Question 1

Why is EDTA called a hexadentate ligand?

Accepted Answer

Denticity counts the donor atoms supplied by one ligand. EDTA binds through four carboxylate oxygen atoms and two amine nitrogen atoms, giving six donor atoms in total, so it is hexadentate.

Question 2

What is the difference between denticity and coordination number?

Accepted Answer

Denticity is the number of donor atoms in one ligand. Coordination number is the total number of ligand donor atoms bonded to the central metal ion, so several monodentate ligands can also give a high coordination number.

Question 3

Why does an EDTA complex usually have an octahedral arrangement?

Accepted Answer

Six donor atoms surround one central metal ion in the usual EDTA complex. The octahedral arrangement distributes these six directions in three dimensions rather than placing all donors in one plane.

Question 4

Is an EDTA chelate a single six-membered ring?

Accepted Answer

No. The usual six-coordinate EDTA chelate contains five 5-membered loops: four N–O rings involving the carboxylate donor arms and one N–N ring through the ethylene bridge. Coordination number six counts metal-to-donor links, not the size of one flat ring.

Question 5

How is haemoglobin related to coordination compounds?

Accepted Answer

Haemoglobin is a conjugated protein whose haem group contains a porphyrin ligand coordinated to Fe2+. This is a biological coordination compound and is distinct from an EDTA complex containing a free Ca2+, Fe3+ or Pb2+ target ion.

Chelation in the Body: EDTA, Lead and the Chelate Ring

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