title: Particle on a boron disk: ring currents and disk aromaticity in B20(2-).
abstract: The B20(2-) cluster is predicted to exhibit a planar sheet-like structure with a circular circumference. Orbital plots and energy correlations demonstrate the close correspondence between the electronic structure of B20(2-) and the Bessel functions describing the waves of a quantum mechanical particle confined to a disk. The π-band of B20(2-), and its B19(-) congener, contains 12 π-electrons, forming a (1σ)(2)(1π)(4)(1δ)(4)(2σ)(2) configuration, which corresponds to a "disk aromaticity" electron count. The analogy not only applies to the π-band, but also extends to the 50 valence σ-electrons. The occupied σ-orbitals are assigned on the basis of radial and angular nodes of the scalar disk waves. The magnetic response of the cluster was examined by Nucleus Independent Chemical Shift (NICS) values and current density calculations based on the ipsocentric model. B20(2-) is found to exhibit a remarkable inner paratropic current in the σ-channel and an outer diatropic current in the π-channel. The orbital excitations responsible for the antiaromaticity in σ and the disk-aromaticity in π are identified.
authors.affiliation: Department of Chemistry, University of Leuven , B-3001 Leuven, Belgium.
authors.forename: Truong Ba
authors.initials: TB
authors.lastname: Tai
authors.forename: Remco W A
authors.initials: RW
authors.lastname: Havenith
authors.forename: Jos L
authors.initials: JL
authors.lastname: Teunissen
authors.forename: Ahmet R
authors.initials: AR
authors.lastname: Dok
authors.forename: Simon D
authors.initials: SD
authors.lastname: Hallaert
authors.forename: Minh Tho
authors.initials: MT
authors.lastname: Nguyen
authors.forename: Arnout
authors.initials: A
authors.lastname: Ceulemans