The Al≡Al triple bond in Al2X5+ and Al2X62+(X=Li, Na) clusters with multiple alkali metals coordination

The studies on AlAl triple bonds in multi-coordinated aluminum clusters are rarely reported. Here, we report a series of Al2X5+ and Al2X62+ (X = Li, Na) clusters with five or six alkali metals that act as electron-donating ligands. Numerous bond analysis strategies indicate that they all contain AlAl triple bonds with one σ bond and two degenerated π bonds in these clusters at their global energy minima (GEMs). The AlAl triple bond does not change obviously in the singlet lowest-lying isomers with an increase in the number of Li+ or Na+ ions. Furthermore, these data indicate that [AlAl]4− is the core to stabilize these clusters and their stability is hardly affected by the numbers and positions of Li+ or Na+.