Question

Explain unidentate and bidentate ligands giving examples.

Hint:

Chelating (multidentate) ligands enhance stability of complexes via the chelate effect. Unidentate ligands bind only at one site, but bidentate ligands form stable rings by binding at two sites.

Answer 1

Unidentate ligands:
- These are ligands that have only one donor atom for coordination with the central metal ion.
- They donate a single lone pair of electrons.
Examples: $\mathrm{H_2O}$ (aqua), $\mathrm{NH_3}$ (ammine), $\mathrm{Cl^-}$ (chloro), $\mathrm{CN^-}$ (cyano).
\[ [\mathrm{Co(NH_3)_6}]^{3+}, [\mathrm{CuCl_4}]^{2-} \] Bidentate ligands:
- These ligands possess two donor atoms which can coordinate to a single metal ion simultaneously.
- They form chelate rings with the central atom, increasing stability of the complex.
Examples: $\mathrm{C_2O_4^{2-}}$ (oxalato, donor O atoms), $\mathrm{en}$ (ethylenediamine, donor N atoms).
\[ [\mathrm{Co(en)_3}]^{3+}, [\mathrm{Fe(C_2O_4)_3}]^{3-} \] \[ \boxed{\text{Unidentate ligands bind through one atom, bidentate ligands through two atoms.}} \]