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 Linkage Isomerism

Linkage isomers occur when a ligand can bind to the central atom in two different ways. In Pair (1), the ligand NO2 can bind through the nitrogen atom (resulting in NO2) or through the oxygen atom (resulting in ONO). Therefore, Pair (1) represents linkage isomerism.

Step 2: Understanding Coordination Isomerism

Coordination isomers involve the interchange of ligands between a complex cation and a complex anion. In Pair (2), ammonia (NH3) and chloride (Cl) ligands are switched between the copper and platinum centers, creating coordination isomers. Thus, Pair (2) is correctly matched as coordination isomers.

Step 3: Understanding Ionization Isomerism

Ionization isomers differ in which of the two anions or groups are inside the coordination sphere and which are outside. In Pair (3), Pt complex alternates between being surrounded with Cl- or Br- as counter ions, indicating ionization isomerism. It's correctly named for ionization isomerism.

Step 4: Selecting the Correct Set

Analyze the pairs based on their correctly matched isomerism type. Pairs (1), (2), and (3) each correctly match a type of isomerism: linkage, coordination, and ionization, respectively. Therefore, the correct answer is option (d), 1, 2, and 3.

Key Concepts

Linkage Isomerism

Linkage Isomerism is a unique phenomenon observed in coordination compounds. This type of isomerism occurs when a single ligand can attach to a central metal atom through different atoms, resulting in distinct compounds.
For instance, ligands like nitrite ( NO_2^-) exhibit linkage isomerism. It can bind to a central atom using the nitrogen atom, forming one isomer, or using the oxygen atom, forming a different isomer.

• The ligand NO_2^-) can connect through nitrogen, resulting in NO_2-bound isomers.
• Alternatively, it can connect through oxygen, creating ONO-bound isomers.

This kind of isomerism has a significant impact on the properties of a compound, such as its color, reactivity, or even biological activity. Understanding linkage isomerism helps chemists predict and manipulate the behavior of complex compounds.

Coordination Isomerism

Coordination Isomerism arises in coordination compounds, which consist of a complex cation paired with a complex anion. It occurs when there is an interchange of ligands between the cation and anion. This rearrangement leads to different compounds with potentially varying properties.
Imagine having a coordination compound like [ Cu(NH_3)_4 ] [ PtCl_4 ]. If the ammonia ( NH_3 ) ligands and the chloride ( Cl^-) ligands switch places between the copper and platinum centers, the result is new coordination isomers.

• In one isomer, NH_3 is paired with copper while Cl^-) is with platinum.
• In the other isomer, the situation reverses, with NH_3 on platinum and Cl^-) on copper.

This type of isomerism is fascinating as it influences the coordination sphere's overall geometry and its resulting chemical and physical characteristics. It often needs to be closely studied in complexes used in areas like catalysis or drug design.

Ionization Isomerism

Ionization Isomerism involves isomers that differ in the ion released into the solution when the compound dissolves. In these cases, what's inside the coordination sphere and what's outside as counter-ions alternate. This type of isomerism can greatly affect the solubility and reactivity of the compounds in question.
Consider a coordination compound represented by [ Pt(NH_3)_4Cl_2] Br_2. Here, Br_2 is the counter-ion outside the coordination sphere. In its isomeric form [ Pt(NH_3)_4Br_2] Cl_2 , Cl_2 becomes the new counter-ion.

• In the original compound, Pt(NH_3)_4 connects to Cl with Br_2 outside.
• In the isomer, Pt(NH_3)_4 links with Br with Cl_2 outside.

Ionization isomerism is crucial for compounds used in biological contexts or material science, where the correct ionization state is necessary for optimal function or interaction. Understanding this form of isomerism is key to controlling and predicting how coordination compounds behave in different environments.