Question

Define Ambidentate Ligand with one example.

Hint:

Ambidentate ligands have two possible donor atoms but coordinate through only one at a time. Double salts dissociate completely into their constituent ions in aqueous solution.

Answer 1

Concept:
Ligands are ions or molecules that donate lone pairs of electrons to a central metal atom or ion. Double salts are compounds that dissociate completely into their constituent ions when dissolved in water.

(i) Ambidentate Ligand

Step 1: Definition.
An ambidentate ligand is a ligand that possesses two different donor atoms and can coordinate to the metal ion through either of them, but only one donor atom at a time.

Step 2: Example.
Nitrite ion: \[ NO_2^- \] can coordinate through nitrogen: \[ M-NO_2 \] or through oxygen: \[ M-ONO \] Hence, nitrite ion is an ambidentate ligand. Other examples include: \[ SCN^- \] and \[ CN^- \]

(ii) Double Salt

Step 1: Definition.
A double salt is a crystalline compound formed by the combination of two or more simple salts in a definite proportion. When dissolved in water, it dissociates completely into all of its constituent ions.

Step 2: Example.
Mohr's salt: \[ FeSO_4\cdot(NH_4)_2SO_4\cdot6H_2O \] On dissolution: \[ FeSO_4\cdot(NH_4)_2SO_4\cdot6H_2O \rightarrow Fe^{2+}+2NH_4^++2SO_4^{2-}+6H_2O \] Thus it behaves as a mixture of the constituent salts in solution. Hence: An ambidentate ligand can coordinate through two different donor atoms. A double salt is formed by crystallisation of two simple salts in a fixed ratio and dissociates completely in water.