B12 Cluster Research Articles

CB11S3+: A Triangular Boron-Based Cluster with One Planar Tetracoordinate Carbon at Its Edge.

Boron-based clusters containing planar tetracoordinate carbon (ptC) are unique and scarce. Isoelectronic-replacing after proper vulcanization is an effective strategy to obtain the ptC based on the B12 cluster. Herein we report computational evidence for a ternary CB11S3+ (C2v, 1A1) cluster, which possesses a concentric double-triangle structure containing one ptC atom at the peripheral edge. The unbiased structural explorations of potential energy surfaces and high-level CCSD(T) calculations indicate that the ptC CB11S3+ cluster is a true global minimum. Born-Oppenheimer molecular dynamics (BOMD) simulations reveal that it is dynamically stable against isomerization and decomposition. Chemical bonding analysis reveals that three delocalized π bonds endow the π aromaticity to the CB11 unit of CB11S3+. In addition, the strong S → B π back-bonding is also conducive to the stability of CB11S3+. The current findings offer opportunities for further boron-based ptC clusters.

Two-Dimensional Transition Metal Boron Cluster Compounds (MBnenes) with Strain-Independent Room-Temperature Magnetism.

Two-dimensional (2D) metal borides (MBenes) with unique electronic structures and physicochemical properties hold great promise for various applications. Given the abundance of boron clusters, we proposed employing them as structural motifs to design 2D transition metal boron cluster compounds (MBnenes), an extension of MBenes. Herein, we have designed three stable MBnenes (M4(B12)2, M = Mn, Fe, Co) based on B12 clusters and investigated their electronic and magnetic properties using first-principles calculations. Mn4(B12)2 and Co4(B12)2 are semiconductors, while Fe4(B12)2 exhibits metallic behavior. The unique structure in MBnenes allows the coexistence of direct exchange interactions between adjacent metal atoms and indirect exchange interactions mediated by the clusters, endowing them with a Néel temperature (TN) up to 772 K. Moreover, both Mn4(B12)2 and Fe4(B12)2 showcase strain-independent room-temperature magnetism, making them potential candidates for spintronics applications. The MBnenes family provides a fresh avenue for the design of 2D materials featuring unique structures and excellent physicochemical properties.

Does photoinduced structural change by β-rhombohedral boron occur at room temperature?

β-rhombohedral boron (β-B) is an intriguing solid among the elements. The crystal structure of β-B is widely accepted as a complex structure based on the B12 clusters, and with a lot of intrinsic structural defects. In the last decade, β-B was proved to be the only elemental semiconductor that exhibits the self-compensation property accompanied by changing structural defects during atom doping. Moreover, it is reported that various physical properties of β-B change discontinuously around 550 K, which may originate from defect diffusion [S. Hoffmann and H. Werheit, Solid State Sciences 14, 1572 (2012)]. We previously reported that a volume expansion of about 1.5% takes place above this temperature (between 650 K and 850 K). On the other hand, this expanded structure is stable in dark conditions for more than 4.5 months. Light irradiation at room temperature reverses the volume back to the initial state, and a possible scenario will be discussed in this paper.

Reinforced photoinduced behavior of a low-cost mechanochemical synthesized Fe-doped B12As2 nanocrystals

Icosahedral boron arsenide B12As2 is a self-healing semiconductor potentially applied in harshly irradiated environments. However, doping effects were rarely investigated to expand their applications. Hereby, a low-cost mechanochemical strategy is proposed to synthesize B12As2 nanocrystals with a boron transformation rate of ∼70%. Nano-B12As2 of 40–50 nm could be self-doped with Fe element and purified by aqua regia. Fe accounts from ∼0.00–1.77 at% with rotational speeds. Based on nano-size effects and Fe-doping effects, the photoluminescence process shows an indirect band-gap at Eg= 2.81 eV and the presence of impurity energy level at E′= 2.11 eV. The optical absorption is red-shifted from the reported UV region to the visible region. The multiply increased photocatalytic hydrogen production (249 μmol∙h−1∙g−1 vs. 92.2 μmol∙h−1∙g−1) and photocurrent density (∼6 times) indicate that Fe-doping enhances the photo-excitement and the separation of the photoinduced carrier. First-principles calculations reveal a robust B12As2 structure doped by Fe, bonding to icosahedral B12 clusters and its nearest As via the Fe(III) style. Doped-Fe alters HOMO and LUMO orbital components, reduces the optical band-gap and becomes the activated carrier-separation center. Overall, a novel synthetic method and mechanism of Fe-doping are revealed that would facilitate optical applications of B12As2 crystals under extreme conditions.

