Structural Isomerism
Isomerism in Coordination Compounds | Class 12
1. Definition
Structural Isomers have the same molecular formula but differ in the nature of bonding (connectivity of atoms) within the coordination sphere.
2. Ionization Isomerism
Arises when the counter ion in the complex salt is itself a potential ligand and can displace a ligand which can then become the counter ion.
- Isomer A: $[Co(NH_3)_5SO_4]Br$ (Red). Gives $Br^-$ ions. Ppt with $AgNO_3$.
- Isomer B: $[Co(NH_3)_5Br]SO_4$ (Violet). Gives $SO_4^{2-}$ ions. Ppt with $BaCl_2$.
3. Hydrate (Solvate) Isomerism
A special type of ionization isomerism where Water ($H_2O$) is involved as a solvent molecule.
Example: $CrCl_3 \cdot 6H_2O$
| Formula | Color | No. of $Cl^-$ Precipitated |
|---|---|---|
| $[Cr(H_2O)_6]Cl_3$ | Violet | 3 |
| $[Cr(H_2O)_5Cl]Cl_2 \cdot H_2O$ | Grey-Green | 2 |
| $[Cr(H_2O)_4Cl_2]Cl \cdot 2H_2O$ | Dark Green | 1 |
4. Linkage Isomerism
Arises in coordination compounds containing Ambidentate Ligands (ligands that can ligate through two different atoms).
- Nitrite Ion ($NO_2^-$):
- Nitro ($M-NO_2$): Bonded through Nitrogen. (Yellow).
- Nitrito ($M-ONO$): Bonded through Oxygen. (Red).
- Thiocyanate ($SCN^-$): $M-SCN$ vs $M-NCS$.
Example: $[Co(NH_3)_5(NO_2)]Cl_2$ and $[Co(NH_3)_5(ONO)]Cl_2$.
5. Coordination Isomerism
Arises in compounds where both Cation and Anion are complex entities. It involves the interchange of ligands between the two coordination spheres.
Examples:
1. $[Co(NH_3)_6][Cr(CN)_6]$
2. $[Cr(NH_3)_6][Co(CN)_6]$
1. $[Co(NH_3)_6][Cr(CN)_6]$
2. $[Cr(NH_3)_6][Co(CN)_6]$
Practice Quiz
Identify the Isomer Type.
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