Problem 25 - A Complete Resource Book in Chemistry for JEE Main

Question

An example of hexadentate ligand is (a) iminodiacetate ion (b) 2,2 'bipyridyl (c) dimethyl glyoxime (d) ethylene diamine tetraacetate ion

Step-by-Step Solution

Answer

(d) Ethylene diamine tetraacetate ion (EDTA) is the hexadentate ligand.

Step 1: Understanding Ligands

In chemistry, ligands are ions or molecules that bind to a central metal atom to form a coordination complex. They can have different numbers of donor atoms that bind to the metal. The term 'hexadentate' specifically refers to ligands that can form six bonds with the metal center.

Step 2: Analyzing Option (d) Ethylene Diamine Tetraacetate Ion

The ethylene diamine tetraacetate ion, often abbreviated as EDTA, is known to have six donor atoms: two nitrogen atoms and four oxygen atoms (from carboxyl groups). This allows EDTA to form six coordinate bonds with a metal ion, making it a hexadentate ligand.

Step 3: Reviewing Other Options

For completeness, analyze the other options: - Iminodiacetate ion has three donor sites and is tridentate. - 2,2'-bipyridyl is a bidentate ligand with two donor nitrogen atoms. - Dimethyl glyoxime is a bidentate ligand with two donor atoms.

Step 4: Conclusion

Based on the analysis, ethylene diamine tetraacetate ion (EDTA) is the only hexadentate ligand among the given options. It effectively employs its six donor sites to bind to metal ions.

Key Concepts

Coordination Complex

A coordination complex is a fascinating chemical structure composed of a central metal atom or ion surrounded by molecules or ions known as ligands. These ligands form coordinate bonds with the central metal, which means they donate electron pairs to the metal.

The study of coordination complexes is crucial in understanding various biological and industrial processes. They are involved in

• Catalysis
• Biological functions (such as oxygen transport in hemoglobin)
• Material science applications

Some important terminology associated with coordination complexes includes:

• Coordination Sphere: Includes the central metal and its directly attached ligands
• Coordination Number: Refers to the number of ligand donor atoms bonded to the metal
• Ligand: A molecule or ion that donates a pair of electrons to the metal

Coordination complexes exhibit diverse geometries, such as octahedral, tetrahedral, and square planar, depending on the number and arrangement of ligands around the metal center.

Ethylene Diamine Tetraacetate (EDTA)

Ethylene diamine tetraacetate (EDTA) is a remarkable ligand known for its ability to form stable chelation complexes with metal ions. It is a hexadentate ligand, meaning it can attach to a metal ion via six donor atoms. In EDTA, there are two nitrogen atoms and four oxygen atoms from carboxyl groups, providing multiple points of attachment to a metal center.

EDTA is widely utilized in:

• Water softening
• Detoxification of heavy metals
• Medicine, particularly in chelation therapy
• Analytical chemistry for titrations involving metals

Its ability to effectively "wrap around" a metal ion not only stabilizes the metal but also prevents it from undergoing unwanted reactions. This complexation ability allows EDTA to sequester metal ions, making it incredibly useful in various industrial and environmental applications.

Chelation

Chelation is a process that involves the formation of multiple bonds between a single central metal ion and a large organic ligand. This large organic ligand is often a multidentate ligand, providing several points of contact to bind with the metal ion. Chelation is vital because it can stabilize metal ions and regulate their reactivity.

In real-world applications, chelation helps:

• Enhance nutrient absorption in fertilizers
• Treat heavy metal poisoning in the human body
• Control metal-catalyzed reactions in industrial processes

When EDTA acts as a chelating agent, it wraps around a metal ion with its multiple binding sites, forming a complex that is less likely to dissociate. This intricate process of chelation is fundamental to many chemical processes and applications. It not only stabilizes the reactive metal ions but also fulfills roles in areas such as medicine, agriculture, and environmental science.