Electronic structure, stability, and oxidation of boron-magnesium clusters and cluster solids

Endohedral boron-doped scandium clusters BmScn-m+/0 (m = 2-3, n = 3-13): triangular - linear rearrangement of the B3 dopant

A theoretical investigation, employing density functional theory with the PBE functional and the Def2-TZVP basis set, comprehensively explores the geometric and electronic structures and properties of the boron doped scandium clusters BmScn-m+/0 with m = 2-3 and n = 3-13. Introduction of B atoms significantly enhances the stability of the resulting clusters with respect to the initial counterparts. As the number of B atoms increases, the stability of the doped clusters improves, following the order: B3Scn-3+/0 > B2Scn-2+/0 > BScn-1+/0 > Scn+/0. Notably, the B2@Sc8 cluster represents the smallest fully endohedral doubly doped cage, and the B3@Sc10 is the smallest fully endohedral triply doped cage reported to date. The size with 8 Sc atoms plays a crucial role in the structural evolution of both doubly doped B2Scn-2+/0 and triply doped B3Scn-3+/0 series. For the doubly doped species, this size marks an exohedral-to-endohedral transition, while in the triply doped species, it marks an interconversion of the B3 dopant from a triangular to a linear arrangement. In the triangular B3 trimer, the electron and charge distribution are evenly shared among the three B atoms, whereas in the linear B3 trimer, these distributions are unequal. Additionally, the geometric and electronic structures of the linear-B3 doped B3@Sc8 can serve as basic building blocks for the construction of larger clusters.

Structural and spectral properties of Gas-phase FMgn (n = 2-20) clusters based on DFT

Structure, stability, electronic structure, spectroscopy and chemical bonding properties of a fluorine atom doped gas-phase small to medium-sized magnesium clusters, FMgn (n = 2-20), systematically investigated by CALYPSO software together with density functional theory (DFT). Structural calculations showed that FMgn has a structural diversity which is rarely reported in other magnesium-based clusters before. F atoms were always located in the outer layer of the Mgn host clusters and only two or three Mg atoms surround it. FMg18 was revealed to be supposed to have robust relative stability. Charge transfer and density of states were calculated for analyzing the electronic structure characteristics. Theoretical calculations of IR, Raman and UV-Vis spectra were computed to provide data guidelines for future experimental observations. Finally, the F-Mg and Mg-Mg chemical bonds of the FMgn clusters were analyzed, including the critical bonding points (BCPs) of Laplacian of electron density (Δρ), electron localization function (ELF) and interaction region indicator (IRI). The kind and strength of chemical bonds reveal the mechanism by which the F atom was rapidly stabilized by Mgn (n = 2-20) host clusters.

Borozenes: Benzene-Like Planar Aromatic Boron Clusters

ConspectusWith three valence electrons and four valence orbitals, boron (2s22p1) is an electron-deficient element, resulting in interesting chemical bonding and structures in both borane molecules and bulk boron materials. The electron deficiency leads to electron sharing and delocalization in borane compounds and bulk boron allotropes, characterized by polyhedral cages, in particular, the ubiquitous B12 icosahedral cage. During the past two decades, the structures and bonding of size-selected boron clusters have been elucidated via combined photoelectron spectroscopy and theoretical investigations. Unlike bulk boron materials, finite boron clusters have been found to possess 2D structures consisting of B3 triangles, dotted with tetragonal, pentagonal, or hexagonal holes. The discovery of the planar B36 cluster with a central hexagonal hole provided the first experimental evidence for the viability of 2D boron nanostructures (borophene), which have been synthesized on inert substrates. The B7-, B8-, and B9- clusters were among the first few boron clusters to be investigated by joint photoelectron spectroscopy and theoretical calculations, and they were all found to possess 2D structures with a central B atom inside a Bn ring. Recently, the B73- (C6v), B82- (D7h), and B9- (D8h) series of closed-shell species were shown to possess similar π bonding akin to that in the C5H5-, C6H6, and C7H7+ series, respectively, and the name "borozene" was coined to highlight their analogy to the classical aromatic hydrocarbon molecules.Among the borozenes, the D7h B82- species is unique for its high stability originating from both its double aromaticity and the fact that the B7 ring has the perfect size to host a central B atom. The B82- borozene has been realized experimentally in a variety of MB8 and M2B8 complexes. In particular, the B82- borozene has been observed to stabilize the rare valence-I oxidation state of lanthanides in LnB8- complexes, as well as a Cu2+ species in Cu2B8-. The B6 ring in B73- is too small to host a B atom, resulting in a slight out-of-plane distortion. Interestingly, the bowl-shaped B7 borozene is perfect for coordination to a metal atom, leading to the observation of a series of highly stable MB7 borozene complexes. On the other hand, the B8 ring is slightly too large to host the central B atom, such that a low-lying and low-symmetry isomer also exists for B9-. Even though most 2D boron clusters are aromatic, the B73-, B82-, and B9- borozenes are special because of their high symmetries and their analogy to the series of C5H5-, C6H6, and C7H7+ prototypical aromatic compounds. This Account discusses recent experimental and theoretical advances on the investigations of various borozene complexes. It is expected that many new borozene compounds can be designed and may be eventually synthesized.

