Structure evolution of chromium-doped boron clusters: toward the formation of endohedral boron cages

Size effects and electronic properties of zinc-doped boron clusters Zn B n (n = 1-15)

CONTEXT

To gain a deeper understanding of zinc-doped boron clusters, theoretical calculations were performed to investigate the size effects and electronic properties of zinc-doped boron clusters. The study of the electronic properties, spectral characteristics, and geometric structures of Zn B n (n = 1-15) is of great significance in the fields of semiconductor materials science, material detection, and improving catalytic efficiency. The results indicate that Zn B n (n = 1-15) clusters predominantly exhibit planar or quasi-planar structures, with the Zn atom positioned in the outer regions of the B n framework. The second stable structure of Zn B 3 is a three-dimensional configuration, indicating that the structures of zinc-doped boron clusters begin to convert from the planar or quasi-planar structures to the 3D configurations. The second low-energy structure of Zn B 15 is a novel configuration. Relative stability analyses show that the Zn B 12 has better chemical stability than other clusters with a HOMO-LUMO gap of 2.79 eV. Electric charge analysis shows that part electrons on zinc atoms are transferred to boron atoms, and electrons prefer to cluster near the B n framework. According to the electron localization function, it gets harder to localize electrons as the equivalent face value drops, and it's challenging to see covalent bond formation between zinc and boron atoms. The spectrograms of Zn B n (n = 1-15) exhibit distinct properties and notable spectral features, which can be used as a theoretical basis for the identification and confirmation of boron clusters doped with single-atom transition metals.

METHODS

The calculations were performed using the ABCluster global search technique combined with density functional theory (DFT) methods. The selected low-energy structures were subjected to geometric optimization and frequency calculations at the PBE0/6-311 + G(d) level to ensure structural stability and eliminate any imaginary frequencies. To acquire more precise relative energies, we performed single-point energies calculations for the low-lying isomers of Zn B n (n = 1-15) at the CCSD(T)/6-311 + G(d)//PBE0/6-311 + G(d) level of theory. All calculations were performed using Gaussian 09 software. To facilitate analysis, we utilized software tools such as Multiwfn, and VMD.

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.

Planar Elongated B12 Structure in M3B12 Clusters (M = Cu-Au)

Here, it is shown that the M₃B₁₂ (M = Cu-Au) clusters' global minima consist of an elongated planar B₁₂ fragment connected by an in-plane linear M₃ fragment. This result is striking since this B₁₂ planar structure is not favored in the bare cluster, nor when one or two metals are added. The minimum energy structures were revealed by screening the potential energy surface using genetic algorithms and density functional theory calculations. Chemical bonding analysis shows that the strong electrostatic interactions with the metal compensate for the high energy spent in the M₃ and B₁₂ fragment distortion. Furthermore, metals participate in the delocalized π-bonds, which infers an aromatic character to these species.

Quasi-planar Co atom-doped boron cluster: CoB192

PURPOSE AND METHODS

A global search for the lowest energy structure of CoB₁₉^2- clusters was conducted.  RESULTS: Its ground state is a quasi-planar structure with the Co atom surrounded by a B₈ ring. The central Co atom has an oxidation state of +1 with d⁸ electron configuration. The wave function analysis showed that the Co-B interaction is not a covalent bond. The bonding strength of peripheral B-B bonds is stronger than that of inner ones. The inner B₈ ring bonds with outer boron atoms via σ- and π-type bonds.

CONCLUSION

CoB₁₉^2- shows remarkable aromatic character.

Structural transformations in boron clusters induced by metal doping

In the last decades, experimental techniques in conjunction with theoretical analyses have revealed the surprising structural diversity of boron clusters. Although the 2D to 3D transition thresholds are well-established, there is no certainty about the factors that determine the geometry adopted by these systems. The structural transformation induced by doping usually yields a minimum energy structure with a boron skeleton entirely different from that of the bare cluster. This review summarizes those clusters no larger than 40 boron atoms where one or two dopants show a radical transformation of the structure. Although the structures of these systems are not easy to predict, they often adopt familiar shapes such as umbrella-like, wheel, tubular, and cages in various cases.

