A case of a strongly polarized beryllium-beryllium bond

Bonding between two metals has long been a centre of attraction; in particular, the nature of dative bonding has always attracted the attention of chemists. The debate between dative and shared-covalent bonding is still ongoing even a century after their proposal. Herein, based on quantum chemical calculations, we have proposed the existence of a strongly polarized Be-Be bond in the [FBe → NHBe]^- adduct (NHBe = N-heterocyclic beryllium). This adduct follows the minimum-energy heterolytic-bond-cleavage pathway, fulfilling the minimum requirement for a dative bond. Moreover, various bonding and electronic structure analyses point towards a dative bond between the two fragments. Conversely, energy decomposition analysis (EDA) points towards a shared-covalent bond, creating two opposing views of the bond. The present article does not attempt to distinguish the type of bonding as "dative" or "covalent", as these are not mutually exclusive categories, but rather to show the formation of a strongly polarized homonuclear Be-Be bond. Furthermore, the high bond dissociation energy and significant negative Gibbs free energy values clearly indicate that the adduct may be experimentally detected in a low-temperature matrix or in the gas phase.