Problem 134 - A Complete Resource Book in Chemistry for JEE Main

Question

$$ \begin{aligned} &\text { Match the following }\\\ &20\\\ &\begin{array}{ll} \hline \text { Column-I } & \text { Column-II } \\ \hline \text { (a) } \mathrm{Na}_{2}\left[\mathrm{Pt}(\mathrm{SCN})_{4}\right] & \text { (p) Ionisation } \\ \text { (b) }\left[\mathrm{CrCl}_{2}\left(\mathrm{NH}_{3}\right)_{4}\right] \mathrm{NO}_{3} & \text { (q) Linkage isomerism } \\ \text { (c) }\left[\mathrm{Pt}\left(\mathrm{NO}_{2}\right)(\mathrm{gly})\right. & \text { (r) Geometrical } \\ \left.\left(\mathrm{NH}_{3}\right)\right] & \text { isomerism } \\ \text { (d) } \mathrm{K}_{3}\left[\mathrm{Fe}(\mathrm{OH})_{2}\left(\mathrm{C}_{2} \mathrm{O}_{4}\right)_{2}\right] & \text { (s) optical isomerism } \\ & \text { (t) hydrate isomerism } \\ \hline \end{array} \end{aligned} $$

Step-by-Step Solution

Answer

(a) linkage isomerism, (b) ionization isomerism, (c) geometrical isomerism, (d) optical isomerism.

Step 1: Analyze Compound (a)

Consider the compound \( \text{Na}_2[\text{Pt}(\text{SCN})_4] \). The ligand SCN can bind through sulfur or nitrogen, which could lead to linkage isomerism.

Step 2: Analyze Compound (b)

For \( [\text{CrCl}_2(\text{NH}_3)_4]\text{NO}_3 \), the complex can exist as ionization isomers, which is due to the ability of \( \text{NO}_3^- \) to exchange with chloride ions \( \text{Cl}^- \) from the coordination sphere.

Step 3: Analyze Compound (c)

The compound \( [\text{Pt}(\text{NO}_2)(\text{gly})(\text{NH}_3)] \) has the potential for geometrical isomerism due to different possible spatial arrangements of the ligands around the central metal atom.

Step 4: Analyze Compound (d)

K3[Fe(OH)2(C2O4)2] involves oxalate ligands, which can exhibit optical isomerism as they allow for non-superimposable mirror images.

Key Concepts

Linkage Isomerism

Linkage isomerism occurs when a ligand that can attach to the central metal atom in more than one way results in different isomers. This is a fascinating aspect of coordination chemistry where the same ligand can bond through different atoms, causing distinct physical and chemical properties.
For example, the thiocyanate ion \[\text{SCN}^- \] can bind through sulfur to form \[\text{M-SCN} \] or through nitrogen to form \[\text{M-NCS}. \] The ability of a ligand to bind in multiple ways leads to varied molecular structures, an insight that is both intriguing and critical for students of chemistry.
Interesting enough, linkage isomers can display unique behaviors in terms of color, solubility, and reactivity. This diversity in characteristics underscores the importance of linkage isomerism in the study of complex ions.

Ionization Isomerism

Ionization isomerism takes place when a compound can form different ions in solution by exchanging ligands within and outside of the coordination sphere. This phenomenon is essential for understanding the versatility of coordination compounds.
In the example of \[ [\text{CrCl}_2(\text{NH}_3)_4]\text{NO}_3, \] the \(\text{NO}_3^-\) ion can be swapped with other ions such as \(\text{Cl}^-\), leading to distinct isomers known as ionization isomers.
This isomerism is crucial as it affects the ionic entities a compound releases in a solvent, impacting the properties and applications of the compound in fields such as catalysis and materials science. The ability of compounds to exist in multiple ionization states is vital for applications in chemical analysis and separation techniques.

Geometrical Isomerism

Geometrical isomerism involves the spatial arrangement of ligands around a central metal atom. This type of isomerism results from different possible configurations of ligands, especially in square planar and octahedral complexes.
Take, for instance, the compound \[ [\text{Pt}(\text{NO}_2)(\text{gly})(\text{NH}_3)].\] This compound can assume distinct geometrical positions whereby ligands are positioned differently around the platinum center, resulting in different isomers.

• In a square planar complex, ligands can be cis (adjacent) or trans (opposite).
• In an octahedral complex, different configurations such as facial (fac) or meridional (mer) are possible.

These varying arrangements hold tremendous importance because they can substantially alter the reactivity, stability, and biological activity of the compound. Understanding geometrical isomerism helps students appreciate how subtle changes at the molecular level can lead to significant chemical differences.

Optical Isomerism

Optical isomerism occurs when molecules are non-superimposable on their mirror images, akin to left and right hands. This form of isomerism is especially prevalent in coordination complexes containing chiral centers.
Consider \[\text{K}_3[\text{Fe(OH)}_2(\text{C}_2\text{O}_4)_2].\] Here, bidentate ligands like oxalate can create a chiral environment, leading to optical isomers known as enantiomers.
These enantiomers have the same physical properties except for their behavior towards polarized light and interactions with other chiral entities.

• One enantiomer might rotate plane-polarized light to the right (dextrorotary).
• The other enantiomer might rotate it to the left (levorotary).

Optical isomerism has wide implications, particularly in pharmaceuticals, where different enantiomers of a drug can have vastly different biological effects. This isomerism provides insight into the chirality concept, crucial for understanding complex organic and inorganic structures.