Thermochemical properties, electronic structure and bonding of mixed lithium boron clusters (BnLi, n=1–8) and their anions

Dehydrogenation of diborane on small Nbn+ clusters

The reactivity of Nbn+ (1 ≤ n ≤ 21) clusters with B2H6 is studied by using a self-developed multiple-ion laminar flow tube reactor combined with a triple quadrupole mass spectrometer (MIFT-TQMS). The Nbn+ clusters were generated by a magnetron sputtering source and reacted with the B2H6 gas under fully thermalized conditions in the downstream flow tube where the reaction time was accurately controlled and adjustable. The complete and partial dehydrogenation products NbnB1-4+ and NbnB1-4H1,2,4+ were detected, indicative of the removal of H2 and likely BHx moieties. Interestingly, these NbnB1-4+ and NbnB1-4H1,2,4+ products are limited to 3 ≤ n ≤ 6, suggesting that the small Nbn+ clusters are relatively more reactive than the larger Nbn>6+ clusters under the same conditions. By varying the B2H6 gas concentrations and the reactant doses introduced into the flow tube, and by changing the reaction time, we performed a detailed analysis of the reaction dynamics in combination with the DFT-calculated thermodynamics. It is demonstrated that the lack of cooperative active sites on the Nb1+ cations accounts for the weakened dehydrogenation efficiency. Nb2+ forms partial dehydrogenation products at a faster rate. In contrast, the Nbn>6+ clusters are subject to more flexible vibrational relaxation which disperse the energy gain of B2H6-adsorption and thus are unable to overcome the energy barriers for subsequent hydrogen atom transfer and H2 release.

A DFT study to investigate the physical, electrical, optical properties and thermodynamic functions of boron nanoclusters (MxB2n0; x=1,2, n=3,4,5)

First Principle DFT calculations employing the B3LYP/LanL2DZ/SDD level of theory were used to analyze the various characteristics of boron nanoclusters (B6, B8, and B10). These pure structures were further doped with four transition metals (Ta, Ti, Tc, and V) to examine the enhancement of the pure structures' structural, electrical, and optical features. To study structural stability, we have estimated cohesion energy and imaginary frequencies. Cohesion energies were entirely negative, with a range of -3.37 eV to -8.07 eV, and most constructions had no imaginary frequencies, indicating their structural occurrences. The calculated adsorption energy suggests that the order of stability of the pristine boron nanoclusters is B10>B8>B6, and TcB10 and Tc2B10 are the more stable structures. Mulliken charge, DOS, HOMO-LUMO, and the HOMO-LUMO gap have all been examined in-depth to provide insight into electrical characteristics. UV-Vis and CD measurements show the doped boron nanoclusters have excellent optical properties. Aside from calculating thermodynamic functions, we have also calculated the global DFT parameters, which give us a deep quantum mechanical understanding of the optimized structure for further research and applications in the field of science and technology.

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.

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.

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.

LiB13: A New Member of Tetrahedral-Typed B13 Ligand Half-Surround Cluster

It will get entirely unusual derivatives with gratifying chemical bonding schemes for boron clusters by doping with lithium, the lightest alkalis. The geometric structures and electronic properties of the LiBn0/- (n = 10-20) clusters have been studied through Crystal structure AnaLYsis by Particle Swarm Optimization (CALYPSO) structural search approach along with the density functional theory (DFT) calculations. The low-lying candidates of LiBn0/- (n = 10-20) are reoptimized at the B3LYP functional in conjunction with 6-311 + G(d) basis set. Three forms of geometric configurations are identified for the ground-state structures of LiBn0/- clusters: half-sandwich-type, quasi-planar and drum-type structures. The photoelectron spectra (PES) of the LiBn- clusters have been calculated through time-dependent density functional theory (TD-DFT). A promising LiB13 with tetrahedral-typed B13 ligand half-surround cluster and robust stability is uncovered. The molecular orbital and adaptive natural density partitioning (AdNDP) analysis show that B-B bonds in the B13 moiety combined with the interaction between the B13 shell and Li atom stabilize the C2v LiB13 cluster. Our results advance the fundamental understanding about the alkali metal doped boron clusters.

The Studies on Structure and Stability of CaBn Clusters

Calcium-boron systems have excellent properties of hardness, strength, and chemical stability, and we studied a series of CaB_n clusters to investigate their structures and relative stability. The results showed the most stable structures of CaB_n clusters are not planar. The B atoms tend to get together and form the planar ring to stabilize the structure, and the Ca atoms are coordinated to the periphery of the formations. The average binding energy (E_b), fragmentation energy (E_F), second-order energy difference (Δ₂E), adiabatic detachment energy (ADE), and adiabatic electron affinity (AEA) of the CaB_n clusters were calculated to investigate the relative stability and the ability of removing or obtaining an electron. As shown by the results, E_F and Δ₂E values had obvious odd-even alteration as n increased, which indicated that the formations CaB₄, CaB₆, and CaB₈ were more stable. The ADE values for CaB_n clusters with even values of n were higher than those with odd values of n, which indicated CaB_n clusters with even values of n had difficultly removing an electron. The AEA values of CaB₃ and CaB₇ were larger than the others, which meant CaB₃ and CaB₇ easily obtained an electron. These results provide a useful reference for understanding the formation mechanism and stability of the alkaline earth metal boride as well as guidance for synthesizing the CaB_n clusters.

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.

Density functional theory study on structure and stability of BeBn+ clusters

RATIONALE

Boride compounds hold promise for broad applications in the field of optoelectronics due to their high-temperature resistant, corrosion resistant and antioxidant properties. In order to reveal the formation mechanism of alkali and alkaline earth metal doped boron clusters, theoretical studies of these systems are required.

METHODS

All the possible geometrical structures of BeB_n⁺ clusters (n = 1-8) were optimized at the B3LYP/6-311+G(d) level; the harmonic vibration frequencies were obtained to examine the true stability and give the zero-point vibration energy at that theoretical level. The single point energies of all the structures were computed at the CCSD(T)/aug-cc-pVDZ level. For the most stable structures, the average binding energy (E_b ), the fragmentation energy (E_F ) and second-order difference of total energy (Δ₂ E) were used to evaluate the relative stability of clusters.

RESULTS

Most of the BeB_n⁺ clusters are planar in structure; the B atoms tend to aggregate to form a boron ring, and the coordinating Be atoms are on the periphery of the clusters. The fragmentation energy and second-order difference of total energy show that there is an obvious odd-even alteration as n increases, and local-maxima when n is odd.

CONCLUSIONS

A systematic theoretical investigation on the geometries, stabilities and electronic properties of BeB_n⁺ clusters has been carried out where n = 1-8. The results provide a useful reference for understanding the formation mechanism and stability of these clusters, as well as guidance for finding larger size clusters.

Structure and stability of small lithium-chloride LinClm(0,1+) (n ≥ m, n = 1–6, m = 1–3) clusters

Detailed theoretical investigations along with the experimental observations of new small chlorine-doped lithium clusters are presented.

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.