Which of the following complex shows linkage isomerism?

Question

Accepted Answer

Linkage isomerism occurs in coordination compounds when a ligand can bind to the central metal atom through different atoms. This type of isomerism is possible when a ligand has more than one potential donor atom, allowing it to attach to the metal center in different ways.

1. **Option 1: $[Co(NH_{3})_{5}(NO_{2})]Cl_{2}$**  
   This complex exhibits linkage isomerism because the nitrite ligand (NO₂⁻) can bind to the cobalt metal center through either the nitrogen atom or one of the oxygen atoms. When the ligand binds through the nitrogen atom, it forms a nitro complex, and when it binds through an oxygen atom, it forms a nitrito complex. This ability to bind through different atoms makes linkage isomerism possible in this complex.

2. **Option 2: $[Co(NH_{3})_{5}(H_{2}O)]Cl_{3}$**  
   This complex does not show linkage isomerism because the water molecule (H₂O) is a monodentate ligand that can only bind through its oxygen atom. There are no alternative atoms in the water molecule that can act as donor atoms to the metal center, so linkage isomerism is not possible.

3. **Option 3: $[Pt(NH_{3})_{2}Cl_{2}]$**  
   This complex does not exhibit linkage isomerism because the ligands present (ammonia and chloride) are monodentate and can only bind through a single atom. Ammonia binds through nitrogen, and chloride binds through chlorine. There are no alternative binding sites within these ligands to allow for linkage isomerism.

4. **Option 4: $[Cr(H_{2}O)_{6}]Cl_{3}$**  
   Similar to Option 2, this complex does not show linkage isomerism because all the ligands are water molecules, which can only bind through their oxygen atoms. There are no alternative donor atoms in the water molecules, so linkage isomerism is not possible.

In conclusion, Option 1 is the correct answer because it contains the nitrite ligand, which can bind to the metal center through different atoms, allowing for linkage isomerism. The other options do not have ligands capable of such isomerism.