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

Recent joint experimental and theoretical investigations have shown that seashell-like C-2 B-28 is the smallest neutral borospherene reported to date, while seashell-like C-s B-29(-) (1(-)) as a minor isomer competes with its quasi-planar counterparts in B-29(-) cluster beams. Extensive global minimum searches and first-principles theory calculations performed in this work indicate that with two valence electrons detached from B-29(-), the B-29(+) monocation favors a seashell-like C-s B-29(+) (1(+)) much different from C-s B-29(-) (1(-)) in geometry which is overwhelmingly the global minimum of the system with three B-7 heptagonal holes in the front, on the back, and at the bottom, respectively, unveiling an interesting charge-induced structural transition from C-s B-29(-)(1(-)) to C-s B-29(+) (1(+)). Detailed bonding analyses show that with one less sigma bond than B-29(-) (1(-)), C-s B-29(+) (1(+)) also possesses nine delocalized pi-bonds over its s-skeleton on the cage surface with a sigma + pi double delocalization bonding pattern and follows the 2(n + 1)(2) electron counting rule for 3D spherical aromaticity (n = 2). B-29(+) (1(+)) is therefore the smallest borospherene monocation reported to date which is pi-isovalent with the smallest neutral borospherene C-2 B-28. The IR, Raman, and UV-vis spectra of B-29(+) (1(+)) are computationally simulated to facilitate its spectroscopic characterization.