A chelating agent has two or more than two donor atoms to bind to a single metal ion. Which of the following is not a chelating agent?

Options

A. Thiosulphato
B. Oxalato
C. Glycinato
D. Ethane-1 , 2- diamine

Explanation

To determine which of the following is not a chelating agent, we first need to understand what a chelating agent is. A chelating agent is a molecule that can form multiple bonds to a single metal ion. This typically involves the presence of two or more donor atoms that can coordinate to the metal ion, forming a stable ring structure.

Let's analyze the options provided:

1. **Thiosulfate (S2O3^2-)**: Thiosulfate has a structure that does not allow it to effectively bind to a metal ion through multiple donor atoms. The geometry of thiosulfate is not favorable for chelation, as it lacks sufficient donor atoms that can simultaneously coordinate to a single metal ion.

2. **Oxalate (C2O4^2-)**: Oxalate is a well-known bidentate ligand, meaning it has two donor atoms (both oxygen atoms) that can bind to a metal ion. It forms stable chelate complexes with many metal ions.

3. **Glycinate (NH2CH2COO^-)**: Glycinate is also a bidentate ligand, with one donor atom being nitrogen and the other being oxygen. It can effectively bind to a metal ion through these two sites, making it a chelating agent.

4. **Ethane-1,2-diamine (C2H8N2)**: Ethane-1,2-diamine is another bidentate ligand, where both donor atoms are nitrogen. It can bind to a metal ion through these two nitrogen atoms, forming a chelate complex.

After analyzing all the options, we can conclude that:

- **Thiosulfate is not a chelating agent** because it does not have a favorable geometry to bind effectively to a metal ion through multiple donor atoms.

Thus, the correct answer is **option 1: Thiosulfate**.