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

Question

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

Step-by-Step Solution

Answer

a-q, b-p, c-r, d-s

Step 1: Analyzing Na2[Pt(SCN)4]

The compound Na2[Pt(SCN)4] contains the thiocyanate ligand (SCN). This ligand can bind to the metal center (Pt) in different ways, either through the sulfur or the nitrogen, leading to different structural isomers. This type of isomerism is called Linkage isomerism.

Step 2: Analyzing [CrCl2(NH3)4]NO3

In this compound, the nitrate NO3 can dissociate in solution, indicating that it is an ionizable component. This results in the ability to create ions upon dissolution, a characteristic of Ionisation isomerism.

Step 3: Analyzing [Pt(NO2)(gly)(NH3)]

The presence of the NO2 group linked to the metal can lead to different spatial arrangements around the central metal, such as cis or trans formations. This results in different geometric configurations, characteristic of Geometrical isomerism.

Step 4: Analyzing K3[Fe(OH)2(C2O4)2]

This compound contains bidentate ligands (like oxalate C2O4) that can lead to non-superimposable mirror images of the molecule, characteristic of Optical isomerism.

Key Concepts

Linkage Isomerism

Linkage isomerism occurs when a ligand can attach to the central metal atom through different atoms. This means that the same ligand can provide distinct coordination by using an alternative donor atom. A classic example is the thiocyanate ion,

• represented as SCN
• can bind through the sulfur (S) or the nitrogen (N) atom, making two possible linkage isomers.

In the coordination compound Na₂[Pt(SCN)₄], the SCN ligand can attach to the platinum either via the sulfur atom (S) creating one isomer, or via the nitrogen atom (N), creating another.
This results in distinct compounds with potentially different chemical properties.

Coordination Isomerism

Coordination isomerism involves the exchange of ligands between coordination compounds in a similar complex. This subtle exchange changes the coordination sphere of the metals involved. Coordination isomers are unique because the placement of the ligands within the complexes differs, although the chemical composition remains the same.
For example,

• in the coordination compound [CrCl₂(NH₃)₄]NO₃, chloride and ammonia are directly bonded to chromium while nitrate is outside the coordination sphere.
• Swapping these or rearranging how exactly they fit might result in an isomer with different chemical and physical properties.

Coordination isomerism is significant in the study of coordination compounds as it influences reactivity and interaction with other substances.

Geometrical Isomerism

Geometrical isomerism arises due to different possible spatial arrangements around a central metal atom. This form of isomerism often appears in square planar and octahedral complexes where the position of ligands can change without altering the basic connectivity.
In the compound [Pt(NO₂)(gly)(NH₃)], the arrangement of ligands can form either cis or trans isomers.

• Cis isomers have ligands adjacent to each other.
• Trans isomers have them opposite each other in the arrangement around the metal center.

This isomerism significantly affects the physical and chemical properties of the compound, including solubility and reaction rates.

Optical Isomerism

Optical isomerism is characterized by the presence of chiral centers in a compound, leading to non-superimposable mirror images known as enantiomers. These isomers rotate plane-polarized light in opposite directions.
In the compound K₃[Fe(OH)₂(C₂O₄)₂], the presence of bidentate ligands like oxalate that can bind to the central atom in a particular spatial arrangement forms such chiral centers.

• These chiral structures exist as a pair of enantiomers.
• They exhibit unique behavior in optical activity.

Optical isomerism is a crucial concept in chemistry and particularly vital in the design of many pharmaceuticals, as enantiomers can have very different biological activities.