Chem. J. Chinese Universities ›› 2023, Vol. 44 ›› Issue (10): 20230281.doi: 10.7503/cjcu20230281

• Physical Chemistry • Previous Articles    

Theoretical Study of MB8C4(M=Ca, Sr, Ba) Molecular Wheels Clusters with Dodeca-coordination Number in Plane

FENG Linyan1, HU Xiaobo1, YAN Miao1, MIAO Changqing1, CHEN Rui1, GUO Jinchang2(), WANG Yingjin1()   

  1. 1.Department of Chemistry,Xinzhou Teachers University,Xinzhou 034000,China
    2.Nanocluster Laboratory,Institute of Molecular Science,Shanxi University,Taiyuan 030006,China
  • Received:2023-06-14 Online:2023-10-10 Published:2023-08-14
  • Contact: WANG Yingjin E-mail:guojc@sxu.edu.cn;yingjinwang@sxu.edu.cn
  • Supported by:
    the National Natural Science Foundation of China(22173053);the Natural Science Foundation of Shanxi Province, China(202203021222305);the Scientific and Technological Innovation Programs of Higher Education Institutions in Shanxi Province, China(2022L463);the Project of Xinzhou Teachers University, China(2021KY04)

Abstract:

Searching for the maximum coordination number in planar species has attracted considerable attention from scientists. Although transition metal-centered boron molecular wheel haven been reported previously, there are relatively few studies on molecular wheel structures doped with main group metals. In this work, the geometric structures, chemical bonding, and aromaticity are investigated systemically at the B3LYP/def2-TZVP level for MB8C4(M=Ca, Sr, Ba) clusters. The results show that the global minimum structure of CaB8C4 cluster adopts perfect planar molecular wheel structure. The centered calcium atom enclosed by a highly symmetric B8C4 ring possesses the coordinate number(CN) of 12. The molecular wheel SrB8C4 cluster has a C4v symmetry with the out-of-plane distortion of the Sr atom, which are close in energy with elongated boron-carbon ring at CCSD(T)/def2-TZVP level. The latter has the actual coordination number of 8. Using a Ba, a larger atomic radius, to replace Sr in SrB8C4 cluster, the molecular wheel structure becomes less stable than elongated boron-carbon ring at CCSD(T)/def2-TZVP level. The natural bond orbital(NBO) analyses show that these systems undergo a large amount of charge transfer from alkaline earth metals to boron-carbon motifs. The MB8C4(M=Ca, Sr, Ba) molecular wheel can be formally described as [M]2+[B8C42- complexes. Chemical bonding analysis indicates that the dodeca-coordinated molecular wheel structure possesses 10σ and 8π conflicting aromaticity, which represents a counterexample in planar hyper-coordinated species. Adaptive natural density partitioning(AdNDP) analysis reveals that the interaction between the central alkaline earth metal and peripheral B8C4 monocyclic ring is governed by electrostatics and weakly covalent interaction. The latter mainly originate from contributions involving the M nd atomic orbitals, implying that alkaline earth metals mimic the behavior of transition metals. In addition, both the ring currents induced by an external magnetic field and the electron localization functions analysis results confirm the bonding characteristics of molecular wheel structures. We also predicted the infrared spectra of molecular wheel and elongated boron-carbon ring isomers, which provide theoretical guidance for experimental characterization of these clusters in future.

Key words: Boron-based nanoclusters, Molecular wheel, Density functional theory, Chemical bonding, Aromaticity

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