Question

What type of isomerism exists in the following pairs of complexes?
(i) $ [Co(NH_{3})_{5}NO_{3}]SO_{4}$ and $[Co(NH_{3})_{5}SO_{4})NO_{3}$
(ii) $[Co(en)(H_{2}O )_{2}Cl_{2}]Cl$ and $[Co(en)(H_{2}O)Cl_{3}]H_{2}O$

• A. (i) Ionisation (ii) Hydrate
• B. (i) Linkage (ii) Hydrate
• C. (i) Ionisation (ii) Linkage
• D. (i) Linkage (ii) Coordination

Answer 1

Answer: (A)

(i) $\left[ Co \left( NH _{3}\right)_{5} NO _{3}\right] SO _{4}$ and $\left[ Co \left( NH _{3}\right)_{5} SO _{4}\right] NO _{3}$ shows ionisation isomerism. A ligand and an anion are exchanged.
In aqueous solution, $\left[ Co \left( NH _{3}\right)_{5} NO _{3}\right] SO _{4}$ dissociates to give sulphate ions which react with barium chloride to give white ppt of barium sulphate and the complex ions contain nitrate ligand.
In aqueous solution, $\left[ Co \left( NH _{3}\right)_{5} SO _{4}\right] NO _{3}$ dissociates to give nitrate ions and the complex ion contains sulphate ligand.
(ii) $\left[ Co ( en )\left( H _{2} O \right)_{2} Cl _{2}\right] Cl$ and $\left[ Co ( en )\left( H _{2} O \right) Cl _{3}\right] H _{2} O$ shows hydrate isomerism. Water molecules are exchanged inside and outside coordination sphere.
The number of water molecules is different inside and outside the coordination sphere.
$\left[ Co ( en )\left( H _{2} O \right)_{2} Cl _{2}\right] Cl$ has two water molecules inside the coordination sphere and zero water molecules outside the coordination sphere.
$\left[ Co ( en )\left( H _{2} O \right) Cl _{3}\right] H _{2} O$ has one water molecule inside coordination sphere and one water molecule outside coordination sphere.