Boron–boron quadruple bond in Li3B2− and Li4B2 clusters

Abstract

Homopolar quadruple bonding in first row p-block elements is expected due to the presence of four valence orbitals accessible for bonding. Although quadruple bonding in C₂ has been proposed, no such proposal exists for B₂. Here we report the unprecedented B–B quadruple bonding in Li₃B₂⁻ and Li₄B₂ clusters based on high level theoretical calculations. The quadruple bonding is omnipresent in the global minimum, its nearest energy isomer and the transition states connecting them. Various bonding analyses reveal the unprecedented nature of the BB quadruple bonding interaction.