The coordination chemistry of EDTA ethylene diamine tetraacetic acid plays a crucial role in its ability to selectively chelate toxic metal ions in chelation therapy. EDTA is a hexadentate ligand, meaning it can form six coordination bonds with a central metal ion. This is due to the presence of four carboxylate groups and two amine groups in its structure, which can donate electron pairs to form coordinate covalent bonds with metal ions.The selectivity of EDTA in chelating toxic metal ions can be attributed to several factors:1. Size and geometry: The size and geometry of EDTA allow it to form stable complexes with metal ions that have a specific size and coordination geometry. Toxic metal ions, such as lead, cadmium, and mercury, often have a suitable size and geometry that allows them to form stable complexes with EDTA.2. Hard-soft acid-base HSAB theory: According to the HSAB theory, hard acids prefer to bind with hard bases, and soft acids prefer to bind with soft bases. EDTA is considered a hard base due to its oxygen and nitrogen donor atoms. Toxic metal ions like lead, cadmium, and mercury are considered borderline or soft acids, which can still form stable complexes with hard bases like EDTA.3. Formation constants: The stability of metal-EDTA complexes is determined by their formation constants Kf . Higher Kf values indicate more stable complexes. EDTA forms more stable complexes with toxic metal ions like lead, cadmium, and mercury compared to essential metal ions like calcium and magnesium. This selectivity helps in the removal of toxic metal ions from the body without significantly affecting the levels of essential metal ions.4. Competition with other ligands: In biological systems, metal ions are often bound to other ligands, such as proteins and enzymes. The high formation constants of EDTA-metal complexes allow EDTA to outcompete these native ligands and bind to the toxic metal ions, facilitating their removal from the body.In summary, the coordination chemistry of EDTA, along with factors such as size and geometry, HSAB theory, formation constants, and competition with other ligands, enables it to selectively chelate toxic metal ions in chelation therapy. This property of EDTA is crucial in the treatment of heavy metal poisoning and the removal of toxic metal ions from the body.