Among the following which are ambidentate ligands?
(i) `NO_2^(-)`
(ii) `NO_3^(-)`
(iii) `C_2O_4^(2-)`
(iv) `SCN^(-)`

Options

A. (i) and (iii)
B. (i) and (iv)
C. (ii) and (iii)
D. (ii) and (iv)

Answer

To determine which of the given ligands are ambidentate ligands, we need to analyze each ligand based on its ability to donate electrons from different atoms. Ambidentate ligands are those that can coordinate to a metal center through two different atoms.

Let's evaluate each ligand:

1. **NO2⁻ (Nitrite Ion)**:
- The nitrite ion can coordinate through either the nitrogen atom (N) or the oxygen atom (O).
- When it coordinates through nitrogen, it forms a nitro complex, and when it coordinates through oxygen, it forms a nitrito complex.
- Therefore, NO2⁻ is an ambidentate ligand.

2. **NO3⁻ (Nitrate Ion)**:
- The nitrate ion typically coordinates through the nitrogen atom (N) only. It does not have a significant ability to coordinate through oxygen in a way that would classify it as ambidentate.
- Therefore, NO3⁻ is not an ambidentate ligand.

3. **C2O4²⁻ (Oxalate Ion)**:
- The oxalate ion can coordinate through either of its two oxygen atoms.
- It can form complexes by donating electrons from either of the two oxygen atoms, making it an ambidentate ligand.
- Therefore, C2O4²⁻ is an ambidentate ligand.

4. **SCN⁻ (Thiocyanate Ion)**:
- The thiocyanate ion can coordinate through either the sulfur atom (S) or the nitrogen atom (N).
- When it coordinates through sulfur, it forms thiocyanato, and when it coordinates through nitrogen, it forms isothiocyanato.
- Therefore, SCN⁻ is an ambidentate ligand.

**Conclusion**:
The ambidentate ligands among the given options are:
- (i) NO2⁻
- (iv) SCN⁻

Thus, the answer is (i) and (iv).