Revealing electrocatalytic C[sbnd]N coupling for urea synthesis with metal–free electrocatalyst

Urea is ubiquitous in agriculture and industry, but its production consumes a lot of energy. The conversion of nitrogen (N2) and carbon dioxide (CO2) into urea via an electrocatalytic CN coupling reaction under ambient conditions would be a major boon to sustainable development. However, designing a metal − free catalyst with high activity and selectivity for urea remains a major challenge. Herein, by means of density functional theory (DFT) and ab − initio molecular dynamics (AIMD) computations, the B12 cluster doped on nitrogenated graphene (C2N) substrate catalyst (B12@C2N) with superior stability was designed for electrocatalytic urea synthesis starting from the CO2 and N2 through four reaction mechanisms. The nature of the co-adsorption activation of CO2 and N2 on the B12@C2N catalyst was investigated, the electrochemical proton − electron transfer steps and the CN thermochemical coupling led to the synthesis of urea. The study showed that the B12@C2N catalyst exhibited high catalytic activity for urea synthesis with the lowest limiting potential of − 1.01 V following the *HNNH mechanism compared with other mechanisms. The potential − determining step (PDS) is the formation of the *CO+*NH2NH2 species. However, the two − step CN coupling barriers of *NCON species are 0.13 eV and 0.60 eV using AIMD and a “slow − growth” sampling approach in an explicit water molecules model. Calculations also showed that the byproducts of carbon monoxide (CO), methane (CH4), methanol (CH3OH), ammonia (NH3), and hydrogen (H2) can be inhibited on the B12@C2N catalyst. Therefore, the metal − free catalyst not only has a good performance for the hydrogenation of CO2 and N2 promoting the electrochemical reaction, but also facilitates CN thermochemical coupling for urea synthesis. This work provides new insights into the synthesis of urea via the CN coupling reaction on a metal − free electrocatalyst, a process that could contribute to greenhouse gas mitigation to help meet carbon neutrality targets.

Structures and chemical bonding of boron-based B12O and B11Au clusters. A counterexample in boronyl chemistry.

Boron oxide clusters have structural diversity and unique chemical bonding, and recent literature has shown that boronyl complexes dominate boron-rich oxide clusters. A counterexample in boronyl chemistry is presented in this work. Using global structural searches, electronic structure calculations, and chemical bonding analyses, we shall report on the computational design of two boron-based quasi-planar or planar clusters: B12O and B11Au. Contrary to expectation, the B12O cluster has a circular quasi-planar shape with a peripheral B-O-B bridge, which resembles bare B12 cluster. It does not contain a boronyl ligand. The isomeric boronyl complex turns out to be 10.32 kcal mol-1 higher in energy at the single-point CCSD(T) level. In contrast, B11Au cluster behaves normally with an elongated B11 moiety and a terminal Au ligand. Chemical bonding analyses reveal three-fold π/σ aromaticity in circular B12O cluster, including global 6π aromaticity, as well as spatially isolated inner 2σ aromaticity and outer 10σ aromaticity. The three-fold 6π/2σ/10σ aromaticity underlies the stability of B12O cluster. This bonding picture is unknown for bare B12 cluster and its derivatives. The elongated B11Au cluster has conflicting π/σ aromaticity (with 6π versus 8σ electron-counting). The B12O cluster is actually isoelectronic with bare B12 cluster in terms of delocalized π/σ bonding, which inherits the structural and electronic robustness of the latter.

A New Composite Material on the Base of Carbon Nanotubes and Boron Clusters B12 as the Base for High-Performance Supercapacitor Electrodes

We explore the quantum capacitance, stability, and electronic properties of single-walled carbon nanotubes decorated with B12 icosahedral boron clusters by first-principle calculation methods implemented in the SIESTA code. After the optimization of the built supercells, the B12 clusters formed bonds with the walls of the carbon nanotubes and demonstrated metallic properties in all cases. The network of carbon nanotubes with its large area and branched surface is able to increase the capacity of the electric double-layer capacity, but the low quantum capacity of each nanotube in this network limits its application in supercapacitors. We found that the addition of boron clusters to both the outer and inner walls increased the quantum capacitance of carbon nanotubes. The calculation of the transmission function near the Fermi energy showed an increase in the conductivity of supercells. It was also found that an increase in the concentration of boron clusters in the structure led to a decrease in the heat of formation that positively affects the stability of supercells. The calculation of the specific charge density showed that with an increase in the boron concentration, the considered material demonstrated the properties of an asymmetric electrode.

