Icosahedral B12 Research Articles

Superatom-assembled boranes, carboranes, and low-dimensional boron nanomaterials based on aromatic icosahedral B12 and C2B10

Superatom-assembled boranes, carboranes, and low-dimensional boron nanomaterials based on aromatic icosahedral B12 and C2B10

Large-size gold–aluminum alloy cluster Al12Au60 stabilized by an encapsulating B12 icosahedron: a first-principles study

The investigation of novel clusters incorporating gold (Au) has attracted increasing attention due to their intriguing architecture and feasibility of experimental synthesis. In this study, a large-size gold–aluminum alloy cluster with icosahedral B12 as its core, specifically a B12@Al12Au60 cluster, is proposed and demonstrated to have remarkable stability as ascertained through first-principles calculations. The core–shell assembly, B12@Al12Au60, exhibiting I symmetry, is characterized by the incorporation of an icosahedral B12 motif within the outer shell of the Al12Au60 framework. By thorough analysis encompassing vibrational frequency and molecular dynamics simulations, the structural stability of the core–shell B12@Al12Au60 is investigated. The electronic characteristics are probed through adaptive natural density partitioning analysis, revealing the presence of 66 multi-center two-electron σ bonds distributed across the entirety of the core–shell configuration. Furthermore, scrutiny of distinct dimeric configurations composed of core–shell B12@Al12Au60 underscores their relative autonomy and potential prospects for applications within cluster-assembled materials.

B92: a complete coating icosahedral B12 core-shell structure.

Using first-principles calculations, this study unveils a spherically aromatic core-shell B12@B80 structure featuring a B12 icosahedral core, which is the smallest complete coating icosahedral B12 core-shell Bn cluster to date. Detailed orbital and bonding analyses reveal that the icosahedral B12 core exhibits prominent superatomic behavior with the electronic configuration 1S21P61D101F8.

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.

Highly symmetrical B12@Mg20C12 with icosahedral B12 motif: A potential hydrogen storage medium

A highly symmetrical core–shell Ih B12@Mg20C12 structure containing icosahedral B12 motif has been proposed in the framework of density functional theory. The core–shell B12@Mg20C12 structure has good kinetic and thermodynamic stability, which is verified by vibrational frequency analysis and molecular dynamics simulations, respectively. The analysis of the electronic structure shows that multiple atoms are connected into a whole by multi-center two-electron σ bonds, which is also the fundamental reason for the structure stability. Raman and photoelectron spectroscopy are simulated theoretically to provide characterizations for future experiments. The core–shell B12@Mg20C12 structure is a potential hydrogen storage material, which can absorb about 72 H2 molecules with a hydrogen capacity as high as 16.0 wt%.

Pivotal role of the B12-core in the structural evolution of B52-B64 clusters.

An icosahedral B12 cage is a basic building block of various boron allotropes, and it also plays a vital role in augmenting the stability of fullerene-like boron nanoclusters. However, the evolution of compact core-shell structures is still a puzzle. Using a genetic algorithm combined with density functional theory calculations, we have performed a global search for the lowest-energy structures of Bn clusters with n = 52-64, which reveals that bilayer and core-shell motifs frequently alternate as the ground state. Their structural stability is assessed, and the competition mechanism between various patterns is also elucidated. More interestingly, an unprecedented icosahedral B12-core half-covered structure is identified at B58, which bridges the gap between the smallest core-shell B4@B42 and the complete core-shell B12@B84 cluster. Our findings provide valuable insights into the bonding pattern and growth behavior of medium-sized boron clusters, which facilitate the experimental synthesis of boron nanostructures.

Strong Binding of Noble Gases to [B12X11]-: A Theoretical Study.

