Animated Solution for Chemistry - Coordination Compounds: Match List-I and List-II. $\begin{array}{ll}\text{List-I}& \text{List-II}\\ \text{A. }[Co(N{H}_3{)}_6][Cr(CN{)}_6]& \text{1. Linkage isomerism}\\ \text{B. }[Co(N{H}_3{)}_3(N{O}_2{)}_3]& \text{2. Solvate isomerism}\\ \text{C. }[Cr(H_{2}O{)}_6]C{l}_3& \text{3. Co-ordination isomerism}\\ \text{D. }cis-[CrC{l}_2(ox{)}_2{]}^{3-}& \text{4. Optical isomerism}\end{array}$ Choose the correct answer from the options given below.

Isomerism in coordination chemistry is like a molecular puzzle where the same set of atoms can arrange themselves in fascinatingly different ways. In this problem, we are tasked with matching four distinct coordination complexes with their corresponding types of isomerism. Let's break down each complex and uncover the hidden logic behind its structure.

The Ligand Swap

Let's look closely at the first complex: $[Co(N{H}_3{)}_6][Cr(CN{)}_6]$.

Notice something unique? Both the cation and the anion are complex ions! When both parts of a salt are complex entities, the ligands have the freedom to interchange between the two metal centers. For instance, the ammonia ligands surrounding the cobalt can swap places with the cyanide ligands surrounding the chromium.

This beautiful exchange of ligands between coordination spheres is the hallmark of Coordination Isomerism. Therefore, complex A perfectly matches with option 3.

The Ambidentate Connection

Moving to the second complex, we have $[Co(N{H}_3{)}_3(N{O}_2{)}_3]$.

Focus your attention on the $N{O}_2^{-}$ ligand. This is a classic example of an ambidentate ligand. It possesses two different donor atoms: nitrogen and oxygen. It can donate its lone pair either from the nitrogen atom (forming a nitro complex) or from the oxygen atom (forming a nitrito complex, often written as $ON{O}^{-}$).

Depending on which atom connects to the central metal, we get different structural linkages. Hence, this complex exhibits Linkage Isomerism. So, complex B matches with option 1.

The Water Dance

Next up is the chromium complex: $[Cr(H_{2}O{)}_6]C{l}_3$.

Here, water molecules play a dual role. They can act as ligands tightly bound inside the coordination sphere, or they can migrate outside the sphere to become water of crystallization, while a chloride ion moves inside to take its place.

This dynamic exchange of solvent molecules between the inner coordination sphere and the outer crystal lattice is known as Solvate Isomerism (or Hydrate Isomerism when the solvent is water). Thus, complex C matches with option 2.

The Mirror Image

Finally, we examine the $cis-[CrC{l}_2(ox{)}_2{]}^{3-}$ ion.

Because it is the cis form containing bidentate oxalate ($ox$) ligands, the molecule lacks any internal plane of symmetry. If you were to draw its mirror image, you would find that it is non-superimposable on the original molecule—much like your left and right hands.

This inherent chirality means the complex will rotate plane-polarized light, exhibiting Optical Isomerism. Therefore, complex D matches with option 4.

Putting all our deductions together, we get the following sequence: - A $\to$ 3 - B $\to$ 1 - C $\to$ 2 - D $\to$ 4

Looking at the given choices, this sequence perfectly aligns with option (a). A highly conceptual problem that beautifully tests your fundamental grasp of structural and stereoisomerism!