A Series of Pentanary Salt-Inclusion Chalcogenoborates Containing a B12Q12 (Q = S, Se) Cluster Exhibiting a Kleinman-Forbidden Frequency-Doubling Effect.

A series of pentanary chalcogenoborates (A3X)[InB12(InQ4)3] (A = K, Rb, Cs; X = Cl, Br, I; Q = S, Se) were obtained by high-temperature solid-state reactions. These salt-inclusion chalcogenides crystallize in the hexagonal space group P6322, a type of Kleinman-forbidden noncentrosymmetric structure. Their structures feature a [InB12(InQ4)3] open framework built by InQ6 octahedra and InQ4 tetrahedra consolidated B12 cluster, which accomodates octahedral cavities for XA6 units. They are second-harmonic generation active, and their optical properties were studied experimentally and theoretically. This work can evoke more interest in chalcogenoborate-based second-order nonlinear optical materials.

Structures, Electronic, and Spectral Properties of Doped Boron Clusters MB12 0/- (M = Li, Na, and K).

Structures and electronic properties of alkali metal atom-doped boron clusters MB120/– (M = Li, Na, K) are determined using the CALYPSO method for the global minimum search followed by density functional theory. It is found that the global minima obtained for the neutral clusters correspond to the half-sandwich structure and those of the monoanionic clusters correspond to the boat-shaped structure. The neutral MB12 (M = Li, Na, K) can be considered as a member of the half-sandwich doped B12 clusters, and the geometrical pattern of anion MB12– (M = Li, Na, K) is a new structure that is different from other doped B12 clusters. Natural population and chemical bonding analyses reveal that the alkali metal atom-doped boron clusters MB12– are characterized as charge transfer complexes, M+B122–, resulting in symmetrically distributed chemical bonds and electrostatic interactions between cationic M+ and boron atoms. The calculated spectra indicate that MB120/– (M = Li, Na, K) has meaningful spectral features that can be compared with future experimental data. Our work enriches the varieties of geometrical structures of doped boron clusters and can provide much insight into boron nanomaterials.

Powder X-ray diffraction study on possible structural change around 550 K in β-rhombohedral boron

In this study, to investigate the possible structural change at ~550 K, the temperature dependence of powder X-ray diffraction (XRD) patterns of β-rhombohedral boron for a wide temperature range between 270 and 873 K was measured. We indexed all powder XRD patterns as β-rhombohedral boron for a whole temperature range; however, we observed that, at >550 K, the temperature dependence of the lattice parameters changed their slope. Moreover, at a temperature >600 K, we observed a drastically structural and local B12 icosahedral cluster-volume change, i.e., each icosahedral cluster-volume started to shrink and expand. Both shrinking and expansion depended on the electron deficiency and excess of B12 clusters, respectively. Moreover, the void volume started increasing at the same temperature range. Additionally, the B13 site occupancy and the total number of boron atoms at the interstitial site (B16–B20 site) showed significant temperature dependence. Therefore, our observation is an experimental validation of the interatomic hopping of boron above 550 K predicted by Hoffmann and Werheit [S. Hoffmann and H. Werheit, Solid State Sciences 14, 1572 (2012)].

Analysis of the electronic delocalization in some isoelectronic analogues of B12 doped with beryllium and/or carbon

In the current work, a new family of isoelectronic analogues to B12 is reported. The construction of this family was performed through the isoelectronic substitution principle to generate species such as B11C+, B11Be-, B10BeC, B10C22+, B10Be22- B9Be2C-, and B9BeC2+. The search for the global minimum was realized by utilizing genetic algorithms, while the induced magnetic field, electronic localization function, magnetic current densities, and multicenter aromaticity criteria were calculated to understand their electronic delocalization. Our results show that, in general, C atoms avoid hypercoordination, whereas we have found species with Be atoms located in hypercoordinated positions that are relatively stable. Our analysis of aromaticity indicates that B12 has double σ and π disk aromaticity. Mono, double or triple substitution of B by C+ or Be- reduces somewhat the aromaticity of the clusters, but less in the case of Be- substitution.

