Question
List various types of isomerism possible for coordination compounds, giving an example of each.
Solution
(i) Ionisation isomerism: This type of isomerism occurs when there is an interchange of groups between the co-ordination sphere of the metal ion and ions outside this sphere, e.g.,
are ionisation isomers.
(ii) Coordination isomerism: This type of isomerism occurs when both the cation and anion are complexes and they differ in the coordination of ligands, e.g., [Co(NH3)6][Cr(C2O4)3] and [Cr(NH3)6] [Co(C2O4)3] are coordination isomers.
(iii) Linkage isomerism: The isomerism in which a ligand can form linkage with metal through different atoms, e.g., nitro group can link to metal either through nitrogen (–NO2) or through oxygen atom, e.g.,
and
are linkage isomers.
(iv) Geometrical isomerism: In tetra coordinated square planar complexes, cis- (when same groups are on same side and trans- (when same groups are on opposite sides) isomers are possible depending on position of different ligands, e.g., cis-platin and trans-diamine dichloro platinum(II).
Fig. Geometrical isomerism.
(v) Optical isomerism: Optical isomers are those which are not superimposable on their mirror images. Complexes with coordination number six, having bidentate ligands provide examples of optical isomerism, e.g.,
Fig. Optical isomerism.
are ionisation isomers.
(ii) Coordination isomerism: This type of isomerism occurs when both the cation and anion are complexes and they differ in the coordination of ligands, e.g., [Co(NH3)6][Cr(C2O4)3] and [Cr(NH3)6] [Co(C2O4)3] are coordination isomers.
(iii) Linkage isomerism: The isomerism in which a ligand can form linkage with metal through different atoms, e.g., nitro group can link to metal either through nitrogen (–NO2) or through oxygen atom, e.g.,
and
are linkage isomers.
(iv) Geometrical isomerism: In tetra coordinated square planar complexes, cis- (when same groups are on same side and trans- (when same groups are on opposite sides) isomers are possible depending on position of different ligands, e.g., cis-platin and trans-diamine dichloro platinum(II).
Fig. Geometrical isomerism.
(v) Optical isomerism: Optical isomers are those which are not superimposable on their mirror images. Complexes with coordination number six, having bidentate ligands provide examples of optical isomerism, e.g.,
Fig. Optical isomerism.
