title: 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 B28-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 B29-and B29clusters using photoelectron spectroscopy (PES) and first-principles calculations and demonstrate the continued competition between the 2D and borospherene structures. The PES spectrum of B29-displays a complex pattern with evidence of low-lying isomers. Global-minimum searches and extensive theoretical calculations revealed a complicated potential energy surface for B29-with five low-lying isomers, among which the lowest three were shown to contribute to the experimental spectrum. A 3D seashell-like Cs(2,1A') isomer, featuring two heptagons on the waist and one octagon at the bottom, is the global minimum for B29-, followed by a 2D C1(3,1A) isomer with a hexagonal hole and a stingray-shaped 2D Cs(1,1A') 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 (C18H10), whereas the borospherene isomer 2 possesses 18π electrons, conforming to the 2(N + 1)2electron counting rule for spherical aromaticity. For the B29neutral cluster, the seashell-like borospherene isomer is the global minimum, significantly lower in energy than the stingray-shaped quasi-planar structure.
authors.affiliation: Nanocluster Laboratory, Institute of Molecular Science, Shanxi University, Taiyuan 030006, China. hj.zhai@sxu.edu.cn lisidian@sxu.edu.cn.
authors.forename: Hai-Ru
authors.initials: HR
authors.lastname: Li
authors.affiliation: Department of Chemistry, Brown University, Providence, Rhode Island 02912, USA. lai-sheng_wang@brown.edu.
authors.forename: Tian
authors.initials: T
authors.lastname: Jian
authors.affiliation: Department of Chemistry, Brown University, Providence, Rhode Island 02912, USA. lai-sheng_wang@brown.edu.
authors.forename: Wei-Li
authors.initials: WL
authors.lastname: Li
authors.affiliation: Institute of Materials Science, Xinzhou Teachers' University, Xinzhou 034000, China.
authors.forename: Chang-Qing
authors.initials: CQ
authors.lastname: Miao
authors.affiliation: Nanocluster Laboratory, Institute of Molecular Science, Shanxi University, Taiyuan 030006, China. hj.zhai@sxu.edu.cn lisidian@sxu.edu.cn.
authors.forename: Ying-Jin
authors.initials: YJ
authors.lastname: Wang
authors.affiliation: Nanocluster Laboratory, Institute of Molecular Science, Shanxi University, Taiyuan 030006, China. hj.zhai@sxu.edu.cn lisidian@sxu.edu.cn and Institute of Materials Science, Xinzhou Teachers' University, Xinzhou 034000, China.
authors.forename: Qiang
authors.initials: Q
authors.lastname: Chen
authors.affiliation: Nanocluster Laboratory, Institute of Molecular Science, Shanxi University, Taiyuan 030006, China. hj.zhai@sxu.edu.cn lisidian@sxu.edu.cn.
authors.forename: Xue-Mei
authors.initials: XM
authors.lastname: Luo
authors.affiliation: Nanocluster Laboratory, Institute of Molecular Science, Shanxi University, Taiyuan 030006, China. hj.zhai@sxu.edu.cn lisidian@sxu.edu.cn.
authors.forename: Kang
authors.initials: K
authors.lastname: Wang
authors.affiliation: Nanocluster Laboratory, Institute of Molecular Science, Shanxi University, Taiyuan 030006, China. hj.zhai@sxu.edu.cn lisidian@sxu.edu.cn and State Key Laboratory of Quantum Optics and Quantum Optics Devices, Shanxi University, Taiyuan 030006, China.
authors.forename: Hua-Jin
authors.initials: HJ
authors.lastname: Zhai
authors.affiliation: Nanocluster Laboratory, Institute of Molecular Science, Shanxi University, Taiyuan 030006, China. hj.zhai@sxu.edu.cn lisidian@sxu.edu.cn.
authors.forename: Si-Dian
authors.initials: SD
authors.lastname: Li
authors.affiliation: Department of Chemistry, Brown University, Providence, Rhode Island 02912, USA. lai-sheng_wang@brown.edu.
authors.forename: Lai-Sheng
authors.initials: LS
authors.lastname: Wang