Question

Explain co-ordination and ionisation isomeristmes with a suitable example for each.

Answer 1

(i) Co-ordination isomerism : In a bimetallic complex, die distribution of ligands between the two co-ordination spheres can differ, giving rise to isomers called the co-ordination isomers. This phenomenon is called as co-ordination isomerism. This isomerism is explained by the following pairs of complexes Where the complex cation and anion have different metal centres.
a) $\underset{Cobalt\left(III\right)}{\underset{Hextunmine}{\left[C{O}^{III}\right(N{H}_3{)}_6]}}\underset{Chromate\left(III\right)}{\underset{Hertacyano}{\left[Cr\right(CN{)}_6]}}$
and
$\underset{Chromium\left(III\right)}{\underset{Hextunmine}{\left[C{r}^{III}\right(N{H}_3{)}_4]}}\underset{Cobatate\left(III\right)}{\underset{Hertacyano}{\left[C{O}^{III}\right(CN{)}_6]}}$
b)$\underset{Platinum\left(II\right)}{\underset{Tetraammine}{\left[P{t}^{II}\right(N{H}_3{)}_4]}}\underset{Cuparate\left(II\right)}{\underset{Tetrachloro}{\left[CuC{l}_4\right]}}$
and
$\underset{Copper\left(II\right)}{\underset{Tetraammine}{\left[Cu\right(N{H}_3{)}_4]}}\underset{Platinate\left(II\right)}{\underset{Tetrachloro}{\left[PtC{l}_4\right]}}$
In the above isomers, the interchange ligands in the co-ordination spheres of cationic and anionic parts takes place and leads to obtain co-ordination isomerism.
ionisation isomerism: Co-ordination compounds containing the same molecular formula but rotating various ions in solution are called ionisation isomers. This property is known as ionisation isomerism.
In this type ofisomerism the diffarontearises from the interchange of groups within or outside the co-ordination sphere.
E.g, : This type of isomerism is furnished by the red-violet
$\left[Co\right(N{H}_3{)}_{5}Br]S{O}_4$
pentaamminebromocobat (III) sulphate
$\left[CO\right(N{H}_3{)}_{5}S{O}_4]Br$
pentaamminesulphatocobalt (III) bromide
Red violet isomer gives sulphate, ion and red isomer furnishes bromide ion in solution.