A halogen bond route to shorten the ultrashort sextuple bonds in Cr2 and Mo2

Abstract

Sextuple bonded group 6 diatomics Cr₂ and Mo₂ possess ultrashort metal–metal bonds. Yet their bond dissociation energy is very low. The destabilising nature of σ-bonds is responsible for this. Selective extraction of these σ-electrons via a σ-hole on a halogen bond donor shortens and strengthens the metal–metal bond. This study constitutes a hitherto unexplored application of halogen bonding and an example for the true violation of bond order–bond strength relation.