A supported Cr-Cr sextuple bond in an all-metal cluster

Herein, we report a distinct Cr-Cr sextuple bond with an ultra-short length stabilized by equatorial alkali metals. Bonding analyses indicate that the two desired 4p-pi bonds failed to be formed but the bonding strength is enhanced due to the introduction of alkali metals, weakening the Cr-Cr 4s-4s effect. The Cr-Cr sextuple bond comprises five explicit 3d-3d overlaps and another delocalized σ bond. The introduction of alkali metals weakens the 4s-4s effect but strengthens its five 3d-3d overlaps between Cr-Cr atoms, eventually resulting in a stronger Cr-Cr sextuple bond with an ultra-short Cr-Cr distance in an all-metal cluster.