Selective capture of CO2 over N2 and CH4: B clusters and their size effects

Using density-functional theory (DFT), we investigate the selectivity of adsorption of CO2 over N2 and CH4 on planar-type B clusters, based on our previous finding of strong chemisorption of CO2 on the B10−13 planar and quasiplanar clusters. We consider the prototype B8 and B12 planar-type clusters and perform a comparative study of the adsorption of the three molecules on these clusters. We find that, at room temperature, CO2 can be separated from N2 by selective binding to the B12 cluster and not to the B8 cluster. Selective adsorption of CO2 over CH4 at room temperature is possible for both clusters. Based on our DFT-adsorption data (including also a semi-infinite Boron sheet) and the available literature-adsorption value for N2 on the planar-type B36 cluster, we discuss the selectivity trend of CO2 adsorption over N2 and CH4 with planar-cluster size, showing that it extends over sizes including B10-13 clusters and significantly larger.

High pressure modifications in amorphous boron suboxide: An ab initio study

Using constant pressure ab initio calculations, we probe the high-pressure modifications in amorphous boron suboxide (B6O) consisting of glassy boron trioxide (B2O3) and boron (B) domains up to a theoretical pressure of 100 GPa. At this pressure, the structure remains amorphous. We find a steady increase in the average coordination of both B and oxygen (O) atoms. O atoms mostly attain threefold coordination as in B2O3 glass at high pressures. On the other hand, the mean coordination number of B-atoms reaches six at high pressures and the structural changes in B-rich regions are perceived to be quite analogous to those of amorphous B. B12 clusters are found to persevere during the pressurizing process and the high-pressure modifications occur predominantly around O-atoms and the regions that connect the pentagonal pyramid-like motifs to each other. Upon pressure release, some high-pressure configurations persist in the model and another noncrystalline structure being about 10% denser than the original state is recovered, suggesting a permanent densification and a possible irreversible amorphous-to-amorphous phase transformation in B6O. The recovered network shows slightly better mechanical properties than the uncompressed model. During the compression and decompression processes, amorphous B6O remains semiconducting. The delocalization of some band tail states is seen at high pressures.

Liquid and amorphous states of boron subarsenide

AbstractAb initio molecular dynamics simulations are executed to probe the short‐range order and the electrical features of the liquid and amorphous boron subarsenide (B12As2). A drastic volume swelling of ~40% is witnessed for the liquid state, relative to the crystal. The density of the melt is found to be close to that of liquid boron. As the temperature applied is gradually decreased, the volume progressively decreases and a glass‐transition zone at around 1400 K is observed. About 14% volume expansion is perceived for the amorphous phase. Due to the drastic density (volume) difference between the liquid and amorphous forms, their atomic structure is found to be different from each other. In the liquid phase at 2500 K, the mean coordination number (CN) of B and As atoms is 4.4 and 2.5, correspondingly. During the solidification process, both average CNs steadily increase and reach values of 5.5 (B‐atom) and 4.14 (As‐atom) at 300 K. The pentagonal pyramid‐like motifs barely survive at 2500 K but during the quenching process they develop progressively and some of which lead to the formation of B12 clusters. In the amorphous state, the chain‐like and A7‐like As‐As clusters are observed. Nonetheless, the noncrystalline state is proposed to be partially similar to the crystalline structure. The liquid state shows a metallic character while the amorphous form presents a semiconducting nature having an energy band gap much smaller than that of the crystalline phase.

First principles study of structural and optical properties of [formula omitted] isomers

In this work we undertake a comprehensive numerical study of the ground state structures and optical absorption spectra of isomers of B12 cluster. Geometry optimization was performed at the coupled-cluster-singles-doubles (CCSD) level of theory, employing cc-pVDZ extended basis sets. Once the geometry of a given isomer was optimized, its ground state energy was calculated more accurately at the coupled-cluster-singles-doubles along with perturbative treatment of triples (CCSD(T)) level of theory, employing larger cc-pVTZ basis sets. Thus, our computed values of binding energies of various isomers are expected to be quite accurate. Our geometry optimization reveals eleven distinct isomers, along with their point group, and electronic ground state symmetries. We also performed vibrational frequency analysis on the three lowest energy isomers, and found them to be stable. Therefore, we computed the linear optical absorption spectra of these isomers of B12, employing large-scale multi-reference singles-doubles configuration-interaction (MRSDCI) approach, and found a strong structure-property relationship. This implies that the spectral fingerprints of the geometries can be utilized for optical detection, and characterization, of various isomers of B12. We also explored the stability of the isomer with the structure of a perfect icosahedron, with Ih symmetry. In bulk boron icosahedron is the basic structural unit, but, our vibrational frequency analysis reveals that it is unstable in the isolated form. We speculate that this instability could be due to Jahn-Teller distortion because five-fold degenerate HOMO orbitals in Ih structure are unfilled.