We systematically explore the stability and properties of [B12X11NG]- adducts resulting from the binding of noble gas atoms to anionic [B12X11]- clusters in the gas phase of mass spectrometers. [B12X11]- can be obtained by stripping one X- off the icosahedral closo-dodecaborate dianion [B12X12]2-. We study the binding of the noble gas atoms He, Ne, Ar, Kr, and Xe to [B12X11]- with substituents X = F, Cl, Br, I, and CN. While He cannot be captured by these clusters and Ne only binds at low temperatures, the complexes with the heavier noble gas atoms Ar, Kr, and Xe show appreciable complexation energies and exceed 1 eV at room temperature in the case of [B12(CN)11Xe]-. The predicted B-NG equilibrium distance in the complexes with Ar, Kr, and Xe is only 0.10-0.25 Å longer than the sum of the covalent radii of the two corresponding atoms, and a significant charge transfer from the noble gas atom to the icosahedral B12 cage is observed.

B111, B112, B113, and B114: The most stable core-shell borospherenes with an icosahedral B12 core at the center exhibiting superatomic behaviors

Boron allotropes are known to be predominately constructed by icosahedral B12 cages, while icosahedral-B12 stuffing proves to effectively improve the stability of fullerene-like boron nanoclusters in the size range between B98–B102. However, the thermodynamically most stable core-shell borospherenes with a B12 icosahedron at the center still remains unknown. Based on the structural motif of D5h C70 and extensive first-principles theory calculations, we predict herein the high-symmetry C5v B111+ (3) which satisfies the Wade’s n+1 and n+2 skeletal electron counting rules exactly and the approximately electron sufficient Cs B111 (4), Cs B112 (5), Cs B113 (6), and Cs B114 (7) which are the most stable neutral core-shell borospherenes with a B12 icosahedron at the center reported to date in the size range between B68–B130, with Cs B112 (5) being the thermodynamically most favorite species in the series. Detailed orbital and bonding analyses indicate that these spherically aromatic species all contain a negatively charged icosahedral B122− core at the center which exhibits typical superatomic behaviors in the electronic configuration of 1S21P61D101F8, with its dangling valences saturated by twelve radial B-B 2c-2e σ bonds between the B12 inner core and the B70 outer shell. The infrared (IR) and Raman spectra of the concerned species are computationally simulated to facilitate their future characterizations.

Boranes: The Boron Subhydride B104.67H3 with a Distorted β-Boron Crystal Structure.

A single crystal of the boron subhydride B104.67(4)H3 was serendipitously obtained while attempting to synthesize β-boron. An accurate crystal structure analysis revealed a distorted β-boron framework with the noncentrosymmetric space group R3m. We have found one interstitial site occupied by boron. The site related by inversion remains empty. The distortions of the framework result in ideal environments for the interstitial boron atom, and for the three hydrogen atoms at bridging positions between icosahedral B12 groups, they result in ideal B-H distances of 1.33 Å. B104.67(4)H3 is a borane with the lowest amount of hydrogen recorded to date, and it is the first compound with a noncentrosymmetrically distorted β-boron framework.

Study of amorphous boron carbide (a-BxC) materials using Molecular Dynamics (MD) and Hybrid Reverse Monte Carlo (HRMC)

We present a computational study of amorphous boron carbide (a-BxC) models using Molecular Dynamics (MD) studied with Stillinger-Weber (SW) and ReaxFF potential. The atomic structure factor (S(Q)), radial distribution function (RDF) and bond lengths comparison with other experimental and ab initio models show that a random arrangement of icosahedra (B12, B11C) interconnected by chains (CCC, CBC) are present in a-BxC. Subsequently, Hybrid Reverse Monte Carlo (HRMC) method is used to reconstruct a-BxC structures. The existing SW potential parameters of Boron are optimized for the α-rhombohedral (Icosahedral B12) boron structure using potential energy minimization and incorporated into HRMC. The a-BxC modeled from MD simulation is used as a sample for experimental input parameters like RDF, S(Q), coordination environments (CO), bond angle distribution (BAD) and bond length (BL) to guide initial configuration and simulation in HRMC. An accurate agreement of structural information between HRMC and MD generated models was found.

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.

The effects of halogen elements on the opening of an icosahedral B12 framework.

