EE triple bonds (E = Group 13) promoted by charge transfer from alkali metals

Abstract

We report herein evidence of EE triple bonds (E = Group 13) promoted by the perpendicularly surrounding M₄ (M = Li and Na) motifs. The global minimum of E₂M₄ (E = B, Al, and Ga) is a D_4h-symmetry structure where E–E is surrounded perpendicularly by square M₄ motifs, whereas the C_s-symmetry structure formed by E–E–M surrounded partially by M₃ motifs is the lowest-energy structure for E = In and Tl. Chemical bonding reveals that strong charge transfer from M₄ to E₂ dimer not only provides efficient electrons to form EE triple bonds, but also the resulting electrostatic interactions between M₄ and E₂ play a driving force to stabilize these intriguing triply bonded species.