84 as well as nonisolated-pentagon-rule U@Cs(51365)-C84 were identified as thermodynamically optimal. Surprisingly, there were unexpected three-electron transfers, which directly led to one unpaired electron on the cage, in all of the three isomers. Significant covalent interactions between the cage and U successively weakened for U@D2(51573)-C84, U@C2(51579)-C84, and U@Cs(51365)-C84. Besides, the IR absorption spectra were simulated as a reference for further structural identification in the experiment. Last but not least, the potential reaction sites were predicted to facilitate further functionalization and thus achieve promising applications for U@C84.

Theoretical Investigations of Lu2C84: Unexpected Impact of Metal Electronic Configuration toward the Metal-Metal σ-Bond in Fullerene.

Recent experimental works recovered multiformity of lutetium-involved dimetallofullerenes. On the basis of density functional theory (DFT) combined with statistical thermodynamic analyses, the relative stabilities of Lu2C84 dimetallofullerene were clarified. Besides the experimentally acknowledged Lu2@D2d(51591)-C84 and Lu2@C2v(51575)-C84, another four isomers metallofullerenes, Lu2@C1(51580)-C84, Lu2C2@Cs(39715)-C82, Lu2C2@C3v(39717)-C82, and Lu2C2@C2v(39718)-C82, are first proposed as thermodynamically stable structures. Interestingly, the geometric relationships among the pristine cages of stable Lu2C84 isomers through Stone-Wales transformation or C2 lose/insertion reveal important clues of the fullerene formation mechanism. The ionic interaction in the stable Lu2C84 isomers is revealed, and their valence states are Lu24+@C844- or (Lu2C2)4+@C824-. In the Lu2@C84 isomers, the results of frontier molecular orbital and natural bond orbital analyses suggest that a Lu-Lu single bond is formed, which is mainly composed of the 6s and 6p orbitals of the Lu atoms. Further analyses of the M2@C84 (M = Sc, Y, La, and Yb) structures disclose the importance of the electron configuration of metal element toward the formation of a single metal-metal bond in C84. Moreover, the covalent interaction between the Lu2 moiety and the C84 cages is disclosed, which is a supplement to the ionic model.

A Novel Hyperbolic Two-Dimensional Carbon Material with an In-Plane Negative Poisson's Ratio Behavior and Low-Gap Semiconductor Characteristics.

Poisson's ratio is one of the fundamental features of materials, reflecting the transverse strain response to the applied certain axial strain. The materials with a negative Poisson's ratio, also known as auxetic materials, are rare in nature and attract lots of research interest because of their unusual mechanical behavior and extensive applications in mechanical nanodevices. Here, we proposed and studied a novel hyperbolic two-dimensional graphene-like structure (GLS) showing a negative Poisson's ratio behavior by first-principles calculation. The thermodynamic, dynamic, lattice dynamic, and mechanical stabilities of the GLS were carefully studied. In addition, we also explored the electronic structure, mechanical characteristics, and optical-electronic characteristics. The GLS not only displays a negative Poisson's ratio in certain directions but also shows low-gap semiconductor characteristics and superior electronic conductivity. It is a potential sunscreen material because of the outstanding reflection and absorption for ultraviolet and infrared light.

Potential molecular semiconductor devices: cyclo-Cn (n = 10 and 14) with higher stabilities and aromaticities than acknowledged cyclo-C18.

The successful synthesis and isolation of cyclo-C18 in experiments is a ground-breaking development in carbon rings. Herein, we studied the thermodynamic stabilities of cyclo-Cn (4 ≤ n ≤ 34) with hybrid density functional theory. When n = 4N + 2 (N is an integer), cyclo-Cn were thermodynamically stable. In particular, cyclo-C10 and cyclo-C14 were more thermodynamically, kinetically, dynamically, and optically stable compared with the acknowledged cyclo-C18, and were potential candidates for zero-dimensional carbon rings. Cyclo-Cn (n = 10 and 14) show similar molecular semiconductor characteristics to the acknowledged cyclo-C18. The carbon atoms were sp hybridized in cyclo-C10, cyclo-C14, and cyclo-C18. Cyclo-C14 and cyclo-C18 had alternating abnormal single and triple bonds, but cyclo-C10 had equal bonds. Cyclo-C10, cyclo-C14, and cyclo-C18 with large aromaticities had out-of-plane and in-plane π systems, which were perpendicular to each other. The number of π electrons in the out-of-plane and in-plane π systems, respectively, followed the standard Hückel aromaticity rule. Simulated UV-vis-NIR spectra indicated similar electronic structures of cyclo-C14 and cyclo-C18.

