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) \(\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{5}\left(\mathrm{NO}_{2}\right)\right] \mathrm{Cl}_{2}\) 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 \(\left[\mathrm{Pt}\left(\mathrm{NH}_{3}\right)_{4}\right]\left[\mathrm{CuCl}_{4}\right]\) 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

Before matching the pairs of isomers with their corresponding isomerism types, we need to understand what each type means. - **Linkage Isomers:** These are isomers where the ligands can coordinate to the central metal atom/ion in different ways. Example: The nitro group (NO2) which can bind via the nitrogen or the oxygen. - **Coordination Isomers:** These are isomers where there's an exchange of ligands between a cationic and an anionic complex. - **Ionisation Isomers:** These are isomers that produce different ions in solution, usually swapping positions between a counterion and a ligand.

Step 2: Analyzing Pair 1

For the pair \[\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{5}\left(\mathrm{NO}_{2}\right)\right]\mathrm{Cl}_{2}\text{ and }\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{5}(\mathrm{ONO})\right]\mathrm{Cl}_{2}\]Both complexes have the same formula but the nitro group is coordinated to cobalt differently, either through nitrogen (NO2) or oxygen (ONO). Thus, they are correctly described as **linkage isomers**.

Step 3: Analyzing Pair 2

The pair \[\left[\mathrm{Cu}\left(\mathrm{NH}_{3}\right)_{4}\right]\left[\mathrm{PtCl}_{4}\right]\text{ and }\left[\mathrm{Pt}\left(\mathrm{NH}_{3}\right)_{4}\right]\left[\mathrm{CuCl}_{4}\right]\]Involves swapping ammonia ligands from the Cu complex to Pt and vice versa. This is a classic example of **coordination isomers**, as there's redistribution of both cationic and anionic components.

Step 4: Analyzing Pair 3

For the pair \[\left[\mathrm{Pt}\left(\mathrm{NH}_{3}\right)_{4}\mathrm{Cl}_{2}\right]\mathrm{Br}_{2} \text{ and }\left[\mathrm{Pt}\left(\mathrm{NH}_{3}\right)_{4}\mathrm{Br}_{2}\right]\mathrm{Cl}_{2}\]These represent **ionisation isomers**, as they interchange halides between coordinated ligands and counterions, leading to different ions in a solution.

Step 5: Selecting the Correct Answer

Since all three pairs (Pair 1, Pair 2, and Pair 3) correctly match with their isomer types, the correct selection is option (d) 1, 2, and 3.

Key Concepts

Linkage Isomers

In coordination chemistry, linkage isomers are fascinating because they demonstrate how molecules can coordinate differently to a central metal atom. This type of isomerism occurs when a ligand has multiple potential binding sites, leading to the formation of distinct complexes.

Consider the nitro group (NO2), which can attach itself to a metal ion through either nitrogen or oxygen. When it coordinates via nitrogen, it is represented as -NO2, while coordination through oxygen is noted as -ONO. Even though the chemical formula remains the same, the arrangement of atoms differs, giving rise to different chemical properties.

To visualize, imagine the complex \[\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{5}\left(\mathrm{NO}_{2}\right)\right]\mathrm{Cl}_{2}\] and \[\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{5}(\mathrm{ONO})\right]\mathrm{Cl}_{2}\]. In the first complex, the nitro group is bonded through nitrogen. However, in the second complex, it binds through oxygen. This variation in bonding leads to different linkage isomers, which can also impact the behavior and reactivity of the compound.

Understanding linkage isomerism helps us comprehend how minor changes in molecular structure can significantly affect the properties of coordination compounds.

Coordination Isomers

Coordination isomers highlight the interchange of ligands between complexes containing both cationic and anionic metal centers. This form of isomerism is unique because it involves a rearrangement of actual molecular components between two different metal centers, rather than altering attachment points within a single complex.

Take, for example, the complexes: \[\left[\mathrm{Cu}\left(\mathrm{NH}_{3}\right)_{4}\right]\left[\mathrm{PtCl}_{4}\right]\] and \[\left[\mathrm{Pt}\left(\mathrm{NH}_{3}\right)_{4}\right]\left[\mathrm{CuCl}_{4}\right]\]. In the first formation, copper is associated with ammonia, while the platinum is bound to chloride ions. In the second, these roles are reversed, and the ammonia ligands have swapped with the chloride counterparts.

Such transformations not only illustrate coordination isomerism but also provide valuable insight into the flexibility of molecular architecture in coordination chemistry. Although the total number of atoms and types of often elements remain unchanged, the resulting complexes can display different properties or reactivities, which underscores the importance of coordination isomers in chemical complexity and applications.

Ionisation Isomers

Ionisation isomers represent a type of isomerism where the permutation of ligands and counterions within a compound produces distinct ions in solution. While the overall composition remains constant, the location of specific ions changes, affecting the compound's properties and behavior in solution.

For instance, consider the two following compounds: \[\left[\mathrm{Pt}\left(\mathrm{NH}_{3}\right)_{4}\mathrm{Cl}_{2}\right]\mathrm{Br}_{2}\] and \[\left[\mathrm{Pt}\left(\mathrm{NH}_{3}\right)_{4}\mathrm{Br}_{2}\right]\mathrm{Cl}_{2}\]. In the first isomer, chloride ions are coordinated, and Br2 acts as counterions, while in the latter, the positions are interchanged. As a result, different ions are released into the solution.

The importance of ionisation isomers lies in their impact on the ionic environment in solutions, which can influence everything from reactivity to solubility. By understanding and manipulating these ions, chemists can tailor the properties of substances for specific applications. Ionisation isomerism is a perfect example of the nuanced complexity that coordination chemistry provides, demonstrating how the subtle redistribution of ions can create profound changes in a compound's characteristics.