Wheel-like, elongated, circular, and linear geometries in boron-based CnB7-n (n=0-7) clusters: structural transitions and aromaticity

作者：Feng, Lin-Yan; Zhai, Hua-Jin^*

来源：Physical Chemistry Chemical Physics, 2017, 19(35): 24284-24293.

DOI：10.1039/c7cp04327a

• QUADRATIC CONFIGURATION-INTERACTION
• DENSITY-FUNCTIONAL THEORY
• DOUBLE-HEXAGONAL VACANCY
• PHOTOELECTRON-SPECTROSCOPY
• PLANAR TETRACOORDINATE
• THEORETICAL EVIDENCE
• ELECTRONIC-STRUCTURE
• CARBON
• ISOMERS
• DISTORTIONS

We report a quantum chemical study on the structural and bonding properties of a series of boron-carbon mixed clusters with seven atoms: CnB7-n (n = 0-7). Global-minimum structures were searched using the Coalescence Kick (CK) method, followed by B3LYP/6-311+ G(d) calculations for full optimizations and energetics. Top candidate structures were further benchmarked at the single-point CCSD(T) level. Structural transitions were revealed to occur successively between wheel-like, elongated, circular, and linear geometries upon the increase of C contents in the clusters. Chemical bonding was elucidated via canonical molecular orbital (CMO) analyses and adaptive natural density partitioning (AdNDP). The number of delocalized electrons (sigma plus pi) in the clusters was shown to vary by one at a time from 5 sigma to 7 sigma, as well as from 3 pi to 6 pi, which allows aromaticity, antiaromaticity, and conflicting aromaticity to be precisely tuned according to the (4n + 2) and 4n Huckel rules. Delocalized p and s bonds and their electron counting appear to dictate the cluster structures of the whole series. Aromaticity in the systems was independently confirmed using nucleusindependent chemical shifts (NICSs). The monocyclic B2C5 cluster was shown to possess the greatest NICS values, consistent with its 6 pi plus 6 sigma electron countings for double aromaticity. Our analyses also shed light on the reason why C in the filled-hexagonal B6C cluster occupies a peripheral site rather than the center and why C avoids hypercoordination in B-C binary clusters. A similar argument should be valid for other B-C clusters in prior reports, such as B6C2-, B7C-, and B8C.

• 出版日期2017-9-21
• 单位山西大学