Ideal Nodal Line Semimetal in a Two-Dimensional Boron Bilayer

The successful experimental syntheses of two-dimensional (2D) boron allotropes with intriguing properties have stimulated great interest in searching for novel low-dimensional boron. By using high-throughput first-principles calculations, we proposed a new stable 2D boron with a bilayer structure (P6-boron), composed of the building blocks of buckled B12 cluster. We showed the possibility of experimental syntheses of P6-boron on metal substrates and proposed a strategy to pursue for P6-boron by the B12 clusters self-assembly. Specifically, P6-boron possesses a topologically nontrivial Dirac nodal line, which is protected by the mirror-reflection symmetry. Furthermore, we employed a low-energy effective k·p model to prove the existence of the nodal line solution. In addition, the topological analysis of bonding suggests that the chemical bonds of P6-boron are all covalent rather than ionic bonds found in bilayer P6/mmm boron. We expect that our findings can favor the low-dissipation high-speed nanoele...

Li2 B12 and Li3 B12 : Prediction of the Smallest Tubular and Cage-like Boron Structures.

An intriguing structural transition from the quasi-planar form of B12 cluster upon the interaction with lithium atoms is reported. High-level computations show that the lowest energy structures of LiB12 , Li2 B12 , and Li3 B12 have quasi-planar (Cs ), tubular (D6d ), and cage-like (Cs ) geometries, respectively. The energetic cost of distorting the B12 quasi-planar fragment is overcompensated by an enhanced electrostatic interaction between the Li cations and the tubular or cage-like B12 fragments, which is the main reason of such drastic structural changes, resulting in the smallest tubular (Li2 B12 ) and cage-like (Li3 B12 ) boron structures reported to date.

Li2B12 and Li3B12: Prediction of the Smallest Tubular and Cage‐like Boron Structures

AbstractAn intriguing structural transition from the quasi‐planar form of B12 cluster upon the interaction with lithium atoms is reported. High‐level computations show that the lowest energy structures of LiB12, Li2B12, and Li3B12 have quasi‐planar (Cs), tubular (D6d), and cage‐like (Cs) geometries, respectively. The energetic cost of distorting the B12 quasi‐planar fragment is overcompensated by an enhanced electrostatic interaction between the Li cations and the tubular or cage‐like B12 fragments, which is the main reason of such drastic structural changes, resulting in the smallest tubular (Li2B12) and cage‐like (Li3B12) boron structures reported to date.

Soft X-ray emission spectroscopy study of electronic structure of sodium borosilicide Na8B74.5Si17.5.

Chemical bonding state of sodium borosilicide Na8B74.5Si17.5, which is a new member of B12-cluster materials, is investigated by soft X-ray emission spectroscopy. The material is composed of B12 cluster network and characteristic silicon chains of [-Si-(Si-Si)3-Si-] connected by sp3 bonding, in which bonding distances and bonding angles are close to those in cubic Si crystal. B K-emission spectrum of the material showed a similar but a broader intensity distribution with those of B12 cluster materials of α-r-B, B4C and β-r-B. The broader intensity distribution can be due to a variation of B-B bond length in B12 cluster. The density of states (DOS) of silicon chains of [-Si-(Si-Si)3-Si-] was experimentally derived. It shows a similar energy width, and peak or shoulder structures in intensity distribution with those of L-emission spectrum of cubic Si. From comparisons between experimental spectra and corresponding calculated DOS, covalent bonding between Si chain and B12 cluster network is suggested. Those are discussed by using a theoretically calculated density of state of Na8B74.5Si17.5 by using WIEN2k code.

Metal Templates and Boron Sources Controlling Borophene Structures: An Ab Initio Study

Interlayer binding of 2D borophene phases are determined as a function of hole density (HD) and metal surfaces Cu, Ag, and Au. The Cu surface prefers formation of monolayers whereas the Au surface shows multilayer stacking. Ag surface enables formation of monolayers with higher HD and bilayers for borophenes with lower HD. The growth pattern of bilayers on metal templates are investigated using ab-initio molecular dynamic simulations. Formation of icosahedral B12 clusters and extension to sheets are also studied on Cu surface. Icosahedral sheet formation by boron atom deposition is found to be a thermodynamically unfavorable process on this surface. Thus, structure of borophene phases could also be tuned by modulating the parameters such as boron source or the metal templates, in addition to the substrate temperature and boron atom deposition rate.