Tuning of Structure Evolution and Electronic Properties through Palladium-Doped Boron Clusters: PdB16 as a Motif for Boron-Based Nanotubes

Transition metal-doped electronic deficiency boron clusters have led to a vast variety of electronic bonding properties in chemistry and materials science. We have determined the ground state structures of PdB_n^0/- (n = 10-20) clusters by performing CALYPSO search and density functional theory (DFT) optimization. The identified lowest energy structures for both neutral and anionic Pd-doped boron clusters follow the structure evolution from two dimensional (2D) planar configurations to 3D distorted Pd-centered drum-like or tubular structures. Photoelectron spectra are simulated by time-dependent DFT theoretical calculations, which is a powerful method to validate our obtained ground-state structures. More interestingly, two "magic" number clusters, PdB₁₂ and PdB₁₆, are found with enhanced stability in the middle size regime studied. Subsequently, molecular orbital and adaptive natural density partitioning analyses reveal that the high stability of the PdB₁₆ cluster originates from doubly σ π aromatic and bonding interactions of d-type atomic orbitals of the Pd atom with tubular B₁₆ units. The tubular C_8v PdB₁₆ cluster, with robust relative stability, is an ideal embryo for forming finite and infinite nanotube nanomaterials.

A quasi-plane IrB18− cluster with high stability

A quasi-plane anionic IrB₁₈⁻ cluster with high stability is uncovered by a CALYPSO structural search method.

Theoretical investigation of perfect fullerene-like borospherene Ih-B20 protected by alkaline earth metal: multi-layered spherical electride molecules as electric field manipulated second-order nonlinear optical switches

A perfect fullerene-like borospherene B₂₀ with 12 B₅ rings stabilized in the electride molecule (Mg²⁺)₁₂&B₂₀¹⁸⁻ + 6e⁻.

Probing the structural evolution, electronic and spectral properties of beryllium doped magnesium and its ion clusters

Beryllium doped small-sized magnesium and its ion clusters are fully studied in this work.

Evolutionary search for (M©B16)Q (M = Sc-Ni; Q = 0/-1) clusters: bowl/boat vs. tubular shape

Herein, using universal structure predictor: evolutionary xtallography (USPEX) method, followed by density functional theory (DFT) calculations, we performed global searches for the most stable structures of (M©B₁₆)^Q (M = Sc, Ti, V, Cr, Mn, Fe, Co, Ni; Q = 0, -1) clusters. It was found that the obtained ground-state structures of (M©B₁₆)^Q clusters exhibited a distinct structural evolution as M changed from V to Ni: from bowl-shaped, to boat-shaped, to an M-centered tubular structure named wheel-shaped, to drum-shaped (the metal atom was adsorbed on top of the cross section of the B₁₆ species). Our analysis shows that hyper-coordination and the size of the metal atom are two competing factors determining the relative stability and topological properties of the (M©B₁₆)^0/-1 clusters, resulting in unprecedented structures for Sc, Ti, and Ni-doped clusters. The calculated binding energies for these new configurations are even larger than those of the previously synthesized B₁₆^-1, (Mn©B₁₆)^-1, and (Co©B₁₆)^-1 clusters, indicating their very good stability and possible experimental synthesis. A net charge transfer from the metal atom to the boron moiety occurs for all clusters, indicating that electrostatic interactions play an important role in the stability of these materials. Finally, the Sc©M₁₆ and Ti©B₁₆ clusters exhibit not only excellent thermal stability but also large first hyper-polarizability. Hence, they are expected to be potential innovative candidates for excellent electro-optical materials.

Probing the structures and bonding of size-selected boron and doped-boron clusters

Because of their interesting structures and bonding and potentials as motifs for new nanomaterials, size-selected boron clusters have received tremendous interest in recent years. In particular, boron cluster anions (Bn-) have allowed systematic joint photoelectron spectroscopy and theoretical studies, revealing predominantly two-dimensional structures. The discovery of the planar B36 cluster with a central hexagonal vacancy provided the first experimental evidence of the viability of 2D borons, giving rise to the concept of borophene. The finding of the B40 cage cluster unveiled the existence of fullerene-like boron clusters (borospherenes). Metal-doping can significantly extend the structural and bonding repertoire of boron clusters. Main-group metals interact with boron through s/p orbitals, resulting in either half-sandwich-type structures or substitutional structures. Transition metals are more versatile in bonding with boron, forming a variety of structures including half-sandwich structures, metal-centered boron rings, and metal-centered boron drums. Transition metal atoms have also been found to be able to be doped into the plane of 2D boron clusters, suggesting the possibility of metalloborophenes. Early studies of di-metal-doped boron clusters focused on gold, revealing ladder-like boron structures with terminal gold atoms. Recent observations of highly symmetric Ta2B6- and Ln2Bn- (n = 7-9) clusters have established a family of inverse sandwich structures with monocyclic boron rings stabilized by two metal atoms. The study of size-selected boron and doped-boron clusters is a burgeoning field of research. Further investigations will continue to reveal more interesting structures and novel chemical bonding, paving the foundation for new boron-based chemical compounds and nanomaterials.