B31− and B32−: chiral quasi-planar boron clusters

Abstract

Chirality plays an important role in nature. Nanoclusters can also exhibit chiral properties. We report herein a joint experimental and theoretical investigation on the geometric and electronic structures of B₃₁⁻ and B₃₂⁻ clusters, using photoelectron spectroscopy in combination with first-principles calculations. Two degenerate quasi-planar chiral C₁ enantiomers (I and II, ¹A) with a central hexagonal vacancy are identified as the global minima of B₃₁⁻. For B₃₂⁻, two degenerate boat-like quasi-planar chiral C₂ structures (VI and VII, ²A) with a central hexagonal vacancy are also found as the global minima, with a low-lying chair-like C_i B₃₂⁻ (VIII, ²A_u) also present in the experiment as a minor isomer. The chiral conversions in quasi-planar B₃₁⁻ and B₃₂⁻ clusters are investigated and relatively low barriers are found due to the high flexibility of these monolayer clusters, which feature multiple delocalized σ and π bonds over buckled molecular surfaces.