The fully halogenated or hydrogenated B12X122- (X = H, F, Cl, Br and I) clusters are confirmed to be icosahedral. On the other hand, the bare B12 cluster is shown to have a planar structure. A previous study showed that a transformation from an icosahedron to a plane happens when 5 to 7 iodine atoms are remained [P. Farràs et al., Chem. - Eur. J. 18, 13208-13212 (2012)]. Later, the transition was confirmed to be seven iodine atoms based on an infrared spectroscopy study [M. R. Fagiania et al., Chem. Phys. Lett. 625, 48-52 (2015)]. In this study, we investigated the effects of different halogen atoms on the opening of the B12 icosahedral cage by means of density functional theory calculations. We found that the halogen elements do not have significant effects on the geometries of the clusters. The computed infrared (IR) spectra show similar representative peaks for all halogen doped clusters. Interestingly, we found a blue-shift in the IR spectra with the increase in the mass of the halogen atoms. Further, we compared the Gibbs free energies at different temperatures for different halogen atoms. The results show that the Gibbs free energy differences between open and close structures of B12X7- become larger when heavier halogen atoms are presented. This interesting finding was subsequently investigated by the energy decomposition analysis.

Charge Transfer and Fractional Bonds in Stoichiometric Boron Carbide

Based on an electron-density study using high-resolution single-crystal synchrotron X-ray diffraction data, a new bonding model for boron carbide (B13C2) has been proposed that is consistent with its chemical and physical properties. Analysis of the electron density with the aid of Bader’s quantum theory of atoms in molecule reveals an unprecedented electron-deficient inter-cluster bond in B13C2, whereby charge transfer between the constituent structural units of B13C2, namely from the CBC chains to the icosahedral B12 clusters, occurs. The bonding model explains why boron carbide and related boron-rich materials preserve the same crystal structure over a wide range of compositions, and indicates how the properties of boron carbide can be tuned for improved applications.

X-ray photoelectron spectroscopy analysis of boron defects in silicon crystal: A first-principles study

We carried out a comprehensive study on the B 1s core-level X-ray photoelectron spectroscopy (XPS) binding energies and formation energies for boron defects in crystalline silicon by first-principles calculation with careful evaluation of the local potential boundary condition for the model system using the supercell corresponding to 1000 Si atoms. It is reconfirmed that the cubo-octahedral B12 cluster in silicon crystal is unstable and exists at the saddle point decaying to the icosahedral and S4 B12 clusters. The electrically active clusters without any postannealing of ion-implanted Si are identified as icosahedral B12 clusters. The experimentally proposed threefold coordinated B is also identified as a ⟨001⟩B-Si defect. For an as-doped sample prepared by plasma doping, the calculated XPS spectra for complexes consisting of vacancies and substitutional B atoms are consistent with the experimental spectra. It is proposed that, assuming that the XPS peak at 187.1 eV is due to substitutional B (Bs), the experimental XPS peaks at 187.9 and 186.7 eV correspond to interstitial B at the H-site and ⟨001⟩B-Si defects, respectively. In the annealed samples, the complex of Bs and interstitial Si near the T-site is proposed as a candidate for the experimental XPS peak at 188.3 eV.

Thermal Decomposition of Anhydrous Alkali Metal Dodecaborates M2B12H12 (M = Li, Na, K)

Metal dodecaborates M2/nB12H12 are regarded as the dehydrogenation intermediates of metal borohydrides M(BH4)n that are expected to be high density hydrogen storage materials. In this work, thermal decomposition processes of anhydrous alkali metal dodecaborates M2B12H12 (M = Li, Na, K) synthesized by sintering of MBH4 (M = Li, Na, K) and B10H14 have been systematically investigated in order to understand its role in the dehydrogenation of M(BH4)n. Thermal decomposition of M2B12H12 indicates multistep pathways accompanying the formation of H-deficient monomers M2B12H12−x containing the icosahedral B12 skeletons and is followed by the formation of (M2B12Hz)n polymers. The decomposition behaviors are different with the in situ formed M2B12H12 during the dehydrogenation of metal borohydrides.

