Coordination Compounds Part 2

A. Coordination isomerisms occurs in coordination salts in which there is an interchange of ligands between the metal in the cationic coordination spheres and the metal in the anionic coordination sphere. $[\mathrm{Co}(\mathrm{NH}_3)_6][\mathrm{Cr}(\mathrm{CN})_6]\Leftrightarrow[\mathrm{Co}(\mathrm{CN})_6][\mathrm{Cr}(\mathrm{NH}_3)_6]$ (Coordinate isomerism) B. Linkage isomerism occurs in coordination compounds that have the same composition but differ in the connectivity of the ligand to the metal. $[\mathrm{Co}(\mathrm{NH}_3)_3(\mathrm{NO}_2)_3]$ shows linkage isomerism. $\mathrm{NO}_2$ can connect through $\mathrm{N}$ and $\mathrm{O}$ donor sites. C. Solvate isomerism is also known as 'hydrate isomerism' where water behaves as a ligand and water of crystallisation. e.g., The complex $[\mathrm{Cr}(\mathrm{H}_2\mathrm{O})_6]\mathrm{Cl}_3$ (violet) contains water as a ligand and its solvate isomer $[\mathrm{Cr}(\mathrm{H}_2\mathrm{O})_5\mathrm{Cl}]\mathrm{Cl}_2\mathrm{H}_2\mathrm{O}$ (grey- green) contain water as a water of crystallisation. D. Optical isomerism occurs mainly in compounds that are mirror images of each other. $\text{cis}[\mathrm{CrCl}_2(\mathrm{ox})_2]^{3+}$ is chiral compound, hence shows optical isomerism.