This paper describes the synthesis and characterization of a Cr(I) dimer with a very short Cr-Cr distance. Computational studies support fivefold bonding between the chromium atoms. This paper could be used to introduce metal-metal multiple bonds and discuss the molecular orbital interactions of homonuclear diatomics including d-orbitals. More generally, it is a nice example to stimulate the discussion of what constitutes a bond and the various interpretations of bond order. This version of this learning object is a modified and expanded version of Maggie Geselbracht's original LO. It was prepared colleaboratively at the 2017 VIPEr Literature Discussion workshop.
Identify shapes and orientation of d orbitals
Create Lewis structures describing ligand binding type from crystal structures.
Apply symmetry concepts to assign orbital symmetries and create molecular orbital diagrams
Develop and draw the MO diagram of d-orbital interactions and use it to interpret the bonding involved in metal-metal multiple bonds.
Evaluate the relationship between bond order and experimental metal-metal bond distance
Evaluate effects of ligand design on molecular stability
Apply character tables for associated molecular point groups
Rationalize MO interactions of ligands with metal centers in the presence of a metal-metal multiple bond.
Students are asked to read the paper and answer the discussion questions before coming to class. This could be used in an inorganic course after you have talked about MO theory of diatomics but fairly early in our discussion of transition metal chemistry. There is a Perspectives article in Science that goes along with this paper that gives the MOs more explicitly.