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Metal-Metal Bonds
Chapter 15
Metal-Metal Bonds
• Single, double, triple, and quadruple bonds
are possible in transition metal complexes.
– Figure 15-7; [Re3Cl12]3- and [Re2Cl8]2– The metal-metal bond distance in the dimer is
224 pm. It was the first complex found to have
a quadruple bond.
Look at other complexes that have metal-metal
Possible Bonding Interaction
between Metal d Orbitals
• Discuss the possible bonding interactions between
the two metal atoms.
– d orbital interactions.
• The interaction between dx2-y2 and dxy orbitals is
weak. Why?
– This interactions produces the  bonding.
• Occupancy of the  molecular orbitals contributes
only a small amount to the overall bonding.
– Figure 15.9 in book.
• What about the spacing between  and *?
Possible Bonding Interaction in a
Complex Containing M-M Bonds
• In an actual complex (e.g. [Re2Cl8]2-) the ligands
interact with the metal orbitals.
• What is the symmetry of this molecule?
• With which orbital combination do the ligands
interact most strongly?
• LGO treatment (ligands pointing toward the metal
• Interaction occur with multiple orbital
combinations on the metal but the strongest is with
the  MO’s (bonding and antibonding)
– Let’s look at the IR’s.
Possible Bonding Interaction in a
Complex Containing M-M Bonds
Possible Bonding Interaction in a
Complex Containing M-M Bonds
• New molecular orbitals form when
including the ligand interactions.
– Simplistic picture showing interaction only
between the ligands and certain d orbital
combinations on the metal atoms.
• Why isn’t the complex staggered? What
will rotation do to the energy of the MO’s?
Possible Bonding Interaction in a
Complex Containing M-M Bonds
• Compounds of the staggered conformation.
– What is the symmetry of [Os2Cl8]2-?
– Why is it staggered and why does it possess a
lower bond order?
• Formal shortness ratio.
– Table