Question

State a reason why $CO$ is stronger complexing reagent than $N{H_3}$?

Answer 1

As we know that a complexing reagent is the one which possesses the tendency to form a complex compound with another material present in a solution. And we also know that metal and carbon bonds possess sigma and pi characters both and ammonia forms complexes with metal ions.

Complete step by step solution:
- We already know that a complexing reagent forms a complex compound with other substances present in the solution.
- Now we know that $CO$ possess the empty pi-orbitals which basically overlaps with the filled d-orbitals of the transition metals and carbonyl complexes also possess the tendency of back bonding between metal and carbon bond where sigma bonds can be used as donors and pi-bonds can be used as acceptors and therefore electrons can be donated from the filled d-orbital of metals to the pi- molecular orbitals of carbonyls. So when metal binds to this ligand it creates a synergic effect that helps strengthen the bond between carbonyl ligand and the metal.
- Whereas in ammonia we know that it has a lone pair of electrons which it can donate to form complexes but it has a disadvantage as compared to carbonyl ligand that it can only form sigma bonds and does not form pi-bonds with metals.
- Therefore, from the above explanation we can say that carbonyl is a better and stronger complexing reagent as compared to ammonia.

Note: Always remember that carbonyl compound along with its complex forming ability it is always considered a better ligand due to the tendency of formation of back bonding between carbonyl and the metal it reacts with.