B182−: a quasi-planar bowl member of the Wankel motor family

Abstract

A quasi-planar member of the so-called ‘Wankel motor’ family, B₁₈²⁻, is found. This boron cluster is an electronically stable dianion and a concentric doubly σ- and π-aromatic system. The inner B₆ unit in B₁₈²⁻ undergoes quasi-free rotation inside the perimeter of the B₁₂ ring. The absence of any localized σ-bond between the inner ring and the peripheral boron atoms makes the system fluxional.