What is meant by the chelate effect? Give an example.
The chelate effect refers to the observation that chelate complexes tend to be more stable than similar complexes containing unidentate ligands. When a di- or polydentate ligand uses its two or more donor atoms simultaneously to bind a single metal ion, it forms a chelate complex, which has enhanced stability.
For example, EDTA (ethylenediaminetetraacetic acid) is a chelating ligand used in the treatment of lead poisoning. It binds to the lead ions through multiple donor atoms, forming a stable chelate complex that can be removed from the body. Another example is ethylenediamine (en), a bidentate ligand that forms stable chelate complexes like [Co(en)₃]³⁺.
Explanation
The textbook context explicitly states that 'chelate complexes tend to be more stable than similar complexes containing unidentate ligands' - this is the chelate effect. The context provides examples of chelating ligands including EDTA (used in lead poisoning treatment), D-penicillamine, and desferrioxime B. The oxalate ion (C₂O₄²⁻) and ethylenediamine (en) mentioned in complex formulas are also examples of chelating ligands that demonstrate this effect.