Ultra-Weak Metal-Metal Bonding: Is There a Beryllium-Beryllium Triple Bond?

Metal-metal triple bonds featuring s-block element have not been reported until now. Only Be-Be double bonds between have been predicted theoretically based on the intuitive electron donation from four s1 type electron-donating ligands. Herein, we theoretically predicted a novel species featuring a Be-Be triple bond in the Li6 Be2 molecule. The molecule was found to be thermodynamically stable. The presence of the triple bond was confirmed by adaptive natural density partitioning (AdNDP), electron localization function (ELF), and atoms in molecules (AIM) analyses. Moreover, the mechanical strength of the Be-Be triple bond was analyzed by using compliance matrix, pointing towards its ultra-weak nature.