The Planar CoB 18− Cluster as a Motif for Metallo‐Borophenes

MB16 - (M=Sc, Y, La): Perfect Bowl-Like Boron Clusters

The introduction of transition-metal doping has engendered a remarkable array of unprecedented boron motifs characterized by distinctive geometries and bonding, particularly those heretofore unobserved in pure boron clusters. In this study, we present a perfect (no defects) boron framework manifesting an inherently high-symmetry, bowl-like architecture, denoted as MB16 - (M=Sc, Y, La). In MB16 -, the B16 is coordinated to M atoms along the C5v-symmetry axis. The bowl-shaped MB16 - structure is predicted to be the lowest-energy structure with superior stability, owing to its concentric (2 π+10 π) dual π aromaticity. Notably, the C5v-symmetry bowl-like B16 - is profoundly stabilized through the doping of an M atom, facilitated by strong d-pπ interactions between M and boron motifs, in conjunction with additional electrostatic stabilization by an electron transfer from M to the boron motifs. This concerted interplay of covalent and electrostatic interactions between M and bowl-like B16 renders MB16 - a species of exceptional thermodynamic stability, thus making it a viable candidate for gas-phase experimental detection.

Geometric and electronic diversity of metal doped boron clusters

Being intermediate between small compounds and bulk materials, nanoparticles possess unique properties different from those of atoms, molecules, and bulk matter. In the past two decades, a combination of cluster structure prediction algorithms and experimental spectroscopy techniques was successfully used for exploration of the ground-state structures of pure and metal-doped boron clusters. The fruitfulness of this dual approach is well illustrated by the discovery of intriguing microstructures and unique physicochemical properties such as aromaticity and bond fluxionality for both boron and metal-doped boron clusters. Our review starts with an overview of geometrical configurations of pure boron clusters B_n, which are presented by planar, nanotube, bilayer, fullerene-like and core-shell structures, in a wide range ofnvalues. We consider next recent advances in studies of boron clusters doped with metal atoms paying close and thoughtful attention to modifications of geometric and electronic structures of pure boron clusters by heteroatoms. Finally, we discuss the possibility of constructing boron-based nanomaterials with specific functions from metal-boron clusters. Despite a variety of fruitful results obtained in numerous studies of boron clusters, the exploration of boron-based chemistry has not yet reached its peak. The intensive research continues in this area, and it should be expected that it brings exciting discoveries of intriguing new structures.

Construction of the Largest Metal-Centered Double-Ring Tubular Boron Clusters Based on Actinide Metal Doping

Metal doping has been considered to be an effective approach to stabilize various boron clusters. In this work, we constructed a series of largest metal-centered double-ring tubular boron clusters An@B₂₄ (An = Th, Pa, Pu, and Am). Extensive global minimum structural searches combined with density functional theory predicted that the global minima of An@B₂₄ (An = Th, Pu, and Am) are double-ring tubular structures. Formation energy analysis indicates that these boron clusters are highly stable, especially for Th@B₂₄ and Pa@B₂₄. Detailed bonding analysis shows that the significant stability of An@B₂₄ is determined by the covalent character of the An-B bonding, which stems from the interactions of An 5f and 6d orbitals and B 2p orbitals. These results show that actinide metal doping is a feasible route to construct stable large metal-centered double-ring tubular boron clusters, offering the possibility to design boron nanomaterials with special physiochemical properties.

Exploring the structure and electronic properties of germanium doped boron clusters using density functional theory based global optimization method

Density functional theory calculations to investigate the effect of single and double germanium atom doping on the geometric structure and electronic properties of boron clusters with 10 to 20 atoms.

Theoretical probing of twenty-coordinate actinide-centered boron molecular drums

The exploration of metal-doped boron clusters has a great significance in the design of high coordination number (CN) compounds. Actinide-doped boron clusters are probable candidates for achieving high CNs. In this work, we systematically explored a series of actinide metal atom (U, Np, and Pu) doped B₂₀ boron clusters An@B₂₀ (An = U, Np, and Pu) by global minimum structural searches and density functional theory (DFT). Each An@B₂₀ cluster is confirmed to be a twenty-coordinate complex, which is the highest CN obtained in the chemistry of actinide-doped boron clusters so far. The predicted global minima of An@B₂₀ are tubular structures with actinide atoms as centers, which can be considered as boron molecular drums. In An@B₂₀, U@B₂₀ has a relatively high symmetry of C₂, while both Np@B₂₀ and Pu@B₂₀ exhibit C₁ symmetry. Extensive bonding analysis demonstrates that An@B₂₀ has σ and π delocalized bonding, and the U-B bonds possess a relatively higher covalency than the Np-B and Pu-B bonds, resulting in the higher formation energy of U@B₂₀. Therefore, the covalent character of An-B bonding may be crucial for the formation of these high CN actinide-centered boron clusters. These results deepen our understanding of actinide metal doped boron clusters and provide new clues for developing stable high CN boron-based nanomaterials.

