Question

The type of isomerism present in nitropentammine chromium (III) chloride is:

• A. Optical
• B. Linkage
• C. Ionization
• D. Polymerization

Hint:

Linkage isomerism occurs in ligands like NO$_2^-$, SCN$^-$, and CN$^-$, where multiple donor atoms exist.

Answer 1

The Correct Option is B

Step 1: Understanding the Complex - The chemical formula of nitropentammine chromium (III) chloride is: \[ {[Cr(NH}_3{)}_5({NO}_2)]Cl_2 \] This complex contains the nitro ligand (NO$_2$), which can bind through either the nitrogen or oxygen. 
Step 2: Types of Isomerism Optical Isomerism: Seen in chiral molecules with non-superimposable mirror images. Not applicable here. 
Ionization Isomerism: When exchange of anions leads to different compounds in solution. Not applicable.
Polymerization Isomerism: Occurs when two complexes have the same empirical formula but different molecular formulas. Not applicable. 
Linkage Isomerism: Occurs when a ligand can bind through two different atoms. (Correct Answer) 
Step 3: Linkage Isomerism in This Complex
The NO$_2$ group can bind via: 
Nitro form (NO$_2$-N) 
Nitrito form (ONO) 
Final Answer: The correct isomerism is linkage isomerism due to NO$_2$ binding through either N or O.

Answer 2

Nitropentammine chromium (III) chloride exhibits linkage isomerism.

Linkage isomerism occurs when a ligand can coordinate to the central metal atom/ion through two or more different atoms, but with the same molecular formula.

In this complex, the nitro group (NO₂) is an ambidentate ligand, meaning it can bind through either the nitrogen atom or one of the oxygen atoms.

When NO₂ binds through nitrogen, the complex is called the nitro isomer, whereas when it binds through oxygen, it is called the nitrito isomer.

These two different bonding modes create distinct compounds with different properties, but the same overall formula.

Thus, nitropentammine chromium (III) chloride shows linkage isomerism, a special type of coordination isomerism based on ligand attachment points.