Question

Match Column-I (Type of isomerism) with Column-II (Examples): \[ \begin{array}{ll} \textbf{Column-I} & \textbf{Column-II} \\ A.\ \text{Linkage isomerism} & 1.\ [Co(NH_3)_5SO_4]Br/[Co(NH_3)_5Br]SO_4 \\ B.\ \text{Ionisation isomerism} & 2.\ [Co(NH_3)_5(NO_2)]Cl_2/[Co(NH_3)_5(ONO)]Cl_2 \\ C.\ \text{Coordination isomerism} & 3.\ [Co(NH_3)_6][Cr(CN)_6]/[Cr(NH_3)_6][Co(CN)_6] \end{array} \]

• A. A-2, B-1, C-3
• B. A-1, B-2, C-3
• C. A-3, B-2, C-1
• D. A-2, B-3, C-1

Hint:

Remember these common examples: \[ \boxed{ \begin{aligned} NO_2^-,\;SCN^- &\rightarrow \text{Linkage isomerism}\\ \text{Counter ion exchange} &\rightarrow \text{Ionisation isomerism}\\ \text{Ligand exchange between complexes} &\rightarrow \text{Coordination isomerism} \end{aligned} } \] These examples are among the most frequently asked in Coordination Chemistry.

Answer 1

The Correct Option is A

Concept: Coordination compounds exhibit several types of structural isomerism. The important ones are:

• Linkage isomerism: Caused by ambidentate ligands such as \(NO_2^{-}\) and \(SCN^{-}\).

• Ionisation isomerism: Caused by exchange between a coordinated ion and a counter ion.

• Coordination isomerism: Occurs in compounds containing both cationic and anionic complex ions due to interchange of ligands.

Step 1: Identify the linkage isomer.
The ligand \(NO_2^{-}\) can coordinate through either nitrogen or oxygen. Thus, \[ [Co(NH_3)_5(NO_2)]Cl_2 \] and \[ [Co(NH_3)_5(ONO)]Cl_2 \] are linkage isomers. Hence, \[ \boxed{A\rightarrow2.} \]

Step 2: Identify the ionisation isomer.
The compounds \[ [Co(NH_3)_5SO_4]Br \] and \[ [Co(NH_3)_5Br]SO_4 \] differ by interchange of the coordinated ion and counter ion. Hence, \[ \boxed{B\rightarrow1.} \]

Step 3: Identify the coordination isomer.
The compounds \[ [Co(NH_3)_6][Cr(CN)_6] \] and \[ [Cr(NH_3)_6][Co(CN)_6] \] are formed by interchange of ligands between two complex ions. Hence, \[ \boxed{C\rightarrow3.} \] Thus, \[ \boxed{ A-2,\; B-1,\; C-3 } \] Therefore, \[ \boxed{\textbf{Option (A)}} \] is the correct answer.