Linear group 13 E[triple bond, length as m-dash]E triple bonds.

The unexpected linear group 13 E[triple bond, length as m-dash]E triple bonds were herein uncovered with the D3h-symmetry E2M5+ (M = Li, Na, and K) clusters, where the linear M-E[triple bond, length as m-dash]E-M form is perfectly surrounded by M3 motifs. The increasing nonbonded electron density of the heavier main-group elements is the key issue for the trans-bent geometry, and yet it is strongly suppressed in E2M5+, creating two degenerate π bonds and one multi-center σ bond.