Question

Which is the correct pair of chelating and ambidentate ligands?

• A. Chelating: en, Ambidentate: \(NO_{2}^{-}\)
• B. Chelating: \(NH_{3}\), Ambidentate: \(H_{2}O\)
• C. Chelating: \(Cl^{-}\), Ambidentate: en
• D. Chelating: \(NO_{2}^{-}\), Ambidentate: \(C_{2}O_{4}^{2-}\)

Hint:

Remember the common ligand types: \[ \boxed{ \begin{aligned} NH_3,\;H_2O,\;Cl^- &\rightarrow \text{Monodentate}\\ en,\;C_2O_4^{2-} &\rightarrow \text{Chelating (Bidentate)}\\ EDTA &\rightarrow \text{Hexadentate}\\ NO_2^-,\;SCN^- &\rightarrow \text{Ambidentate} \end{aligned} } \] Chelating ligands form ring structures with the central metal ion.

Answer 1

The Correct Option is A

Concept: Ligands are classified according to the number of donor atoms and the manner in which they coordinate with the central metal ion.

• Chelating ligands possess two or more donor atoms and form one or more rings (chelates) with the metal ion.

• Ambidentate ligands possess two different donor atoms but coordinate through only one donor atom at a time.
Examples: \[ \boxed{ \begin{aligned} \text{Chelating ligands} &: en,\;C_2O_4^{2-},\;EDTA\\ \text{Ambidentate ligands} &: NO_2^{-},\;SCN^{-},\;CN^{-} \end{aligned} } \]

Step 1: Identify the chelating ligand.
Ethylenediamine (en) contains two nitrogen donor atoms. It coordinates through both nitrogen atoms simultaneously and forms a five-membered chelate ring. Hence, \[ \boxed{en\text{ is a chelating (bidentate) ligand}.} \]

Step 2: Identify the ambidentate ligand.
The nitrite ion, \[ NO_2^{-}, \] can coordinate either through the nitrogen atom (nitro) or through the oxygen atom (nitrito). However, it uses only one donor atom at a time. Therefore, \[ \boxed{NO_2^{-}\text{ is an ambidentate ligand}.} \]

Step 3: Examine the remaining options.

• \(NH_3\) and \(H_2O\) are monodentate ligands.

• \(Cl^{-}\) is also monodentate.

• \(C_2O_4^{2-}\) (oxalate) is a chelating ligand, not an ambidentate ligand.
Thus, \[ \boxed{\textbf{Option (A)}} \] is the correct answer.