Li Wei-Li, Pal Rhitankar, Piazza Zachary A, Zeng Xiao Cheng, Wang Lai-Sheng
Department of Chemistry, Brown University, Providence, Rhode Island 02912, USA.
Department of Chemistry, University of Nebraska-Lincoln, Lincoln, Nebraska 68588, USA.
J Chem Phys. 2015 May 28;142(20):204305. doi: 10.1063/1.4921732.
Photoelectron spectroscopy and ab initio calculations have been carried out to probe the structures and chemical bonding of the B27 (-) cluster. Comparison between the experimental spectrum and the theoretical results reveals a two-dimensional (2D) global minimum with a triangular lattice containing a tetragonal defect (I) and two low-lying 2D isomers (II and III), each with a hexagonal vacancy. All three 2D isomers have 16 peripheral boron atoms and 11 inner boron atoms. Isomer I is shown to be mainly responsible for the observed photoelectron spectrum with isomers II and III as minor contributors. Chemical bonding analyses of these three isomers show that they all feature 16 localized peripheral B-B σ-bonds. Additionally, isomer I possesses 16 delocalized σ bonds and nine delocalized π bonds, while isomers II and III each contain 17 delocalized σ bonds and eight delocalized π bonds. It is found that the hexagonal vacancy is associated generally with an increase of delocalized σ bonds at the expense of delocalized π bonds in 2D boron clusters. The hexagonal vacancy, characteristic of borophenes, is found to be a general structural feature for mid-sized boron clusters. The current study shows that B27 (-) is the first boron cluster, where a hexagonal vacancy appears among the low-lying isomers accessible experimentally.
已进行光电子能谱和从头算计算，以探究B27 (-) 团簇的结构和化学键。实验光谱与理论结果的比较揭示了一个二维 (2D) 全局最小值，其具有包含四方缺陷的三角形晶格 (I) 和两个低能二维异构体 (II和III)，每个异构体都有一个六边形空位。所有这三种二维异构体都有16个外围硼原子和11个内部硼原子。结果表明，异构体I是观察到的光电子能谱的主要贡献者，异构体II和III的贡献较小。对这三种异构体的化学键分析表明，它们都具有16个局域化的外围B-B σ键。此外，异构体I拥有16个离域σ键和9个离域π键，而异构体II和III各自包含17个离域σ键和8个离域π键。研究发现，六边形空位通常与二维硼团簇中离域σ键的增加相关，代价是离域π键的减少。发现硼烯特有的六边形空位是中等尺寸硼团簇的一个普遍结构特征。当前研究表明，B27 (-) 是第一个在实验可及的低能异构体中出现六边形空位的硼团簇。
