Problem 33 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

The total number of coordination sites in ethylenediaminetetraacetate \(\left(\mathrm{EDTA}^{4-}\right)\) is

Step-by-Step Solution

Answer

6 coordination sites.

Step 1: Understand what ethylenediaminetetraacetate (EDTA) is

EDTA is a hexadentate ligand, which means it has the ability to bind to a metal ion at six coordination sites.

Step 2: Identify the donor atoms in EDTA

EDTA has four carboxylate groups (–COO-) and two nitrogen atoms (from the amine groups) which act as donor atoms for coordination.

Step 3: Count the coordination sites

Each carboxylate group provides one coordination site through the oxygen atoms, and each nitrogen atom provides one coordination site. Therefore, there are 4 (from oxygen) + 2 (from nitrogen) = 6 coordination sites in total.

Key Concepts

Hexadentate Ligand

EDTA, short for ethylenediaminetetraacetate, is a fascinating example of a hexadentate ligand. In coordination chemistry, the term "hexadentate" describes a ligand that can simultaneously bind to a central metal ion through six points. This characteristic is also described as having six "teeth" with which to grip onto the metal ion, making it a very stable complex. For EDTA, this ability to bind at six sites makes it particularly effective in chelation therapy, where it is used to sequester metal ions. Its hexadentate nature allows it to form strong and stable complexes with metal ions, preventing the metal from reacting further in solutions. This property is highly beneficial in various applications, from industrial to medical, where controlling metal ion activity is crucial.

Donor Atoms

The effectiveness of EDTA as a hexadentate ligand is largely due to its donor atoms. Donor atoms are the specific atoms in the ligand that form coordinate bonds with the metal ion. In the case of EDTA, there are four oxygen atoms, each from a carboxylate group (-COO extsuperscript{-}) and two nitrogen atoms from amine groups. Together, these atoms are responsible for the six coordination sites that can interact with a metal ion.

• Four carboxylate groups contribute four oxygen atoms, each serving as a donor atom.
• Two nitrogen atoms integrate the ligand's structure further, providing the remaining two donor sites.

These donor atoms coordinate with metal ions by sharing their lone pairs, effectively acting as anchors to form a stable complex. Understanding donor atoms is crucial to mastering ligand behavior in coordination chemistry.

Coordination Chemistry

Coordination chemistry is a field focused on understanding how atoms or groups of atoms, known as ligands, interact with metal ions to form complexes. In coordination compounds, the metal ion is termed the "central atom" or "central metal," while the ligands are bound to this metal. EDTA, as a well-known hexadentate ligand, is pivotal to this area of study. When ligands like EDTA bind to metal ions, they form coordinate covalent bonds. This process is crucial because these bonds are both stable and strong, influencing the stability and reactivity of the metal complexes. The study of these interactions helps scientists and chemists design effective and targeted applications, including catalysis, biochemical reactions, and metal detoxification processes. Therefore, understanding coordination chemistry is essential for applying ligands effectively in both laboratory and real-world scenarios.