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Issue 9, 2018
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Ternary CBe4Au4 cluster: a 16-electron system with quasi-planar tetracoordinate carbon

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Abstract

Planar hypercoordinate carbons as exotic chemical species are dominated by 18-electron counting. We report herein a 16-electron planar tetracoordinate carbon (ptC) cluster, CBe4Au4, which is quasi-planar to be exact, being composed of a C center, a square-planar Be4 ring, and four outer Au bridges. The quasi-ptC cluster is established as a global minimum via computer structural searches, located 14.6 kcal mol−1 below the nearest competitor at the CCSD(T) level. It shows thermodynamic and electronic robustness, with a low electron affinity (1.54 eV at B3LYP) and a large HOMO–LUMO gap (2.21 eV for excitation energy). Bonding analyses reveal 2π and 6σ double aromaticity, in addition to four three-center two-electron (3c-2e) Be–Au–Be σ bonds, confirming that 16-electron counting is perfect for the system. We believe that double (π and σ) aromaticity is a general concept that governs planar or quasi-planar carbons, which overrides the 18-electron rule. Competition between quasi-ptC and tetrahedral carbon (thC) isomers in the CBe4M4 (M = K, Au, H, Cl) series is also examined, which sheds crucial light on factors that govern the ptC clusters. The present findings offer opportunities for further planar and unconventional molecules.

Graphical abstract: Ternary CBe4Au4 cluster: a 16-electron system with quasi-planar tetracoordinate carbon

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Publication details

The article was received on 16 Dec 2017, accepted on 29 Jan 2018 and first published on 13 Feb 2018


Article type: Paper
DOI: 10.1039/C7CP08420J
Citation: Phys. Chem. Chem. Phys., 2018,20, 6299-6306
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    Ternary CBe4Au4 cluster: a 16-electron system with quasi-planar tetracoordinate carbon

    J. Guo, L. Feng and H. Zhai, Phys. Chem. Chem. Phys., 2018, 20, 6299
    DOI: 10.1039/C7CP08420J

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