In-Plane Topological-Defect-Enriched Graphene as an Efficient Metal-Free Catalyst for pH-Universal H2O2 Electrosynthesis.

Developing efficient metal-free catalysts to directly synthesize hydrogen peroxide (H2O2) through a 2-electron (2e) oxygen reduction reaction (ORR) is crucial for substituting the traditional energy-intensive anthraquinone process. Here, in-plane topological defects enriched graphene with pentagon-S and pyrrolic-N coordination (SNC) is synthesized via the process of hydrothermal and nitridation. In SNC, pentagon-S and pyrrolic-N originating from thiourea precursor are covalently grafted onto the basal plane of the graphene framework, building unsymmetrical dumbbell-like S─C─N motifs, which effectively modulates atomic and electronic structures of graphene. The SNC catalyst delivers ultrahigh H2O2 productivity of 8.1, 7.3, and 3.9 mol gcatalyst -1 h-1 in alkaline, neutral, and acidic electrolytes, respectively, together with long-term operational stability in pH-universal electrolytes, outperforming most reported carbon catalysts. Theoretical calculations further unveil that defective S─C─N motifs efficiently optimize the binding strength to OOH* intermediate and substantially diminish the kinetic barrier for reducing O2 to H2O2, thereby promoting the intrinsic activity of 2e-ORR.

[Sc©[3]CPP]+: A Viable Metal-Centered [3]Cycloparaphenylene.

[n]Cycloparaphenylenes ([n]CPPs, n denotes the number of phenyl groups) are difficult to synthesize because of the strain related to their bent phenyl rings. In particular, the strain in [3]CPP is high enough to destroy the π electron delocalization, leading to the spontaneous structural transition to an energetically more stable "bond-shift" (BS) isomer ([3]BS). In this contribution, we propose to achieve [3]CPP by enhancing the π electron delocalization through hosting a guest metal atom. Our computations revealed that Sc could stabilize [3]CPP by forming the [Sc©[3]CPP]+ complex through the favorable π-Sc donation-backdonation interactions. Thermodynamically, the binding energy between the Sc atom and [3]CPP was -205.7 kcal/mol, which could well compensate not only the energy difference of 44.2 kcal/mol between [3]CPP and [3]BS but also the extremely high strain energy of 170.3 kcal/mol in [3]CPP. Simultaneously, the [Sc©[3]CPP]+ complex is stable up to 1500 K in dynamic simulations, suggesting its high viability in the synthesis.

Bifunctional diatomic site catalysts supported by ß12-borophene for efficient oxygen evolution and reduction reactions.

Efficient bifunctional catalysts for oxygen evolution and reduction reactions (OERs/ORRs) are of great importance for sustainable and renewable clean energy, especially for metal-air batteries. Herein, we investigated ß12-borophene with double-hole sites capped with 3d transition metal atoms to explore its catalyst performance for hydrogen evolution reactions (HERs), OERs and ORRs. It was found that the borophene is a good platform for diatomic site catalysts (DASCs) due to their advantage of stability over the corresponding single-atom catalysts (SACs) or clusters. The HER performance of DASCs on ß12-BM was further improved compared to the SAC case. Furthermore, the supported FeNi DASC exhibited good catalytic performance for both OERs and ORRs, the overpotentials for which were 0.43 and 0.55 V, respectively, better than those of the corresponding supported Ni or Fe SAC due to synergistic effects. We herein propose a novel descriptor involving the Bader charges of coordinated atoms explicitly, behaving much better than the d-band center and integrated crystal orbital Hamilton population (-ICOHP) for DASCs. The synergistic effect of Fe-Ni pairs balanced the too strong binding of OH and further activated OH to achieve better catalytic performance. The results of this study can provide theoretical guidance for the design of efficient bifunctional electrocatalysts.

Lanthanide/actinide boride nanoclusters and nanomaterials based on boron frameworks consisting of conjoined Bn rings (n = 7-9).

