Experimental and Theoretical Evidence of an Axially Chiral Borospherene

Chirality plays an important role in chemistry, biology, and materials science. The recent discovery of the B40 –/0 borospherenes marks the onset of a class of boron-based nanostructures. Here we report the observation of axially chiral borospherene in the B39 – nanocluster on the bases of photoelectron spectroscopy, global minimum searches, and electronic structure calculations. Extensive structural searches in combination with density functional and CCSD(T) calculations show that B39 – has a C 3 cage global minimum with a close-lying C 2 cage isomer. Both the C 3 and C 2 B39 – cages are chiral with degenerate enantiomers. The C 3 global minimum consists of three hexagons and three heptagons around the vertical C 3 axis. The C 2 isomer is built on two hexagons on the top and at the bottom of the cage with four heptagons around the waist. Both the C 3 and C 2 axially chiral isomers of B39 – are present in the experiment and contribute to the observed photoelectron spectrum. The chiral borospherenes also exhibit three-dimensional aromaticity, featuring σ and π double delocalization for all valence electrons. Molecular dynamics simulations reveal that these chiral B39 – cages are structurally fluxional above room temperature, compared to the highly robust D 2d B40 borospherene. The current findings add chiral members to the borospherene family and indicate the structural diversity of boron-based nanomaterials.