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[Fe(H\(_2\)O)\(_5\)(ONO)]Cl and [Fe(H\(_2\)O)\(_5\)(NO\(_2\))]Cl are the examples of
[Fe(H\(_2\)O)\(_5\)(ONO)]Cl and [Fe(H\(_2\)O)\(_5\)(NO\(_2\))]Cl are the examples of
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Common ambidentate ligands include NO\(_2^-\) (N or O), CN\(^-\) (C or N), and SCN\(^-\) (S or N).
Updated On: May 10, 2026
- Solvate isomerism
- Geometrical isomerism
- Linkage isomerism
- Ionisation isomerism
- Coordination isomerism
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The Correct Option is C
Solution and Explanation
Step 1: Understanding the Concept
The question asks to identify the type of isomerism exhibited by the two given iron complexes. Isomers are compounds with the same chemical formula but different arrangements of atoms. We need to analyze the difference between the two given formulas.
Step 2: Detailed Explanation
Let's define the different types of isomerism and see which one fits.
Ionisation Isomerism: Occurs when the counter-ion of a complex is also a potential ligand and can exchange places with a ligand in the coordination sphere. For example, \([\text{Co}(\text{NH}_3)_5\text{Br}]\text{SO}_4\) and \([\text{Co}(\text{NH}_3)_5\text{SO}_4]\text{Br}\).
Solvate (or Hydrate) Isomerism: A specific type of ionisation isomerism where the exchange involves solvent molecules (often water). For example, \([\text{Cr}(\text{H}_2\text{O})_6]\text{Cl}_3\) and \([\text{Cr}(\text{H}_2\text{O})_5\text{Cl}]\text{Cl}_2 \cdot \text{H}_2\text{O}\).
Linkage Isomerism: Occurs when a ligand can bond to the central metal atom through two or more different atoms. Such ligands are called ambidentate ligands.
Geometrical Isomerism: Occurs in heteroleptic complexes due to different possible geometric arrangements of the ligands (e.g., cis-trans).
Coordination Isomerism: Occurs in compounds containing both cationic and anionic complex ions, where ligands are exchanged between the two.
Step 3: Analyzing the Given Complexes
The two complexes are \([\text{Fe}(\text{H}_2\text{O})_5(\text{ONO})]\text{Cl}\) and \([\text{Fe}(\text{H}_2\text{O})_5(\text{NO}_2)]\text{Cl}\). The chemical formula is the same for both. The only difference lies within the coordination sphere. - In the first complex, the ligand is ONO⁻ (nitrito), where the nitrite group is bonded to the iron atom through an oxygen atom (Fe-O-N=O). - In the second complex, the ligand is NO₂⁻ (nitro), where the nitrite group is bonded to the iron atom through the nitrogen atom (Fe-NO₂). The nitrite ion (NO₂⁻) is an ambidentate ligand because it can coordinate through either the nitrogen atom or one of the oxygen atoms. Isomerism that arises due to the different attachment points of an ambidentate ligand is the definition of linkage isomerism.
Step 4: Final Answer and Note on Provided Key
Based on the definition of structural isomerism in coordination chemistry, the given pair of complexes is a classic example of Linkage Isomerism (C).
However, the provided answer key indicates Ionisation Isomerism (D). This is incorrect. Ionisation isomers would differ in the ions produced in solution; both of these complexes would produce a \([\text{Fe}(\text{H}_2\text{O})_5(\text{ligand})]^+\) cation and a Cl⁻ anion. There is no exchange of the counter-ion with a ligand. The provided answer key appears to be erroneous, as the example perfectly fits the definition of linkage isomerism. For the purpose of this solution, we acknowledge the given answer but highlight the correct chemical principle. The correct answer by definition is (C).
The question asks to identify the type of isomerism exhibited by the two given iron complexes. Isomers are compounds with the same chemical formula but different arrangements of atoms. We need to analyze the difference between the two given formulas.
Step 2: Detailed Explanation
Let's define the different types of isomerism and see which one fits.
Ionisation Isomerism: Occurs when the counter-ion of a complex is also a potential ligand and can exchange places with a ligand in the coordination sphere. For example, \([\text{Co}(\text{NH}_3)_5\text{Br}]\text{SO}_4\) and \([\text{Co}(\text{NH}_3)_5\text{SO}_4]\text{Br}\).
Solvate (or Hydrate) Isomerism: A specific type of ionisation isomerism where the exchange involves solvent molecules (often water). For example, \([\text{Cr}(\text{H}_2\text{O})_6]\text{Cl}_3\) and \([\text{Cr}(\text{H}_2\text{O})_5\text{Cl}]\text{Cl}_2 \cdot \text{H}_2\text{O}\).
Linkage Isomerism: Occurs when a ligand can bond to the central metal atom through two or more different atoms. Such ligands are called ambidentate ligands.
Geometrical Isomerism: Occurs in heteroleptic complexes due to different possible geometric arrangements of the ligands (e.g., cis-trans).
Coordination Isomerism: Occurs in compounds containing both cationic and anionic complex ions, where ligands are exchanged between the two.
Step 3: Analyzing the Given Complexes
The two complexes are \([\text{Fe}(\text{H}_2\text{O})_5(\text{ONO})]\text{Cl}\) and \([\text{Fe}(\text{H}_2\text{O})_5(\text{NO}_2)]\text{Cl}\). The chemical formula is the same for both. The only difference lies within the coordination sphere. - In the first complex, the ligand is ONO⁻ (nitrito), where the nitrite group is bonded to the iron atom through an oxygen atom (Fe-O-N=O). - In the second complex, the ligand is NO₂⁻ (nitro), where the nitrite group is bonded to the iron atom through the nitrogen atom (Fe-NO₂). The nitrite ion (NO₂⁻) is an ambidentate ligand because it can coordinate through either the nitrogen atom or one of the oxygen atoms. Isomerism that arises due to the different attachment points of an ambidentate ligand is the definition of linkage isomerism.
Step 4: Final Answer and Note on Provided Key
Based on the definition of structural isomerism in coordination chemistry, the given pair of complexes is a classic example of Linkage Isomerism (C).
However, the provided answer key indicates Ionisation Isomerism (D). This is incorrect. Ionisation isomers would differ in the ions produced in solution; both of these complexes would produce a \([\text{Fe}(\text{H}_2\text{O})_5(\text{ligand})]^+\) cation and a Cl⁻ anion. There is no exchange of the counter-ion with a ligand. The provided answer key appears to be erroneous, as the example perfectly fits the definition of linkage isomerism. For the purpose of this solution, we acknowledge the given answer but highlight the correct chemical principle. The correct answer by definition is (C).
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