Extensive global minimum searches augmented with first-principles theory calculations performed in this work indicate that the experimentally observed perfect inverse sandwich lanthanide boride complexes D7h La2B7- (1), D8h La2B8 (3), D9h La2B9- (7) can be extended to their actinide counterparts C2v Ac2B7- (1'), D8h Ac2B8 (3'), D9h Ac2B9- (7') with a Bn monocyclic ring (n = 7-9) sandwiched by two Ac dopants. Such M2Bn-/0 inverse sandwiches (1/1', 3/3', 7/7') can be used as building blocks to generate the ground-state C2 La4B13- (2)/Ac4B13- (2'), D2 La4B15- (4)/Ac4B15- (4'), C3v/C3 La4B18 (5)/Ac4B18 (5'), Oh Ac7B24+ (6'), Oh Ac7B24, Td Ac4B24 (8'), C1 La5B24+ (9)/Ac5B24+ (9'), and Td Ac4B29- (10') which are based on boron frameworks consisting of multiple conjoined Bn rings (n = 7-9). Detailed bonding analyses show that effective (d-p)σ, (d-p)π and (d-p)δ coordination bonds are formed between the Bn rings and metal doping centers, conferring three-dimensional aromaticity and extra stability to the systems. In particular, the perfect body-centered cubic Oh Ac7B24+ (6') and Oh Ac7B24 with six conjoined B8 rings can be extended in x, y, and z dimensions to form one-dimensional Ac10B32 (11'), two-dimensional Ac3B10 (12'), and three-dimensional AcB6 (13') nanomaterials, presenting a B8-based bottom-up approach from metal boride nanoclusters to their low-dimensional nanomaterials.

Compression-induced crimping of boron nanotubes from borophenes: a DFT study.

Several borophenes have been prepared successfully, but the synthesis of boron nanotubes is still very difficult. Our results suggest that the high flexibility of borophene in combination with van der Waals interactions makes it possible to coil boron nanotubes from rippled borophenes, which is confirmed by ab initio molecular dynamics simulations. The plane structures transform into rippled structures almost without any barrier under very small compression and weak perturbations like molecular adsorption. The compression energies of the rippled structures increase linearly and slowly with the increase of the compression. This suggests how the geometry of the borophene evolves with compression. Based on the evaluation of the free energy of hydrogen adsorption, a stronger compression suggests the improved hydrogen evolution performance of the borophene and even makes it better than Pt catalysts. Meanwhile, good hydrogen evolution performance is also suggested for boron nanotubes. Our results suggest a novel preparation method for boron nanotubes from borophenes and a possible way to improve their hydrogen evolution performance.

La@[La5&B30]0/-/2-: endohedral trihedral metallo-borospherenes with spherical aromaticity.

It is well-known that transition-metal-doping induces dramatic changes in the structures and bonding of small boron clusters, as demonstrated by the newly observed perfect inverse sandwich D8h [La(η8-B8)La] and D9h [La(η9-B9)La]-. Based on extensive global minimum searches and first-principles theory calculations, we predict herein the possibility of perfect endohedral trihedral metallo-borospherene D3h La@[La5&B30] (1, 3A'1) and its monoanion Cs La@[La5&B30]- (2, 2A') and dianion D3h La@[La5&B30]2- (3, 1A'1). These La-doped boron clusters are composed of three inverse sandwich La(η8-B8)La on the waist and two inverse sandwich La(η9-B9)La on the top and bottom which share one apex La atom at the center and six periphery B2 units between neighboring η8-B8 and η9-B9 rings, with three octo-coordinate La atoms and two nona-coordinate La atoms as integrated parts of the cage surface. Detailed adaptive natural density partitioning (AdNDP) and iso-chemical shielding surface (ICSS) analyses indicate that La@[La5&B30]0/-/2- (1/2/3) are spherically aromatic in nature. The one-dimensional nanowire La4B21 (4, P31m) constructed from D3h La@[La5&B30] (1) along the C3 axis of the system appears to be metallic. The IR and Raman spectra of La@[La5&B30] (1) and photoelectron spectroscopy of the slightly distorted Cs La@[La5&B30]- (2) are theoretically simulated to facilitate their spectroscopic characterizations.

Fluxional bonds in quasi-planar B 18 2 - and half-sandwich MB 18 - (M = K, Rb, and Cs).

