Competition between quasi-planar and cage-like structures in the B₂₉⁻cluster: photoelectron spectroscopy and ab initio calculations

Abstract

Size-selected boron clusters have been found to be predominantly planar or quasi-planar (2D) in the small size regime with the appearance of three-dimensional (3D) borospherene cages of larger sizes. A seashell-like B cluster was previously shown to be the smallest borospherene, which competes with a quasi-planar isomer for the global minimum. Here we report a study on the structures and bonding of the B and B clusters using photoelectron spectroscopy (PES) and first-principles calculations and demonstrate the continued competition between the 2D and borospherene structures. The PES spectrum of B displays a complex pattern with evidence of low-lying isomers. Global-minimum searches and extensive theoretical calculations revealed a complicated potential energy surface for B with five low-lying isomers, among which the lowest three were shown to contribute to the experimental spectrum. A 3D seashell-like C (2, A') isomer, featuring two heptagons on the waist and one octagon at the bottom, is the global minimum for B, followed by a 2D C (3, A) isomer with a hexagonal hole and a stingray-shaped 2D C (1, A') isomer with a pentagonal hole. However, by taking into account the entropic effects, the stingray-shaped isomer 1 was shown to be the lowest in energy at room temperature and was found to dominate the PES spectrum. Isomers 2 and 3, which have lower electron binding energies, were also found to be present in the experiment. Chemical bonding analyses showed that isomer 1 is an all-boron analogue of benzo[ghi]fluoranthene (CH), whereas the borospherene isomer 2 possesses 18π electrons, conforming to the 2(N + 1) electron counting rule for spherical aromaticity. For the B neutral cluster, the seashell-like borospherene isomer is the global minimum, significantly lower in energy than the stingray-shaped quasi-planar structure.

Structures, stabilities and spectral properties of metalloborospherenes MB0/−40 (M = Cu, Ag, and Au)

“…Soon aer, the all-boron fullerene B 39 À was also produced via laser vaporization. 24 The rst observation of borospherene has aroused interest in boron clusters and their derivatives such as the dynamic behavior of B 40 , 25 hydrogen storage capacity of Ti-decorated B 40 , 26 ), 27,28 experimental and theoretical studies of B n À (n ¼ 27-29), [29][30][31] structures and properties of borospherenes (B 42 + , B 0/À 44 , and B 46 ), [32][33][34][35] structures of boron clusters B n (n ¼ 30 to 51) and exohedral complexation in C 6 H 6 CrB 40 , 36,37 CO 2 capture, storage and separation by borospherene B 40 , 38 and spectral properties of borospherenes B 0/À 40 . 39,40 Since the discovery of fullerene C 60 , 1 researchers have reported the development of several fullerene derivatives based on the functionalization of the C 60 aiming to produce new properties or improve their existing properties.…”

Heteroborospherene clusters Nin ∈ B40 (n = 1–4) and heteroborophene monolayers Ni2 ∈ B14 with planar heptacoordinate transition-metal centers in η7-B7 heptagons

“…As the light neighbor of carbon, boron has a rich chemistry dominated with multicenter two-electron bonds ( mc-2e bonds) in both bulk allotropes and polyhedral molecules to compensate for its electron-deficiency 3 . Multicenter bonds also appear to be responsible for the planar or quasi-planar (2D) structures of an unprecedentedly wide range of boron clusters B n −/0 (n = 3−30, 35, 36) characterized in gas phase in the past decade, unveiling a flat world of boron analogous to polycyclic aromatic hydrocarbons 4–18 . The possibility of all-boron fullerenes was not considered until 2007 when the high-symmetry I h B 80 cage was constructed from C 60 by capping the twenty hexagons 19 .…”

Lanthanide metals in the boron cages: Computational prediction of M@Bn (M = Eu, Gd; n = 38, 40)

“…Besides the carbon fullerenes, the boron clusters of certain sizes can form cage‐like structures as well, as exemplified by the recent fascinating discovery of the first borofullerene, D 2 d ‐ (Figure ) . After B 40 , more borofullerenes B n in neutral or ionic forms were observed in experiments or predicted by theory . Inspired by the facile preparation of EMFs, various endohedral derivatives of small borofullerenes were intensively proposed by computations as well.…”