Question

The isomerism exhibited by the octahedral complex $[\mathrm{Co(NH_3)_4Br_2}]Cl$ is:

• A. Geometrical
• B. Optical
• C. Linkage
• D. Coordination
• E. Ionisation

Hint:

In octahedral complexes, cis-trans isomerism is common when two identical ligands are adjacent or opposite to each other.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
We need to determine the type(s) of isomerism possible for the given octahedral complex, [Co(NH\(_3\))\(_4\)Br\(_2\)]Cl. Isomerism in coordination compounds occurs when two or more compounds have the same chemical formula but different arrangements of atoms.
Step 2: Detailed Explanation of Isomerism Types:
Let's analyze the possibility for each type of isomerism listed for the complex [Co(NH\(_3\))\(_4\)Br\(_2\)]\(^+\)Cl\(^-\).
(A) Geometrical Isomerism (cis-trans): This occurs when ligands can be arranged differently in space around the central metal ion. The complex has the general formula [MA\(_4\)B\(_2\)], where M is Co, A is NH\(_3\), and B is Br. In an octahedral geometry, this type of complex can exist as two geometrical isomers:
- {cis}-isomer: The two Br ligands are adjacent to each other (at a 90\(^\circ\) angle).
- {trans}-isomer: The two Br ligands are opposite to each other (at a 180\(^\circ\) angle).
Since both cis and trans isomers can be formed, the complex exhibits geometrical isomerism.
(B) Optical Isomerism: This occurs when a complex is chiral (non-superimposable on its mirror image). For an [MA\(_4\)B\(_2\)] complex, the {trans}-isomer has a plane of symmetry and is achiral. The {cis}-isomer also possesses a plane of symmetry (passing through the Co atom and bisecting the Br-Co-Br and one NH\(_3\)-Co-NH\(_3\) angle) and is therefore achiral. So, this complex does not exhibit optical isomerism.
(C) Linkage Isomerism: This requires an ambidentate ligand, a ligand that can bind to the metal through two different atoms (e.g., NO\(_2\)\(^-\), SCN\(^-\)). Neither NH\(_3\) nor Br\(^-\) is ambidentate. So, no linkage isomerism is possible.
(D) Coordination Isomerism: This requires the exchange of ligands between a cationic and an anionic complex ion. The given compound consists of a complex cation and a simple anion (Cl\(^-\)). So, no coordination isomerism is possible.
(E) Ionisation Isomerism: This occurs when a counter ion can itself act as a ligand and displace a ligand from the coordination sphere. Here, the counter ion is Cl\(^-\). It can exchange with a Br\(^-\) ligand inside the sphere to form the isomer [Co(NH\(_3\))\(_4\)BrCl]Br. Since this is possible, the complex also exhibits ionisation isomerism.
Step 3: Conclusion:
The complex [Co(NH\(_3\))\(_4\)Br\(_2\)]Cl can exhibit both Geometrical isomerism and Ionisation isomerism. Since both (A) and (E) are possible answers, the question is ambiguous. However, geometrical isomerism is a very direct and certain feature of the [MA\(_4\)B\(_2\)] coordination sphere itself. Often in such ambiguous cases, the question refers to the isomerism within the coordination sphere. Given that, Geometrical Isomerism is the most prominent type. The fact that the question was cancelled in the source paper confirms this ambiguity.
Step 4: Final Answer:
The complex can exhibit both Geometrical and Ionisation isomerism. Since the question likely intended to ask about the isomerism within the coordination sphere [Co(NH\(_3\))\(_4\)Br\(_2\)]\(^+\), Geometrical isomerism is the primary answer. The question is officially marked as cancelled due to having more than one correct option.