Fully Boron-Sheet-Based Field Effect Transistors from First-Principles: Inverse Design of Semiconducting Boron Sheets

High-performance two-dimensional (2D) field effect transistors (FETs) have a broad application prospect in future electronic devices. The lack of an ideal material system, however, hinders the breakthrough of 2D FETs. Recently, phase engineering offers a promising solution, but it requires both semiconducting and metallic phases of materials. Here we suggest borophenes as ideal systems for 2D FETs by theoretically searching semiconducting phases. Using multiobjective differential optimization algorithms implemented in the IM²ODE package and the first-principles calculations, we have successfully identified 16 new semiconducting borophenes. Among them, the B₁₂-1 borophene is the most stable semiconducting phase, whose total energy is lower than any other known semiconducting borophenes. By considering not only the band alignments but also the lattice matches between semiconducting and metallic borophenes, we then have theoretically proposed several device models of fully boron-sheet-based 2D FETs. Our work provides beneficial ideas and attempts for discovering novel borophene-based 2D FETs.

Observation of Transition-Metal-Boron Triple Bonds in IrB2 O- and ReB2 O. Angew Chem Int Ed Engl 2020;59:15260-15265. [PMID: 32424965 DOI: 10.1002/anie.202006652]

Multiple bonds between boron and transition metals are known in many borylene (:BR) complexes via metal d_π →BR back-donation, despite the electron deficiency of boron. An electron-precise metal-boron triple bond was first observed in BiB₂ O^- [Bi≡B-B≡O]^- in which both boron atoms can be viewed as sp-hybridized and the [B-BO]^- fragment is isoelectronic to a carbyne (CR). To search for the first electron-precise transition-metal-boron triple-bond species, we have produced IrB₂ O^- and ReB₂ O^- and investigated them by photoelectron spectroscopy and quantum-chemical calculations. The results allow to elucidate the structures and bonding in the two clusters. We find IrB₂ O^- has a closed-shell bent structure (C_s , ¹ A') with BO^- coordinated to an Ir≡B unit, (^- OB)Ir≡B, whereas ReB₂ O^- is linear (C_∞v , ³ Σ^- ) with an electron-precise Re≡B triple bond, [Re≡B-B≡O]^- . The results suggest the intriguing possibility of synthesizing compounds with electron-precise M≡B triple bonds analogous to classical carbyne systems.

High-Resolution Photoelectron Imaging of IrB3 - : Observation of a π-Aromatic B3 + Ring Coordinated to a Transition Metal

In a high-resolution photoelectron imaging and theoretical study of the IrB₃ ^- cluster, two isomers were observed experimentally with electron affinities (EAs) of 1.3147(8) and 1.937(4) eV. Quantum calculations revealed two nearly degenerate isomers competing for the global minimum, both with a B₃ ring coordinated with the Ir atom. The isomer with the higher EA consists of a B₃ ring with a bridge-bonded Ir atom (C_s , ² A'), and the second isomer features a tetrahedral structure (C_3v , ² A₁ ). The neutral tetrahedral structure was predicted to be considerably more stable than all other isomers. Chemical bonding analysis showed that the neutral C_3v isomer involves significant covalent Ir-B bonding and weak ionic bonding with charge transfer from B₃ to Ir, and can be viewed as an Ir-(η³ -B₃ ⁺ ) complex. This study provides the first example of a boron-to-metal charge-transfer complex and evidence of a π-aromatic B₃ ⁺ ring coordinated to a transition metal.

Structural and electronic properties of MB22− (M = Na, K) clusters: tubular boron versus quasi-planar boron forms

Electron deficiency of boron atom has led to the abundant chemical properties of boron clusters, such as intriguing structures, unique multi-center bonding and electronic properties, as well as the structural evolution from planar to three-dimensional forms.

TGMin: An efficient global minimum searching program for free and surface-supported clusters

In this article, we introduce an efficient global-minimum structural search program named Tsinghua Global Minimum 2 (TGMin-2), which is the successor of the original TGMin algorithm that was developed in our group in 2011. We have introduced a number of new features and improvements into TGMin-2, including a symmetric structure generation algorithm that can produce good initial seeds for small- and medium-size clusters, the duplicated structure identification algorithm, and the improved structure adaption algorithm that was implemented in the original TGMin code. To predict the simulated photoelectron spectrum (PE spectrum) automatically, we also implemented a standalone program named AutoPES (Auto Photoelectron Spectroscopy), which can be used to simulate PE spectra and compare them with experimental results automatically. We have demonstrated that TGMin-2 and AutoPES are powerful tools for studying free and surface-supported molecules, clusters, and nanoclusters. © 2018 Wiley Periodicals, Inc.

Lithium doped tubular structure in LiB20 and LiB20-: a viable global minimum

We present a strategy by which the stability of tubular boron clusters can be significantly enhanced by doping the B20 cluster with a lithium atom. High-level quantum chemical calculations showed that the lowest energy structures of LiB20 and LiB20- are tubular structures with D10d symmetry, in which the lithium atom is located at the center of the tubular structure. Chemical bonding analysis revealed that the high-symmetry tubular boron clusters are characterized as charge transfer complexes (Li+B20- and Li+B202-), resulting in double aromaticity with delocalized π + σ bonding and strong electrostatic interactions between cationic Li+ and tubular boron motifs with twenty Li-B interactions. The unique bonding pattern of the LiB20 and LiB20- species provides a key driving force to stabilize tubular structures over quasi-planar structures, suggesting that electrostatic interactions resulting from alkali metals might unveil a new clue to the structural evolution of boron clusters.

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 (C_s ), tubular (D_6d ), and cage-like (C_s ) 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.

Deciphering chemical bonding in BnHn2−(n = 2–17): flexible multicenter bonding

Deciphering flexible multicenter bonding incloso-borane dianions B_nH_n²⁻.