Question

The complex cation which has two isomers is :

• A. \(\left[ Co \left( H _2 O \right)_6\right]^{3+}\)
• B. \(\left[ Co \left( NH _3\right)_5 Cl \right]^{+}\)
• C. \(\left[ Co \left( NH _3\right)_5 NO _2\right]^{2+}\)
• D. \(\left[ Co \left( NH _3\right)_5 Cl \right]^{2+}\)

Hint:

Consider the different types of isomerism in coordination compounds, such as linkage isomerism, ionization isomerism, geometrical isomerism, and optical isomerism.

Answer 1

The Correct Option is C

The question asks for the complex cation that has two isomers. To solve this, we need to understand which of the given complexes can exhibit isomerism. Let's consider the complexes one by one:

1. \([ Co (H _2 O )_6]^{3+}\): This complex is of the type \(M(L)_6\). Here, all ligands are the same, so it does not show isomerism.
2. \([ Co (NH _3)_5 Cl ]^{+}\) and \([ Co (NH _3)_5 Cl ]^{2+}\): Both of these complexes are of the type \(M(L)_5X\) where \(X\) is a mono-dentate ligand (chloride ion). These typically do not show isomerism because all \(\text{NH}_3\) ligands are identical and position interchange does not form a distinct isomer.
3. \([ Co (NH _3)_5 NO _2]^{2+}\): This complex can exhibit linkage isomerism. Nitrito (\(NO_2^-\)) can bind to the central metal atom in multiple ways, either through the nitrogen atom (nitro linkage) forming \([ Co (NH _3)_5 (NO_2)]^{2+}\) or through the oxygen atom (nitrito linkage) forming \([ Co (NH _3)_5 (ONO)]^{2+}\). This change in attachment gives rise to isomerism known as linkage isomerism.

Therefore, the correct answer is \([ Co (NH _3)_5 NO _2]^{2+}\) as it is capable of exhibiting linkage isomerism.