Planar or tetrahedral? A ternary 17-electron CBe₅H₄⁺ cluster with planar pentacoordinate carbon

Abstract

A 17-electron CBe₅H₄⁺ cluster features planar pentacoordinate carbon, owing to the 2π/6σ double aromaticity. The neutral CBe₅H₄ cluster has a tetrahedral configuration despite its 18-electron counting. The latter species is governed by σ conjugation.