Detailed molecular orbital and bonding analyses reveal the existence of both fluxional σ- and π-bonds in the global minima Cs B 18 2 - (1) and Cs MB18 (3) and transition states Cs B 18 2 - (2) and Cs MB 18 - (4) of B 18 2 - dianion and MB 18 - monoanions (M = K, Rb, and Cs). It is the fluxional bonds that facilitate the fluxional behaviors of the quasi-planar B 18 2 - and half-sandwich MB 18 - which possess energy barriers smaller than the difference of the corresponding zero-point corrections. © 2019 Wiley Periodicals, Inc.

Fluxional Bonds in Planar B19 - , Tubular Ta@B20 - , and Cage-Like B39.

Based on detailed bonding analyses on the fluxional behaviors of planar B19 - , tubular Ta@B20 - , and cage-like B39 - , we propose the concept of fluxional bonds in boron nanoclusters as an extension of the classical localized bonds and delocalized bonds in chemistry. © 2018 Wiley Periodicals, Inc.

Low-dimensional functional networks of cage-like B40 with effective transition-metal intercalations.

As the first all-boron fullerene observed in experiments, cage-like borospherene B40 has attracted considerable attention in recent years. However, B40 has been proved to be chemically reactive and tends to coalesce with one another via the formation of covalent bonds. We explore herein the possibility of low-dimensional functional networks of B40 with effective transition-metal intercalations. We find that the four equivalent B7 heptagons on the waist of each B40 can serve as effective ligands to coordinate various transition metal centers in exohedral motifs. The intercalated metal atoms entail these networks with a variety of intriguing properties. The two-dimensional (2D) Cr2B40 network is a ferromagnetic metal while the 2D Zn2B40 network becomes semiconducting. In contrast, other 2D M2B40 (M = Sc, Ti, V, Mn, Fe, Co, Ni and Cu) networks and 1D CrB40 belong to nonmagnetic metals. The 3D Cr3B40 network is a magnetic metal. This work presents the viable possibility of assembling Mn&B40 metalloborospherenes into stable functional nanomaterials via effective transition-metal intercalations with potential applications in electronic and spintronic devices.

High-symmetry tubular Ta@B183-, Ta2@B18, and Ta2@B27+ as embryos of α-boronanotubes with a transition-metal wire coordinated inside.

Transition-metal doping leads to dramatic structural changes and results in novel bonding patterns in small boron clusters. Based on the experimentally derived mono-ring planar C9v Ta©B92- (1) and extensive first-principles theory calculations, we present herein the possibility of high-symmetry double-ring tubular D9d Ta@B183- (2) and C9v Ta2@B18 (3) and triple-ring tubular D9h Ta2@B27+ (4), which may serve as embryos of single-walled metalloboronanotube α-Ta3@B48(3,0) (5) wrapped up from the recently observed most stable free-standing boron α-sheet on a Ag(111) substrate with a transition-metal wire (-Ta-Ta-) coordinated inside. Detailed bonding analyses indicate that, with an effective dz2-dz2 overlap on the Ta-Ta dimer along the C9 molecular axis, both Ta2@B18 (3) and Ta2@B27+ (4) follow the universal bonding pattern of σ + π double delocalization with each Ta center conforming to the 18-electron rule, providing tubular aromaticity to these Ta-doped boron complexes with magnetically induced ring currents. The IR, Raman, and UV-vis spectra of 3 and 4 are computationally simulated to facilitate their future experimental characterization.

Aromatic cage-like B34 and B35+: new axially chiral members of the borospherene family.

Shortly after the discovery of all-boron fullerenes D2d B40-/0 (borospherenes), the first axially chiral borospherenes C3/C2 B39- were characterized in experiments in 2015. Based on extensive global minimum searches and first-principles theory calculations, we present herein two new axially chiral members to the borospherene family: the aromatic cage-like C2 B34(1) and C2 B35+(2). Both B34(1) and B35+(2) feature one B21 boron triple chain on the waist and two equivalent heptagons and hexagons on the cage surface, with the latter being obtained by the addition of B+ into the former at the tetracoordinate defect site. Detailed bonding analyses show that they follow the universal bonding pattern of σ + π double delocalization, with 11 delocalized π bonds over a σ skeleton. Extensive molecular dynamics simulations show that these borospherenes are kinetically stable below 1000 K and start to fluctuate at 1200 K and 1100 K, respectively. The IR, Raman, and UV-vis spectra of 1 and 2 are computationally simulated to facilitate their experimental characterization.

Charge-induced structural transition between seashell-like B29- and B29+ in 18 π-electron configurations.