Two-Dimensional Boron Monolayers Mediated by Metal Substrates.

Two-dimensional (2D) materials, such as graphene and boron nitride, have specific lattice structures independent of external conditions. In contrast, the structure of 2D boron sensitively depends on metal substrate, as we show herein using the cluster expansion method and a newly developed surface structure-search method, both based on first-principles calculations. The preferred 2D boron on weaker interacting Au is nonplanar with significant buckling and numerous polymorphs as in vacuum, whereas on more reactive Ag, Cu, and Ni, the polymorphic energy degeneracy is lifted and a particular planar structure is found to be most stable. We also show that a layer composed of icosahedral B12 is unfavorable on Cu and Ni but unexpectedly becomes a possible minimum on Au and Ag. The substrate-dependent 2D boron choices originate from a competition between the strain energy of buckling and chemical energy of electronic hybridization between boron and metal.

Symmetry and topology codes of cluster self-assembly for icosahedral structures of the NaZn13-cF112 and TRB66-cF1944 family

Algorithms for combinatorial topology analysis have been developed that allow restoring symmetry and topology codes (program) of crystal structure cluster self-assembly for intermetallic systems. The analysis method is based on the determination of the chemical composition and structure of an intermetallic cluster-precursor and the construction of a basic 3D net of the structure in the form of a graph with the nodes corresponding to the positions of the centers of gravity of the cluster-precursors. The cluster self-assembly of icosahedral structures was modeled for the family of NaZn13-cF112 and TRB66-cF1944 structures, in which the unit cubic cF-cells contain 112 atoms (8 · NaZn13, V = 1849 A3) and 1608 atoms (24 · YB66, V = 23440 A3), respectively. The topological type of the basic 3D net in the NaZn13 and TRB66 structures (with space group Fm-3c) corresponds to the primitive 3D net P c (Pm–3m, cP1) with c.n. = 6. The cluster-precursor of the NaZn13 structure is an icosahedral cluster Zn@Zn12. The cluster-precursor of the TRB66 structure containing 156 B atoms comprises 13 icosahedrons (B12)13, with the icosahedron B12 in the center of the supracluster linked to the 12 icosahedrons forming an icosahedral shell. The Zn13 and (B12)13B cluster-precursors occupy positions 8b in the crystal structures with the highest crystallographically possible symmetry of m3. The symmetry and topology code of the processes of self-assembly of 3D structures from the nanocluster-precursors—primary chain → microlayer → micronetwork—has been completely reconstructed. The large metal atoms A (with c.n. = 24) are spacers in the AZn13 structures, which occupy voids in the 3D nets from the Be13, Co13, Cu13, Zn13, and Cd13 icosahedrons. The atoms spacers in the TRB66 structures (3 TR and 39 B, TR = Y, Sm, Gd–Lu) statistically occupy the large voids in the 3D nets. The TRB66 crystal structure can be obtained from the NaZn13 by the replacement (decoration) of all 13 Zn atoms with 13 icosahedral B12 clusters; and the system of bonds between the structural units is completely conserved in the process.

Next generation of the self-consistent and environment-dependent Hamiltonian: Applications to various boron allotropes from zero- to three-dimensional structures.

