Problem 109 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following pairs of isomers and types of isomerism are correctly matched? (1) \(\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{3}\left(\mathrm{NO}_{2}\right)\right] \mathrm{Cl}_{2}\) and \(\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{5}(\mathrm{ONO})\right] \mathrm{Cl}_{2}\) Linkage isomers (2) \(\left[\mathrm{Cu}\left(\mathrm{NH}_{3}\right)_{4}\right]\left[\mathrm{PtCl}_{4}\right]\) and \(\left[\mathrm{Pt}\left(\mathrm{NH}_{3}\right)_{4}\right] \quad\left[\mathrm{CuCl}_{4}\right]\) Co-ordinationIsomers (3) \(\left[\mathrm{Pt}\left(\mathrm{NH}_{3}\right)_{4} \mathrm{Cl}_{2}\right] \mathrm{Br}_{2}\) and \(\left[\mathrm{Pt}\left(\mathrm{NH}_{3}\right)_{4} \quad \mathrm{Br}_{2}\right] \mathrm{Cl}_{2}\) Ionisation Isomers Select the correct answer using the codes given below: (a) 1 and 2 (b) 2 and 3 (c) 1 and 3 (d) 1,2 and 3

Step-by-Step Solution

Answer

The correct answer is (d) 1, 2, and 3.

Step 1: Understanding Isomer Types

We are given three different pairs of coordination compounds and asked to identify which pair correctly matches a type of isomerism. The types of isomerism discussed are linkage isomers, coordination isomers, and ionisation isomers.

Step 2: Analyzing Pair (1)

Pair (1) consists of two coordination compounds, \[ [\mathrm{Co(NH}_3)_3(\mathrm{NO}_2)] \mathrm{Cl}_2 \quad \text{and} \quad [\mathrm{Co(NH}_3)_5(\mathrm{ONO})] \mathrm{Cl}_2 \]. They represent linkage isomerism, as the ligand \( \mathrm{NO}_2^- \) coordinates to the metal ion in two different ways: through either nitrogen or oxygen atoms. Therefore, pair (1) is correctly matched as linkage isomers.

Step 3: Analyzing Pair (2)

Pair (2) consists of coordination compounds,\[ [\mathrm{Cu(NH}_3)_4][\mathrm{PtCl}_4] \quad \text{and} \quad [\mathrm{Pt(NH}_3)_4][\mathrm{CuCl}_4] \]. They are coordination isomers because the ligands have exchanged coordination centers from copper to platinum and vice versa. Therefore, pair (2) is correctly matched as co-ordination isomers.

Step 4: Analyzing Pair (3)

Pair (3) involves coordination compounds\[ [\mathrm{Pt(NH}_3)_4 \mathrm{Cl}_2] \mathrm{Br}_2 \quad \text{and} \quad [\mathrm{Pt(NH}_3)_4 \mathrm{Br}_2] \mathrm{Cl}_2 \]. They show ionisation isomerism as the anions \(\mathrm{Cl}^-\) and \(\mathrm{Br}^-\) are interchanging between the coordination sphere and the counter-ion position. Thus, pair (3) is correctly matched as ionisation isomers.

Step 5: Selecting the Correct Codes

All the pairs, (1), (2), and (3) are correctly matched with their corresponding type of isomerism. Consequently, the correct option is (d) 1, 2, and 3.

Key Concepts

Linkage Isomers

Linkage isomers occur when a coordination compound has a ligand that can bind to the central metal at two different points. A perfect example is when a ligand contains more than one potential donor atom. In the exercise, for Pair (1), the ligand is nitrite, which can attach to cobalt via oxygen or nitrogen.

Imagine you have a key that can fit into a lock in two ways, either using one side of the key or flipping it to use the other side. Similarly, linkage isomers utilize the same ligand, but coordinate through different atoms.

This type of isomerism is fascinating because it illustrates how slight changes in atomic connectivity drastically alter the properties of the compound. You'll often detect these isomers by differences in their chemical and physical properties such as color and reactivity.

Coordination Isomers

Coordination isomers represent a distinct type of isomerism found specifically in coordination compounds. When analyzing Pair (2) from the exercise, we see that ligands commute between different central metal atoms within separate coordination complexes. Here, ammonia ligands switch places between copper and platinum metals.

Think of coordination isomers like swapping dance partners at a ball—they require organizational balance. These exchanges in place do not occur in random transition, but maintain the overall charge and balance of the compound.

Coordination isomers can affect the chemical behavior significantly, often exhibiting unique physical and chemical properties not observed in their counterparts. Recognizing these isomers requires understanding that different metals will conductively exchange their coordinating spheres.

Ionisation Isomers

Ionisation isomers arise when there is an exchange between the ligand within the coordination sphere and the ions outside it. In Pair (3), the chloride and bromide ions swap positions, displaying this particular isomerism type.

Consider ionisation isomers like a game of musical chairs, where ions change places but maintain the total tune or composition. When the elements inside the coordination sphere and those acting as counter-ions switch, the resulting isomers may exhibit distinct properties such as different solubilities and conductivities.

These isomers are essential in coordination chemistry, showing how intricate the balance between the coordination sphere and the outer environment is. By understanding ionisation isomers, you'll gain an insight into the dynamic nature of chemical bonding and complex formation.