Recent joint experimental and theoretical investigations have shown that seashell-like C2 B28 is the smallest neutral borospherene reported to date, while seashell-like Cs B29- (1-) as a minor isomer competes with its quasi-planar counterparts in B29- cluster beams. Extensive global minimum searches and first-principles theory calculations performed in this work indicate that with two valence electrons detached from B29-, the B29+ monocation favors a seashell-like Cs B29+ (1+) much different from Cs B29- (1-) in geometry which is overwhelmingly the global minimum of the system with three B7 heptagonal holes in the front, on the back, and at the bottom, respectively, unveiling an interesting charge-induced structural transition from Cs B29- (1-) to Cs B29+ (1+). Detailed bonding analyses show that with one less σ bond than B29- (1-), Cs B29+ (1+) also possesses nine delocalized π-bonds over its σ-skeleton on the cage surface with a σ + π double delocalization bonding pattern and follows the 2(n + 1)2 electron counting rule for 3D spherical aromaticity (n = 2). B29+ (1+) is therefore the smallest borospherene monocation reported to date which is π-isovalent with the smallest neutral borospherene C2 B28. The IR, Raman, and UV-vis spectra of B29+ (1+) are computationally simulated to facilitate its spectroscopic characterization.

A novel borophene featuring heptagonal holes: a common precursor of borospherenes.

We propose a novel stable borophene (referred to as H-borophene) by tiling seven-membered rings side by side, which is a novel construction pattern never reported in boron sheets or other sheets. It is able to serve as the common precursor of borospherenes (e.g., B39-, B40, B41+, and B422+). Interestingly, a Dirac point appeared at about 0.33 eV below the Fermi level. We found that nanotubes formed by rolling up H-borophene had a great advantage over other boron nanotubes in the case of high curvature, which accounted for the reason why heptagons were preferred in borospherenes. Our study not only proposes a common precursor of borospherenes, but also expands the construction patterns of monolayer sheets.

A first-principles study on zigzag phosphorene nanoribbons passivated by iron-group atoms.

We performed a first-principles study on Fe-, Co-, and Ni-terminated zigzag phosphorene nanoribbons (ZPNRs) with different widths. Magnetic edges were observed for Fe- and Co-terminated ZPNRs, whereas Ni-terminated ZPNRs were nonmagnetic. Interestingly, magnetism could be induced in Ni-ZPNRs by external electric fields, and the distribution of the magnetic moments could be tuned by the direction of the electric fields. Furthermore, Fe-ZPNRs and Co-ZPNRs exhibit semi-metallic and metallic characteristics, respectively, whereas Ni-ZPNRs are mainly semiconductors with band gaps generally increasing monotonously with the increase in nanoribbon width. These fascinating properties of iron-group atom terminated ZPNRs indicate their great potential applications in future spintronics, optoelectronics, and information technologies.

Double-ring tubular (B2O2)n clusters (n = 6-42) rolled up from the most stable BO double-chain ribbon in boron monoxides.

Based on extensive global searches and first-principles theory calculations, we present herein the possibility of double-ring tubular (B2O2)n clusters (n = 6-42) (2-10) rolled up from the most stable one-dimensional (1D) BO double-chain ribbon (1) in boron monoxides. Tubular (3D) (B2O2)n clusters (n ≥ 6) are found to be systematically much more stable than their previously proposed planar (2D) counterparts, with a 2D-3D structural transition at B12O12 (2). Detailed bonding analyses on 3D (B2O2)n clusters (2-10) and their precursor 1D BO double-chain ribbon (1) reveal two delocalized B-O-B 3c-2e π bonds over each edge-sharing B4O2 hexagonal unit which form a unique 6c-4e o-bond to help stabilize the systems. The IR, Raman, UV-vis, and photoelectron spectra of the concerned species are computationally simulated to facilitate their experimental characterization.

Cage-like B39+ clusters with the bonding pattern of σ + π double delocalization: new members of the borospherene family.

