Stop rotating! One substitution halts the B19− motor

Abstract

The B₁₉⁻ anion and other boron species have been dubbed ‘Wankel motors’ for the almost barrierless rotation of inner and outer concentric rings relative to each other in these compounds. A single substitution in B₁₉⁻ is shown to shut down the well-established fluxionality in the anion. A carbon atom substituted in the structure to give a neutral CB₁₈ species is shown computationally to enforce bond localization.