Formation of the quasi-planar B50 boron cluster: topological path from B10 and disk aromaticity

Abstract

The lowest-lying isomer of the B₅₀ boron cluster is confirmed to have a quasi-planar shape with two hexagonal holes. By applying a topological (leap-frog) dual operation followed by boron capping, we demonstrated that such a quasi-planar structure actually comes from the smallest elongated B₁₀²⁻, and its high thermodynamic stability is due to its inherent disk aromaticity arising from its 32 valent π electrons that fully occupy a disk configuration of [(1σ)²(1π)⁴(1δ)⁴(2σ)²(1φ)⁴(2π)⁴(1γ)⁴(2δ)⁴(1η)⁴]. The aromatic character of the quasi-planar B₅₀ is further supported by a strong diatropic magnetic current flow. The sudden appearance of a quasi-planar B₅₀ again points out that the growth pattern of pure boron clusters is still far from being completely understood.