Neither too Classic nor too Exotic: One-Electron Na⋅B Bond in NaBH₃⁻ Cluster

It is here reported that the NaBH₃⁻ cluster exhibits a Na⋅B one-electron bond, a well-established type of electron-deficient bonding in the literature. The topological analysis of the electron localization function, at the correlated level, reveals that Na⁻, when approaching the bonding distance, fairly distributes its valence electron pair between two lobes. One of these electrons is used to bond with BH₃, which participates through its boron empty p-orbital. Furthermore, the bonding situation of LiBH₃⁻, KBH₃⁻, MgBH₃, and CaBH₃ global minima structures are similar to that of NaBH₃⁻, extending the family of these new one-electron bond systems with biradicaloid character.