Electronic Control of the Position of the Pb Atom on the Surface of B8 Borozene in the PbB8 Cluster

Spontaneous symmetry-breaking is common in chemical and physical systems. Here, we show that by adding an electron to the C7v PbB8 cluster, which consists of a planar B8 disk with the Pb atom situated along the C7 axis, the Pb atom spontaneously moves to the off-axis position in the PbB8- anion. Photoelectron spectroscopy of PbB8- reveals a broad ground-state transition and a large energy gap, suggesting a highly stable closed-shell PbB8 borozene complex and a significant geometry change upon electron detachment. Quantum chemistry calculations indicate that the lowest unoccupied molecular orbital of the C7v PbB8 cluster is a degenerate π orbital mainly consisting of the Pb 6px and 6py atomic orbitals. Occupation of one of the 6p orbitals spontaneously break the C7v symmetry in the anion due to the Jahn-Teller effect. The large amplitude of the position change of Pb in PbB8- relative to PbB8 is surprising owing to bonding interactions between the Pb 6p orbital with the π orbital of the B8 borozene.

Electronic structure, stability, and aromaticity of M2B6 (M = Mg, Ca, Sr, and Ba): an interplay between spin pairing and electron delocalization

It has been shown in previous studies that the Be₂B₆ complex exhibits a triplet ground state with double aromaticity. In this work, the stability, electronic structure, and aromaticity of the homologous series M₂B₆ (M = Mg, Ca, Sr and Ba) were examined and compared to those of Be₂B₆. At the CCSD(T)/def2-TZVP//B3LYP/def2-TZVP level of theory, the target molecules were found to be more stable in the singlet than in the triplet spin state. Magnetically induced current densities and multicentre delocalization index (MCI) were employed to assess the aromatic character of the studied complexes. Both employed methods agree that M₂B₆ (M = Mg, Ca, Sr and Ba) are π aromatic and σ nonaromatic in the singlet ground state, and double aromatic in the triplet state. It was demonstrated that the electron counting rules of aromaticity cannot be used to correctly predict the aromaticity and relative stability of the examined molecules in different spin states.

AuB8-: an Au-borozene complex

Photoelectron spectroscopy and quantum chemistry studies are used to investigate the structure and bonding of AuB₈^-. Global minimum sturctural searches show that AuB₈^- possesses a chair-like structure, which can be viewed as Au⁺ bonded to the edge of the doubly-aromatic B₈^2- borozene, Au⁺[η²-B₈^2-]. Chemical bonding analyses reveal that the AuB₈^- is a novel borozene complex with unique Au-borozene bonding.

Exhaustive exploration of MgBn (n = 10–20) clusters and their anions

An unexpected tubular-shaped MgB₁₈ cluster is identified for the first time in alkaline-earth metal-doped boron clusters.

Exploring the Structure, Energetic, and Magnetic Properties of Neutral Small Lithium Clusters Doped with Yttrium: Supermagnetic Atom Research

Density functional theory calculations based on magnetic and energetic stability criteria were performed to study a series of yttrium-doped lithium neutral clusters. A relativistic approximation was employed to properly describe the energy and multiplicity of the given clusters' fundamental states. The interaction of the 4d-Y atomic orbitals with the sp-Li states had an important role in the magnetic and energetic behavior of the selected systems. The spin density was concentrated over the yttrium atom regardless of the size of the cluster. Li7Y is a new stable superatom due to its enhanced magnetic properties.

Electronic Structure and Thermochemical Parameters of the Silicon-Doped Boron Clusters BnSi, with n = 8-14, and Their Anions

We performed a systematic investigation on silicon-doped boron clusters BnSi (n = 8-14) in both neutral and anionic states using quantum chemical methods. Thermochemical properties of the lowest-lying isomers of BnSi(0/-) clusters such as total atomization energies, heats of formation at 0 and 298 K, average binding energies, dissociation energies, etc. were evaluated by using the composite G4 method. The growth pattern for BnSi(0/-) with n = 8-14 is established as follows: (i) BnSi(0/-) clusters tend to be constructed by substituting B atom by Si-atom or adding one Si-impurity into the parent Bn clusters with n to be even number, and (ii) Si favors an external position of the Bn frameworks. Our theoretical results reveal that B8Si, B9Si(-), B10Si and B13Si(-) are systems with enhanced stability due to having high average binding energies, second-order difference in energies and dissociation energies. Especially, by analyzing the MOs, ELF, and ring current maps, the enhanced stability of B8Si can be rationalized in terms of a triple aromaticity.