The recently observed cage-like borospherenes D2d B40-/0 and C3/C2 B39- have attracted considerable attention in chemistry and materials science. Based on extensive global minimum searches and first-principles theory calculations, we present herein the possibility of cage-like Cs B39+ (1) and Cs B39+ (2) which possess five hexagonal and heptagonal faces and one filled hexagon and follow the bonding pattern of σ + π double delocalization with 12 delocalized π bonds over a σ-skeleton, adding two new members to the borospherene family. IR, Raman, and UV-vis spectra of Cs B39+ (1) and Cs B39+ (2) are computationally simulated to facilitate their experimental characterization.

Structural transition in metal-centered boron clusters: from tubular molecular rotors Ta@B21 and Ta@B22+ to cage-like endohedral metalloborospherene Ta@B22.

Inspired by the recent discovery of the metal-centered tubular molecular rotor Cs B2-Ta@B18- with the record coordination number of CN = 20 and based on extensive first-principles theory calculations, we present herein the possibility of the largest tubular molecular rotors Cs B3-Ta@B18 (1) and C3v B4-Ta@B18+ (2) and smallest axially chiral endohedral metalloborospherenes D2 Ta@B22- (3 and 3'), unveiling a tubular-to-cage-like structural transition in metal-centered boron clusters at Ta@B22-via effective spherical coordination interactions. The highly stable Ta@B22- (3) as an elegant superatom, which features two equivalent corner-sharing B10 boron double chains interconnected by two B2 units with four equivalent B7 heptagons evenly distributed on the cage surface, conforms to the 18-electron configuration with a bonding pattern of σ + π double delocalization and follows the 2(n + 1)2 electron counting rule for spherical aromaticity (n = 2). Its calculated adiabatic detachment energy of ADE = 3.88 eV represents the electron affinity of the cage-like neutral D2 Ta@B22 which can be viewed as a superhalogen. The infrared, Raman, VCD, and UV-vis spectra of the concerned species are computationally simulated to facilitate their spectral characterizations.

Saturn-like charge-transfer complexes Li4&B36, Li5&B36⁺, and Li6&B36²âº: exohedral metalloborospherenes with a perfect cage-like B364⁻ core.

Based on extensive first-principles theory calculations, we present the possibility of construction of the Saturn-like charge-transfer complexes Li4&B36 (2), Li5&B36(+) (3), and Li6&B36(2+) (4) all of which contain a perfect cage-like B36(4-) (1) core composed of twelve interwoven boron double chains with a σ + π double delocalization bonding pattern, extending the Bn(q) borospherene family from n = 38-42 to n = 36 with the highest symmetry of T(h).

Endohedral Ca@B38: stabilization of a B38(2-) borospherene dianion by metal encapsulation.

Based on extensive global-minimum searches and first-principles electronic structure calculations, we present the viability of an endohedral metalloborospherene Cs Ca@B38 () which contains a Cs B38(2-) () dianion composed of interwoven boron double chains with a σ + π double delocalization bonding pattern, extending the Bn(q) (q = n - 40) borospherene family from n = 39-42 to n = 38. Transition metal endohedral complexes Cs M@B38 (M = Sc, Y, Ti) (, , ) based on Cs B38(2-) () are also predicted.

Endohedral C3 Ca@B39(+) and C2 Ca@B39(+): axially chiral metalloborospherenes based on B39(-).

Using the newly discovered borospherenes C3 B39(-) and C2 B39(-) as molecular devices and based on extensive global-minimum searches and first-principles calculations, we present herein the possibility of the first axially chiral metalloborospherenes C3 Ca@B39(+) (, (1)A) and C2 Ca@B39(+) (, (1)A), which are the global minimum and the second lowest-lying isomer of CaB39(+), respectively. These metalloborospherene species turn out to be charge-transfer complexes Ca(2+)@B39(-) in nature, with the Ca centre on the C3 or C2 molecular axis donating one electron to the B39 cage which behaves like a superhalogen. Molecular orbital analyses indicate that C3/C2 Ca(2+)@B39(-) possess the universal bonding pattern of σ plus π double delocalization, similar to their C3/C2 B39(-) parents. Molecular dynamics simulations show that both C3 Ca@B39(+) () and C2 Ca@B39(+) () are dynamically stable at 200 K, with the former starting to fluctuate structurally at 300 K and the latter at 400 K, again similar to C3/C2 B39(-). The infrared and Raman spectra of C3/C2 Ca@B39(+) (/) are simulated and compared with those of C3/C2 B39(-) to facilitate their forthcoming experimental characterization.