Question

What is an ambidentate ligand? Give examples.

Answer 1

Ambidentate ligands arise linkage isomerism in coordination complexes. This can only be achieved when the group attaching itself to the central metal atom is the same but the attaching sites are different.

Complete answer:
First let us see what ligands are. When a molecule or ion is bonded to a metal by coordinate bonding, that molecule or ion is called ligand.
Ambidentate ligand is a type of ligand which can attach to the central metal atom through atoms of two different elements. More specifically ambidentate ligands have more than one donor atom but during coordinate bond formation only one of them attaches itself to the central metal atom.
For example we can take the example of $SC{N^ - }$ group. It can attach to the central metal atom let us say $M$ from two different sites. Either from S or from N. If the ion is linked from S, it would look like $M - SCN$ and if it is linked from N, it would look like $M - NCS$ .
In the same way $C{N^ - }$ can link itself to the central atom from C or N. If the ion is linked from C, it would look like $M - CN$ and if it is linked from N, it would look like $M - NC$ .
We can also look at the $N{O_2}$ group. It can attach to the central metal atom from two different sites. Either from N or from O. If the ion is linked from N, it would look like $M - N{O_2}$ and if it is linked from O, it would look like $M - ONO$ .

Note: The availability of a group to attach from two different sites also raises the need to change in naming convention. For example in $SC{N^ - }$ group, if S is the donor atom it would be called thiocyanate and if N is the donor atom it is called isothiocyanate.