Concentric dual π aromaticity in bowl-like B30 cluster: an all-boron analogue of corannulene

Abstract

A chemical bonding model is presented for the bowl-like C_5v B₃₀ global-minimum cluster with a central pentagonal hole. The B₃₀ cluster is composed of three concentric boron rings: first B₅, second B₁₀, and third B₁₅. The first and second B rings constitute an inner double-chain ribbon and support a delocalized π sextet. The second and third rings form an outer double-chain ribbon, where 14π delocalized electrons are situated. The unique π systems lead to concentric dual π aromaticity for B₃₀, a concept established from concerted computational data on the bases of canonical molecular orbital (CMO) analysis, adaptive natural density partitioning (AdNDP), nucleus-independent chemical shifts (NICS), and natural charge calculations. A proposal is put forward that the bowl-like B₃₀ cluster is an exact all-boron analogue of corannulene (C₂₀H₁₀), a fragment of C₆₀ fullerene. The bonding nature of corannulene is revisited and fully elucidated herein. A comparison of the bonding patterns in bowl-like C_5v B₃₀ cluster and two other structural isomers (C_s and C₁) unravels the mechanism as to why the defective hole prefers to be positioned at the center.