Question
Tue December 20, 2011 By: Akankshya Sahu
 

low oxidation states are found when a complex compound has ligands capable of pi-acceptor character in addition to the sigma-bonding.Explain.

Expert Reply
Wed December 21, 2011

Pi-acceptor ligand is a ligand that donates a pair of electrons from a lone pair to the metal center but also has the ability to accept electron density from the metal d orbitals into either d orbitals or pi-antibonding orbitals. Low oxidation state complexes can be stabilized by using ligands such as cyanide and carbon monoxide because these ligands are pi-acceptor ligands and these ligands have the capability to donate a pair of electrons from a lone pair to the metal center but also has the ability to accept electron density from the metal d orbitals into either d orbitals or pi-antibonding orbitals. A ligand with ?-acceptor properties has unoccupied orbitals at energies well above the metal dxy, dxz, and dyz orbitals with which mixing occurs to form ? and ?* orbitals. In this case, the ?* orbitals are localized on the ligand (not the metal). The former nonbonding d orbitals now become ? orbitals and are shifted to lower energies, thus increasing ?o.

 

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