New Insight into U@C80: Missing U@D3(31921)-C80 and Nuanced Enantiomers of U@C1(28324)-C80.

Triplet U@C1(28324)-C80, violating the isolated pentagon rule, is experimentally recognized as the stable isomer for uranium-based endohedral monometallofullerene U@C80. Here we first verified that triplet U@D3(31921)-C80, following the isolated pentagon rule, was to be another thermodynamically stable isomer via density functional theory in conjunction with statistical thermodynamic analysis. U@D3(31921)-C80 was probably missing in the previous experiment and would be a promising isomer in the to-be experiment because of its excellently thermodynamic stability. In addition, the anomalous metal position was revealed in U@D3(31921)-C80 and U@C1(28324)-C80. Four-electron transfer from U to C80 was also revealed for the two isomers. Thus, two unpaired 5f electrons were still in the U for U@D3(31921)-C80 and U@C1(28324)-C80. Moreover, the covalent interactions between U and C80 in U@D3(31921)-C80 were stronger than those in U@C1(28324)-C80. The electrostatic interactions preponderated in the interaction energy ΔEint between U and C80 for U@C1(28324)-C80, and the orbital interactions dominated in the ΔEint for U@D3(31921)-C80. The electrophilic and nucleophilic reactivities were also analyzed for U@D3(31921)-C80 and U@C1(28324)-C80. Electronic circular dichroism spectra were simulated to distinguish the two enantiomers of U@C1(28324)-C80. We are hopeful that this investigation will be valuable for further identification of the two enantiomers in future experiments.

In-Depth Theoretical Probe into Novel Mixed-Metal Uranium-Based Endohedral Clusterfullerenes Sc2UX@Ih(31924)-C80 (X = C, N).

Mixed-metal uranium-based endohedral clusterfullerenes, Sc2UX@C80 (X = C, N), which were recently reported in experiments, have been investigated considering heptagon-containing isomers by density functional theory calculations in conjunction with statistical thermodynamic analysis. The triplet Sc2UC@Ih(31924)-C80 and quartet Sc2UN@Ih(31924)-C80, named after the spiral number (31924), are found to be thermodynamically stable and satisfy aromaticity rules. Furthermore, the restricted movements of the Sc2UX (X = C, N) cluster in Ih(31924)-C80 have been demonstrated via ab initio molecular dynamics simulations. The six-electron transfer from the inner cluster to the cage results in the electronic structures (Sc2UX)6+@C806- (X = C, N), which were also confirmed by natural bond orbital analysis. On the basis of the frontier molecular orbitals, the oxidation states of uranium in Sc2UC@C80 and Sc2UN@C80 are +IV and +III, respectively, with residual electrons in 5f orbitals of U. The chemical bond between U and C (N) of the inner cluster is characterized as a double bond (single bond) by an analysis of the Mayer bond orders. There are covalent interactions between the inner cluster and outer cage, which is clarified by the quantum theory of atoms in molecules. IR spectra of the optimal isomers have also been simulated, which show the clear difference between Sc2UX@C80 (X = C, N). These findings, together with simulated results, are expected to supply useful information in future experiments of mixed-metal uranium-based endohedral clusterfullerenes.

Pivotal Role of Nonmetal Atoms in the Stabilities, Geometries, Electronic Structures, and Isoelectronic Chemistry of Sc3 X@C80 (X = C, N, and O).

The thermodynamic and dynamic stabilities of Sc3 X@C80 (X = C, N, and O) are explored via density functional theory combined with statistical thermodynamic analysis and ab initio molecular dynamics. It is the first time to comprehensively consider the effect of nonmetal atoms on trimetallic endohedral clusterfullerenes. Relative to Sc3 X@Ih (31924)-C80 (X = N and O) with general six-electron transfer, an intriguing electronic structure of unexplored Sc3 C@D5h (31923)-C80 with thermodynamic and dynamic stabilities is clearly disclosed. Natural bond orbitals and charge decomposition analysis simultaneously suggest that one unpaired electron appears on the cage for neutral Sc3 C@D5h (31923)-C80 , which could be prospectively stabilized by effective exohedral derivatization and ionization in the future. Moreover, isoelectronic endohedral clusterfullerenes, (Sc3 C@C80 )- , Sc3 N@C80 , and (Sc3 O@C80 )+ , are also uniquely taken into account. The geometries, electronic structures, reactivities, and reactive sites of isoelectronic species are examined, and it turns out that all the three isoelectronic species would rather electrophilic than nucleophilic reactions. © 2019 Wiley Periodicals, Inc.