Induced currents and electron counting in aromatic boron wheels: B8(2-) and B9-)

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Materials Science

Background:

• Aromaticity is a fundamental concept in chemistry, typically associated with cyclic, planar molecules with delocalized pi electrons.
• The exploration of novel aromatic systems beyond traditional organic compounds is crucial for understanding electronic structure and bonding.
• Boron clusters offer unique electronic and structural possibilities due to boron's electronic configuration.

Purpose of the Study:

• To investigate the aromaticity of newly discovered atom-centered polygonal boron wheels, specifically B8(2-) and B9-.
• To determine if these boron systems exhibit both pi- and sigma-aromaticity.
• To elucidate the electronic origins of their potential aromatic character.

Main Methods:

• Ipsocentric mapping of induced current density.
• Analysis of frontier molecular orbitals (HOMO and LUMO).
• Quantum chemical calculations to predict electronic properties.

Main Results:

• B8(2-) and B9- exhibit ring currents characteristic of aromatic systems.
• A pi diatropic current is attributed to the pi HOMO electrons, and a sigma diatropic current to the sigma HOMO electrons.
• Both pi and sigma aromaticity are predicted for B8(2-) and B9- based on magnetic criteria and orbital nodal properties.

Conclusions:

• The studied boron clusters, B8(2-) and B9-, are predicted to be both pi- and sigma-aromatic.
• The aromaticity arises from the specific nodal properties of their frontier pi and sigma orbitals.
• These findings expand the scope of known aromatic systems and highlight the unique chemistry of boron clusters.