Draw the structures of optical isomers of: (i) [Cr(C2O4)3]3– (ii) [PtCl2(en)2]2+ (iii) [Cr(NH3)2Cl2(en)]+

Optical isomers, or enantiomers, are compounds that are non-superimposable mirror images of each other. This property is particularly important in coordination chemistry, where the spatial arrangement of ligands around a central metal ion can lead to distinct optical isomers. Let’s break down the structures of the given complexes to illustrate their optical isomers.

1. Coordination Complex: [Cr(C2O4)3]³⁻

This complex features a chromium ion coordinated by three oxalate ligands (C2O4²⁻). The oxalate ligand is bidentate, meaning it can attach to the metal at two points, forming a chelate.

Structural Analysis

In this case, the arrangement of the three oxalate ligands around the chromium ion leads to a chiral geometry. Each oxalate ligand can be oriented in such a way that the overall coordination sphere lacks a plane of symmetry, which is crucial for optical activity.

• Isomer 1: One arrangement could have the oxalate ligands positioned in a clockwise manner around the chromium ion.
• Isomer 2: The mirror image of that arrangement would be the counterclockwise configuration.

These two arrangements are non-superimposable mirror images, confirming that [Cr(C2O4)3]³⁻ exhibits optical isomerism.

2. Coordination Complex: [PtCl2(en)2]²⁺

In this complex, platinum is coordinated by two chloride ions and two ethylenediamine (en) ligands. Ethylenediamine is also a bidentate ligand, which contributes to the potential for optical isomerism.

Geometric Consideration

Since the platinum ion has a square planar geometry, the arrangement of the ligands is crucial. The two en ligands can orient themselves in such a way that they create two distinct optical isomers.

• Isomer A: Both en ligands could be adjacent to each other, with chlorides on opposite sides.
• Isomer B: The arrangement could also have the en ligands across from each other, leading to a different spatial configuration.

These configurations result in two non-superimposable mirror images, confirming that [PtCl2(en)2]²⁺ has optical isomers.

3. Coordination Complex: [Cr(NH3)2Cl2(en)]+

This complex consists of chromium coordinated by two ammonia ligands, two chloride ions, and one ethylenediamine ligand. The presence of both bidentate and monodentate ligands complicates the arrangement but also allows for the possibility of chirality.

Exploring the Arrangement

In this case, the geometry of the chromium complex is likely octahedral. The arrangement of the ligands can create distinct optical isomers based on the positioning of the bidentate en ligand relative to the monodentate ligands.

• Configuration 1: The bidentate en ligand can be placed in a way that it wraps around two adjacent positions, while the chlorides occupy the remaining positions.
• Configuration 2: The mirror image of this arrangement would have the en ligand wrapping around the opposite positions, resulting in a non-superimposable structure.

Thus, [Cr(NH3)2Cl2(en)]+ can also exhibit optical isomerism through its unique spatial configurations.

Final Thoughts

In summary, the complexes [Cr(C2O4)3]³⁻, [PtCl2(en)2]²⁺, and [Cr(NH3)2Cl2(en)]+ all demonstrate optical isomerism due to their specific ligand arrangements around the metal center. Each complex offers unique spatial orientations that lead to the formation of non-superimposable mirror images. Understanding these structures not only highlights the beauty of coordination chemistry but also emphasizes the significance of chirality in chemical compounds.