Question

The compound(s) that exhibit(s) geometrical isomerism is(are) (A) \(\left[\right.\) Pt \(\left.(e n) \mathrm{Cl}_{2}\right]\) (B) \(\left[\mathrm{Pt}(\mathrm{en})_{2} / \mathrm{Cl}_{2}\right.\) (C) \(\left.\mid \mathrm{Pt}(\mathrm{en})_{2} \mathrm{Cl}_{2}\right] \mathrm{Cl}_{2}\) (D) \(\left.\mid \mathrm{Pt}\left(\mathrm{NH}_{3}\right)_{2} \mathrm{Cl}_{2}\right]\)

Short answer

The compound that exhibits geometrical isomerism is (D) \(\left.\mid \mathrm{Pt}\left(\mathrm{NH}_{3}\right)_{2}\mathrm{Cl}_{2}\right]\).

Step-by-step solution

- Understand Geometrical Isomerism

Geometrical isomerism occurs in coordination compounds with a specific spatial arrangement of ligands that can lead to non-superimposable configurations. This typically happens in octahedral complexes with cis/trans isomers or in square planar complexes when ligands can occupy different positions.

- Analyze the Ligands in Option A

For the complex \(\left[\right.\) Pt \(\left.(en) \mathrm{Cl}_{2}\right]\), 'en' stands for ethylenediamine, which is a bidentate ligand. Since there are only two chloride ions as other ligands, the spatial arrangement is fixed, allowing no geometrical isomerism.

- Analyze the Ligands in Option B

For \(\left[\mathrm{Pt}(\mathrm{en})_{2} / \mathrm{Cl}_{2}\right.\), we have two molecules of ethylenediamine (en) coordinating with platinum, creating a square planar arrangement. Since 'en' is bidentate and two 'en' ligands occupy all coordination sites, there is no room for isomerism.

- Analyze the Ligands in Option C

For \(\left.\mid \mathrm{Pt}(\mathrm{en})_{2} \mathrm{Cl}_{2}\right]\mathrm{Cl}_{2}\), similar to option B, there are two molecules of 'en' bidentate ligands, leading to a square planar coordination environment. This arrangement does not allow for geometrical isomerism.

- Analyze the Ligands in Option D

The complex \(\left.\mid \mathrm{Pt}\left(\mathrm{NH}_{3}\right)_{2}\mathrm{Cl}_{2}\right]\) has a square planar geometry with the central platinum atom surrounded by two ammonia molecules and two chloride ions. This allows for two different spatial arrangements of the ligands: the cis form, where the like ligands are next to each other, and trans form, where the like ligands are opposite to each other. Therefore, option D exhibits geometrical isomerism.

- Determine the Correct Option(s)

Considering the analysis from previous steps, only the complex in option D exhibits geometrical isomerism due to the possible cis and trans arrangements of its ligands in a square planar configuration.

Key concepts

JEE Advanced Chemistry

Preparing for the JEE Advanced Chemistry often involves understanding complex topics such as coordination compounds and their isomeric behaviors. One such intriguing aspect is geometrical isomerism in coordination compounds. Geometrical isomerism, or cis-trans isomerism, occurs due to the different possible arrangements of ligands around a central metal ion.

For students tackling problems in this area, visuals can greatly aid in comprehending the spatial distribution of ligands. Consider using models or diagrams to illustrate the possible isomeric forms. Remember, a clear grasp of how ligands can be rearranged can be crucial for predicting and explaining the properties of coordination complexes. As in standard JEE Chemistry fashion, it's not just about knowing facts but understanding the underlying principles that govern them.

Coordination Complexes

Coordination complexes are a pivotal point of study in inorganic chemistry. These entities consist of a central metal atom or ion bonded to multiple ligands, which can be neutral molecules or ions.

Ligands: The Attachments

Ligands play a significant role in the geometry and isomerism of a complex. They can be monodentate, binding through a single site, or bidentate like ethylenediamine (en), which attaches through two points.

Isomerism Considerations

When a coordination compound has a flexible geometry or multiple binding sites, it can exhibit geometrical isomerism. For example, square planar complexes may showcase cis (adjacent similar ligands) and trans (opposite similar ligands) isomers, a concept that becomes particularly relevant while solving JEE Advanced Chemistry problems involving coordination complexes.

Square Planar Geometry

Square planar geometry is often encountered with d8 metal ions, such as nickel (II), palladium (II), platinum (II), and gold (III). In a square planar complex, the central metal ion is at the center of a square, with four ligands positioned at the corners.

Implications for Isomerism

This geometry is conducive to geometrical isomerism due to the various positions that the ligands can occupy around the central ion.

When teaching this concept, emphasize that while some square planar complexes might appear to be able to form geometrical isomers, only those with at least two different types of mono-dentate ligands, or with mono-dentate and bidentate ligands, truly showcase isomerism. It's about understanding the arrangement: square planar complexes with symmetrical ligand arrangements, such as those with only bidentate ligands, do not have the cis-trans distinction, thus they do not exhibit geometrical isomerism.