Question

Which of the following coordination compounds shows linkage isomerism?

• A. \( [Co(NH_3)_5Cl]Cl_2 \)
• B. \( [Co(NH_3)_5(NO_2)]Cl_2 \)
• C. \( [Fe(CN)_6]^{3-} \)
• D. \( [Cr(H_2O)_6]Cl_3 \)

Hint:

\textbf{Tip:} Look for ambidentate ligands like NO\(_2^-\), SCN\(^-\), CN\(^-\) that can attach via multiple atoms.

Answer 1

The Correct Option is B

Linkage isomerism occurs in coordination compounds when the ligands can bind to the central metal atom/ion through different atoms. This typically involves ligands that contain more than one potential donor atom but only one atom can bind at a time. In the given options, we need to identify which compound demonstrates linkage isomerism. 

• \([Co(NH_3)_5Cl]Cl_2\)

The chloride ion, Cl⁻, involved here does not show linkage isomerism as it can only bind through a single atom.

• \([Co(NH_3)_5(NO_2)]Cl_2\)

The nitrite ion (\(NO_2^-\)) can coordinate to the metal center through the nitrogen atom to form the nitro isomer or through an oxygen atom to form the nitrito isomer. This ability to bind in two ways results in linkage isomerism.

• \([Fe(CN)_6]^{3-}\)

The cyanide ion (CN⁻) typically bonds through the carbon atom and does not show linkage isomerism as it cannot bind through the nitrogen atom effectively.

• \([Cr(H_2O)_6]Cl_3\)

Water (H₂O) acts as a ligand using oxygen and does not display linkage isomerism as it has only one donor atom.

Therefore, the compound that exhibits linkage isomerism is \([Co(NH_3)_5(NO_2)]Cl_2\) as it contains the nitrite ligand (NO₂⁻) which can coordinate in different ways.

Answer 2

Linkage isomerism occurs in coordination compounds when a ligand can bond to the central atom through more than one atom, leading to different structural forms. In such scenarios, the ligand possesses two or more potential donor atoms. An example of such ligands is the nitro ligand, \( NO_2^- \), which can bind through either the nitrogen atom (as nitro) or the oxygen atom (as nitrito).

Let's evaluate the given options:

Compound	Ligand Possibility
\([Co(NH_3)_5Cl]Cl_2\)	Does not have a ligand capable of linkage isomerism. Chloride (\(Cl^-\)) can only bind through chlorine.
\([Co(NH_3)_5(NO_2)]Cl_2\)	The nitro ligand (\(NO_2^-\)) can exhibit linkage isomerism, binding through nitrogen or oxygen.
\([Fe(CN)_6]^{3-}\)	Does not exhibit linkage isomerism. Cyanide (\(CN^-\)) binds through carbon only.
\([Cr(H_2O)_6]Cl_3\)	Water (\(H_2O\)) binds through oxygen, no other possibilities.

Therefore, the coordination compound that shows linkage isomerism is \([Co(NH_3)_5(NO_2)]Cl_2\), due to the presence of the nitro ligand.