The structure and chemical bonding in inverse sandwich B 6 Ca 2 and B 8 Ca 2 clusters: conflicting aromaticity vs. double aromaticity

• Published in: Physical chemistry chemical physics : PCCP 2020-09, Vol.22 (36), p.20362-20367
• Main Authors: Wang, Ying-Jin, Guo, Min-Min, Wang, Gui-Lin, Miao, Chang-Qing, Zhang, Nan, Xue, Teng-Dan
• Format: Article
• Language: English
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/D0CP03703F

The typical electron-deficiency of the boron element renders fascinating architectures and chemical bonding to boron-based nanoclusters. We theoretically predict two di-Ca-doped boron clusters, B 6 Ca 2 ( D 2h , 1 A g ) and B 8 Ca 2 ( D 8h , 1 A 1g ), and both adopt interesting inverse sandwich geometries, showing an elongated D 2h B 6 or perfectly planar D 8h B 8 ring being sandwiched by two Ca atoms only, respectively. Natural atomic charge analyses indicate that the Ca atoms donate nearly all the 4s electrons to the B 6 (or B 8 ) ring, forming [Ca] 2+ [B 6 ] 4− [Ca] 2+ and [Ca] 2+ [B 8 ] 4− [Ca] 2+ charge transfer complexes. The interaction between the two Ca atoms and the boron rings is governed by robust electrostatics albeit by weaker B–Ca covalent interaction. Chemical bonding analyses show that B 6 Ca 2 has 4σ and 6π delocalized electrons on the elongated B 6 ring, leading to a conflicting aromatic system. B 8 Ca 2 , possessing 6σ and 6π delocalized electrons on the B 8 ring, is doubly aromatic. Additionally, the B 6 Ca 2 and B 8 Ca 2 clusters show noticeable structural and electronic transmutation relative to their equivalent electronic B 6 Be 2 and B 8 Mg 2 clusters, respectively. The intrinsic reasons behind the transmutations are elucidated via in-depth bonding analyses.