Q.Define ligand. Give one example hexadentate ligand.

A ligand is an ion or neutral molecule with at least one lone pair on a donor atom, capable of donating that pair to a central metal to form a coordinate bond. Ligands are classified by denticity — how many donor atoms one ligand uses on the same metal at once. Monodentate ligands ($\text{NH}_3$, $\text{H}_2\text{O}$, $\text{Cl}^-$, $\text{CN}^-$) use one donor atom. Bidentate ligands (ethylenediamine, $\text{en}$; oxalate, $\text{C}_2\text{O}_4^{2-}$) use two donor atoms, forming a ring called a chelate ring. Polydentate ligands use three or more; EDTA$^{4-}$ is hexadentate (2 N + 4 O = 6 donors) and can occupy an entire octahedral coordination sphere by itself. …