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Issue 17, 2016
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Aromatic character of planar boron-based clusters revisited by ring current calculations

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Abstract

The planarity of small boron-based clusters is the result of an interplay between geometry, electron delocalization, covalent bonding and stability. These compounds contain two different bonding patterns involving both σ and π delocalized bonds, and up to now, their aromaticity has been assigned mainly using the classical (4N + 2) electron count for both types of electrons. In the present study, we reexplored the aromatic feature of different types of planar boron-based clusters making use of the ring current approach. B3+/−, B42−, B5+/−, B6, B7, B82−, B9, B102−, B11, B12, B13+, B142− and B162− are characterized by magnetic responses to be doubly σ and π aromatic species in which the π aromaticity can be predicted using the (4N + 2) electron count. The triply aromatic character of B12 and B13+ is confirmed. The π electrons of B182−, B19 and B202− obey the disk aromaticity rule with an electronic configuration of [1σ2442] rather than the (4N + 2) count. The double aromaticity feature is observed for boron hydride cycles including B@B5H5+, Li7B5H5 and M@BnHnq clusters from both the (4N + 2) rule and ring current maps. The double π and σ aromaticity in carbon-boron planar cycles B7C, B8C, B6C2, B9C, B8C2 and B7C3 is in conflict with the Hückel electron count. This is also the case for the ions B11C5+/− whose ring current indicators suggest that they belong to the class of double aromaticity, in which the π electrons obey the disk aromaticity characteristics. In many clusters, the classical electron count cannot be applied, and the magnetic responses of the electron density expressed in terms of the ring current provide us with a more consistent criterion for determining their aromatic character.

Graphical abstract: Aromatic character of planar boron-based clusters revisited by ring current calculations

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Publication details

The article was received on 30 Nov 2015, accepted on 24 Feb 2016 and first published on 25 Feb 2016


Article type: Paper
DOI: 10.1039/C5CP07391J
Author version available: Download Author version (PDF)
Citation: Phys. Chem. Chem. Phys., 2016,18, 11919-11931
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    Aromatic character of planar boron-based clusters revisited by ring current calculations

    H. T. Pham, K. Z. Lim, R. W. A. Havenith and M. T. Nguyen, Phys. Chem. Chem. Phys., 2016, 18, 11919
    DOI: 10.1039/C5CP07391J

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