Charge-induced structural transition between seashell-like B29− and B29+ in 18 π-electron configurations

Abstract

Recent joint experimental and theoretical investigations have shown that seashell-like C₂ B₂₈ is the smallest neutral borospherene reported to date, while seashell-like C_s B₂₉⁻ (1⁻) as a minor isomer competes with its quasi-planar counterparts in B₂₉⁻ cluster beams. Extensive global minimum searches and first-principles theory calculations performed in this work indicate that with two valence electrons detached from B₂₉⁻, the B₂₉⁺ monocation favors a seashell-like C_s B₂₉⁺ (1⁺) much different from C_s B₂₉⁻ (1⁻) in geometry which is overwhelmingly the global minimum of the system with three B₇ heptagonal holes in the front, on the back, and at the bottom, respectively, unveiling an interesting charge-induced structural transition from C_s B₂₉⁻ (1⁻) to C_s B₂₉⁺ (1⁺). Detailed bonding analyses show that with one less σ bond than B₂₉⁻ (1⁻), C_s B₂₉⁺ (1⁺) also possesses nine delocalized π-bonds over its σ-skeleton on the cage surface with a σ + π double delocalization bonding pattern and follows the 2(n + 1)² electron counting rule for 3D spherical aromaticity (n = 2). B₂₉⁺ (1⁺) is therefore the smallest borospherene monocation reported to date which is π-isovalent with the smallest neutral borospherene C₂ B₂₈. The IR, Raman, and UV-vis spectra of B₂₉⁺ (1⁺) are computationally simulated to facilitate its spectroscopic characterization.