( c ) Ligands
The ions or molecules bound to the central atom/ion in the
coordination entity are called ligands 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