Problem 172 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following pairs represents linkage isomers? (a) \(\left[\mathrm{Pd}\left(\mathrm{P} \mathrm{Ph}_{3}\right)_{2}(\mathrm{NCS})_{2}\right]\) and \(\left[\mathrm{Pd}\left(\mathrm{P} \mathrm{Ph}_{3}\right)_{2}(\mathrm{SCN})_{2}\right]\) (b) \(\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{5} \mathrm{NO}_{3}\right] \mathrm{SO}_{4}\) and \(\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{5} \mathrm{SO}_{4}\right] \mathrm{NO}_{3}\) (c) \(\left[\mathrm{Pt} \mathrm{Cl}_{2}\left(\mathrm{NH}_{3}\right)_{4}\right] \mathrm{Br}_{2}\) and (d) \(\left[\mathrm{Cu}\left(\mathrm{NH}_{3}\right)_{4}\right]\left[\mathrm{Pt} \mathrm{Cl}_{4}\right]\) and \(\left[\mathrm{Pt}\left(\mathrm{NH}_{3}\right)_{4}\right]\left[\mathrm{CuCl}_{4}\right]\)

Step-by-Step Solution

Answer

(a) represents linkage isomers.

Step 1: Understand Linkage Isomers

Linkage isomers occur when a ligand, capable of coordinating through different atoms, forms complexes that differ in the atom attached to the metal center. Typically, this involves ambidentate ligands.

Step 2: Analyze Option (a)

Examine the pair \[\left[\mathrm{Pd}\left(\mathrm{P}\mathrm{Ph}_{3}\right)_{2}(\mathrm{NCS})_{2}\right] \text{ and } \left[\mathrm{Pd}\left(\mathrm{P}\mathrm{Ph}_{3}\right)_{2}(\mathrm{SCN})_{2}\right]\]Here, the ligand \(\mathrm{NCS}^-\) can bind through nitrogen or sulfur, forming linkage isomers. In the first complex, binding is through nitrogen (\(\mathrm{NCS}\)), while in the second it is through sulfur (\(\mathrm{SCN}\)).

Step 3: Analyze Option (b)

Examine the pair \[\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{5} \mathrm{NO}_{3}\right]\mathrm{SO}_{4} \text{ and } \left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{5} \mathrm{SO}_{4}\right]\mathrm{NO}_{3}\]These are coordination isomers, where the counter ion and part of the coordination sphere differ, not linkage isomers.

Step 4: Analyze Option (c)

Examine the complex \[\left[\mathrm{Pt} \mathrm{Cl}_{2}\left(\mathrm{NH}_{3}\right)_{4}\right]\mathrm{Br}_{2}\]This is just a coordination complex with no ambiguity in linkage.

Step 5: Analyze Option (d)

Examine the pair:\[\left[\mathrm{Cu}\left(\mathrm{NH}_{3}\right)_{4}\right]\left[\mathrm{Pt} \mathrm{Cl}_{4}\right] \text{ and } \left[\mathrm{Pt}\left(\mathrm{NH}_{3}\right)_{4}\right]\left[\mathrm{CuCl}_{4}\right]\]These are ionization isomers and not linkage isomers, as different ions exchange positions.

Key Concepts

Coordination Chemistry

Coordination chemistry is a fascinating field in chemistry that focuses on the interactions between metal ions and surrounding molecules or ions. These surrounding entities are known as ligands. The central metal ion and its associated ligands form what is called a coordination complex. In these complexes, metal-ligand bonds form via coordinate covalent bonds, where ligands donate pairs of electrons to the typically electron-deficient central metal atom.

Coordination chemistry is crucial for understanding the behavior of complex compounds in various chemical reactions, as well as in biological systems. For instance:

• In biological systems, coordination complexes are found in molecules such as hemoglobin and chlorophyll.
• In industrial applications, they are used in catalysts that speed up chemical reactions.
• They also play a role in the development of new materials and medicines.

The study of coordination chemistry helps us understand fundamental processes that occur both in nature and in engineered systems.

Complex Compounds

Complex compounds, also known as coordination compounds, consist of a metal center bonded to one or more ligands. The metal can attract and hold these ligands through coordinate bonding. The nature of these complexes lies in their ability to exist in various forms due to different coordination possibilities.

Complex compounds can exhibit several isomeric forms, including:

• Stereo isomerism: Where ligands occupy different positions in space relative to one another within the complex.
• Linkage isomerism: Where the same ligand can attach to the metal center through different atoms. For example, thiocyanate can link through either sulfur (SCN) or nitrogen (NCS).
• Ionization isomerism: Involves the interchange of anionic ligands between the coordination sphere and the rest of the complex.

These various forms provide insight into the arrangement and electronic interactions within a molecule. Understanding complex compounds and their properties is vital in areas like drug design, catalysis, and material science, where specific isomers can have drastically different behaviors and uses.

Ambidentate Ligands

Ambidentate ligands are ligands capable of coordinating to a metal ion in more than one way because they have more than one potential donor site. For instance, an ambidentate ligand like thiocyanate ( SCN ) can bind through either its nitrogen atom or its sulfur atom to the metal center.

The presence of ambidentate ligands can lead to the formation of linkage isomers, where the difference in connectivity can affect the properties and reactivity of the complex.

• Linkage isomers result when the point of attachment of the ligand atom to the metal changes.
• These isomers have the same molecular formula but different structures and properties.
• The choice of attachment directly influences the chemical behavior of the resulting complex, including its color, stability, and reactivity.

Knowing how ambidentate ligands interact with metal centers is essential for predicting and controlling the characteristics of coordination complexes in both synthetic and natural systems.