Question

In \(\left[\mathrm{Cr}\left(\mathrm{C}_{2} \mathrm{O}_{4}\right)_{3}\right]^{3-}\), the isomerism shown is [2002] (a) optical (b) ionization (c) geometrical (d) ligand

Short answer

The isomerism shown is optical (a).

Step-by-step solution

Understand the Compound Structure

The complex ion \([\mathrm{Cr}(\mathrm{C}_{2}\mathrm{O}_{4})_{3}]^{3-}\) consists of one chromium ion bonded to three oxalate ions. Oxalate ions are bidentate ligands, which means they can form two bonds with the central metal ion.

Determine the Type of Isomerism

In coordination chemistry, common types of isomerism include optical, ionization, geometrical, and linkage isomerism. Optical isomerism occurs when molecules are non-superimposable on their mirror images. Ionization isomerism involves the exchange of ions within or outside the coordination sphere. Geometrical isomerism deals with different spatial arrangements of ligands around the metal center. Ligand isomerism involves different arrangements of ligands themselves.

Analyze Possible Isomerism in the Compound

The complex \([\mathrm{Cr}(\mathrm{C}_{2}\mathrm{O}_{4})_{3}]^{3-}\) can potentially exhibit optical isomerism. This is because the complex is composed of a central metal ion with three bidentate ligands forming a chiral configuration, allowing for the existence of non-superimposable mirror images.

Identify the Correct Type of Isomerism

Given that the complex is capable of forming non-superimposable mirror images due to its chiral nature, the type of isomerism shown by \([\mathrm{Cr}(\mathrm{C}_{2}\mathrm{O}_{4})_{3}]^{3-}\) is optical isomerism.

Key concepts

Coordination Chemistry

Coordination chemistry is a fascinating sub-discipline of chemistry that deals with the study of complexes formed between metal ions and ligands. A central metal ion gets surrounded by molecules or ions called ligands to form a coordination complex. The number of bonds between the central metal and the ligands defines the coordination number.
Coordination complexes are crucial in many fields such as biochemistry, material science, and catalysis. They can vary in both structure and function, leading to different properties and reactivities.

• Coordination Sphere: This consists of the central metal ion and the ligands directly bonded to it.
• Ligands: These are ions or molecules that can donate a pair of electrons to the metal ion, and they can range from simple ions like chloride to complex molecules.
• Complexing Agent: The agent, often a metal ion, that forms a bond with ligands.

Coordination chemistry also delves into the interesting phenomena of isomerism. This is where a single coordination complex can exist in different forms, which is common in biological systems. Understanding these concepts is critical, especially when looking into the properties and synthetic applications of these complexes.

Bidentate Ligands

Bidentate ligands are a type of ligand capable of forming two bonds with a single metal ion. This feature allows them to form more stable complexes due to the chelate effect. The word "bidentate" originates from the Latin words "bi," meaning two, and "dentate," meaning teeth, which aptly describes how these ligands anchor themselves to the metal ion.
A common example of a bidentate ligand is the oxalate ion ( C_2O_4^{2-} ). This ion utilizes two oxygen atoms to form bonds with the central metal, effectively gripping onto it.
Some important characteristics of bidentate ligands include:

• Stability: Bidentate ligands increase the stability of the coordination compound through a concept known as the "chelate effect." This occurs because forming rings with the metal center is entropically favorable.
• Complexity: These ligands can form more intricate and stable structures when compared to their monodentate counterparts.
• Examples: Aside from oxalate, another example is ethylenediamine, a common bidentate ligand in coordination chemistry.

The ability of bidentate ligands to form such stable complexes is important in many applications, including catalysis, drug delivery, and the design of new materials.

Chiral Configuration

A chiral configuration in coordination chemistry refers to arrangements where the complex cannot be superimposed on its mirror image. This is analogous to how your left hand is a non-superimposable mirror image of your right hand. In ( [Cr(C_2O_4)_3]^{3-} ), we see such a chiral configuration where the complex is optically active because of asymmetry created by the bidentate ligands.
In general, optical isomerism is observed in octahedral complexes with bidentate ligands, like the complex with oxalate ions mentioned here.
Important concepts related to chiral configuration in coordination complexes include:

• Optical Activity: The ability of chiral compounds to rotate plane-polarized light, which is a key identifier of optical isomerism.
• Enantiomers: These are pairs of molecules that are non-superimposable mirror images. In coordination complexes, this can refer to the different spatial arrangements possible.
• Application: Understanding chiral configurations is crucial in pharmaceuticals and materials science, since the arrangement of atoms can drastically affect a compound's function.

An in-depth understanding of chiral configurations enhances our ability to manipulate and employ coordination complexes effectively in various scientific and industrial applications.