An upgrade of the previous self-consistent and environment-dependent linear combination of atomic orbitals Hamiltonian (referred as SCED-LCAO) has been developed. This improved version of the semi-empirical SCED-LCAO Hamiltonian, in addition to the inclusion of self-consistent determination of charge redistribution, multi-center interactions, and modeling of electron-electron correlation, has taken into account the effect excited on the orbitals due to the atomic aggregation. This important upgrade has been subjected to a stringent test, the construction of the SCED-LCAO Hamiltonian for boron. It was shown that the Hamiltonian for boron has successfully characterized the electron deficiency of boron and captured the complex chemical bonding in various boron allotropes, including the planar and quasi-planar, the convex, the ring, the icosahedral, and the fullerene-like clusters, the two-dimensional monolayer sheets, and the bulk alpha boron, demonstrating its transferability, robustness, reliability, and predictive power. The molecular dynamics simulation scheme based on the Hamiltonian has been applied to explore the existence and the energetics of ∼230 compact boron clusters BN with N in the range from ∼100 to 768, including the random, the rhombohedral, and the spherical icosahedral structures. It was found that, energetically, clusters containing whole icosahedral B12 units are more stable for boron clusters of larger size (N > 200). The ease with which the simulations both at 0 K and finite temperatures were completed is a demonstration of the efficiency of the SCED-LCAO Hamiltonian.

The debut of all-boron fullerene

Boron is the fifth element and next to carbon in the periodic table of the elements, but boron has been researched less than its neighbor carbon. Borax sourced from a natural boronrich mine in Yamdrok Lake, Tibet, China, has been used as a fusion agent to make glass from ancient times. Elemental boron, however, was elusive until 1808 when it was prepared from electrolysis of melted boron trioxide or by reducing boric acid with potassium. Structures of elemental boron include an icosahedral (Ih) B12 motif connected in an ordered manner, as exemplified by α-rhombohedral boron (Fig. 1a). The dangling bonds in each Ih-B12 unit can be saturated by hydrogen to produce borane species. In stark contrast to the ubiquitous Ih-B12 unit in elemental boron allotropes and boranes, a different B12 all-boron clusterwith aC3v-symmetric planar structure that resembles a solid disk with three boron atoms in the center surrounded by a peripheral ring of boron atoms has also been observed (Fig. 1b) [1]. With six delocalized π electrons that exhibit ‘disk delocalization’, the planar B12 cluster is analogous to benzene with its wellknown cyclic delocalization. Bn clusters adopt 2D planar or quasi-planar structures even up to n = 36 [2]. Because of their diverse set of structural and bonding characteristics, scientists believe that boron and carbon form a set of complementary chemical systems and have long been fascinated with whether or not structures such as cage-like all-boron clusters are as prevalent as all-carbon fullerenes. A series of all-boron cage configurations stabilized by three-center Figure 1. The structures of all-boron clusters (B12 and B40). (a) Icosahedral B12 motifs bound by threecenter two-electronσ bonds (indicated by dashed lines) to form a B12 layer inα-rhombohedral boron; (b) Top and side views of a C3v-symmetric B12 cluster; (c) Top and side views of Cs-symmetric B40 with two adjacent hexagonal holes; (d) Top and side views of a neutral B40 cluster with two hexagonal and four heptagonal holes. This figure was redrawn according to the coordinates of a B40 cluster provided in the supplementary information of [5].

Facile synthesis of anhydrous alkaline earth metal dodecaborates MB12H12 (M = Mg, Ca) from M(BH4)2.

Metal dodecaborates M2/nB12H12 are among the dehydrogenation intermediates of metal borohydrides M(BH4)n with a high hydrogen density of approximately 10 mass%, the latter is a potential hydrogen storage material. There is therefore a great need to synthesize anhydrous M2/nB12H12 in order to investigate the thermal decomposition of M2/nB12H12 and to understand its role in the dehydrogenation and rehydrogenation of M(BH4)n. In this work, anhydrous alkaline earth metal dodecaborates MB12H12 (M = Mg, Ca) have been successfully synthesized by sintering M(BH4)2 (M = Mg, Ca) and B10H14 in a stoichiometric molar ratio of 1 : 1. Thermal decomposition of MB12H12 shows multistep pathways with the formation of H-deficient monomers MB12H12-x containing icosahedral B12 skeletons and is followed by the formation of (MByHz)n polymers. Comparison of the thermal decomposition of MB12H12 and M(BH4)2 suggests different behaviours of the anhydrous MB12H12 and those formed from the decomposition of M(BH4)n.