Theoretical prediction of Be–Be multiple bonding in a hydride-stabilized Be2Li4H− cluster

Abstract

The formation of triple or higher-order bonds in s-block homonuclear diatomic compounds, such as Be₂, remains a significant challenge due to their intrinsic electronic configurations. To date, no structural models, whether theoretical or experimental, support the presence of Be–Be quadruple bonding, as inferred from both computational predictions and spectroscopic analyses. Herein, we report for the first time a theoretical prediction of a hydride-coordinated dimeric Be–Be compound, formulated as Be₂Li₄H⁻, featuring a pseudo-quadruple Be–Be bonding interaction, which consists of three distinct Be–Be bonds (σ + 2π) and an additional weak Be–Be interaction. The latter arises from a Be–Be σ* orbital that gains stabilization via hydride-induced polarization, with the occupancy contributing significantly from delocalized electrons within the Li₄ units. This prediction is based on the previously reported double-π bonding D_4h-Be₂Li₄ model, with the additional introduction of an electron pair along the Be–Be axis and thus creates the fourth Be–Be weak bonding interaction. This distinctive bonding mode not only furnishes theoretical evidence for the viability of high bond-order Be–Be multiple-bonding interactions but also elucidates the complex multi-bonding phenomenon of s-block homonuclear diatomic systems.