These may be simple ions
such as Cl
–, small molecules such as H2O or NH3, larger molecules
such as H2NCH2CH2NH2 or N(CH2CH2NH2)3 or even macromolecules,
such as proteins When a ligand is bound to a metal ion through a single donor
atom, as with Cl
–, H2O or NH3, the ligand is said to be unidentate When a ligand can bind through two donor atoms as in
H2NCH2CH2NH2 (ethane-1,2-diamine) or C2O4
2– (oxalate), the
ligand is said to be didentate and when several donor atoms are
present in a single ligand as in N(CH2CH2NH2)3, the ligand is said
to be polydentate Ethylenediaminetetraacetate ion (EDTA
4–) is
an important hexadentate ligand