Question:

The existence of two different coloured complexes with the composition of $[Co(NH_3 )_4Cl_2 ]^+$ is due to

Updated On: Jul 29, 2022
  • linkage isomerism
  • geometrical isomerism
  • coordination isomerism
  • ionisation isomerism
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The Correct Option is B

Solution and Explanation

Complexes of $[MA_4B_2]$ type exhibit geometrical isomerism. The complex $[Co(NH_3)_4Cl_2]+ is a [MA_4B_2]$ type complex and thus, fulfills the conditions that are necessary to exhibit geometrical isomerism. Hence, it has two geometrical isomers of different colours as : The structure of the geometrical isomers is as For linkage isomerism, presence of ambidentate ligand is necessary. For coordination isomerism, both the cation and anion of the complex must be complex ions. For ionisation isomerism, an nion different to the ligands must be present outside the coordination sphere. All these conditions are not satisfied by this complex. Hence, it does not exhibit other given isomerisms.
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Concepts Used:

Isomerism in Coordination Compounds

Isomers in Coordination Compounds

Stereoisomers occur when the ligands have the same bonds, but the bonds are in different orientations relative to one another. Structural isomerism occurs when the bonds are different. Isomers are distinct compounds that can have different physical properties such as color, crystal structure, and melting point.

Cis and Trans Stereoisomers

In octahedral complexes—with four of one ligand and two of another—and square planar complexes—with two of one ligand and two of another—there are two different arrangements of the same atoms with the same bonds. These different arrangements are called cis and trans. In cis molecules, the two ligands are on the same side of the complex. In trans molecules, the similar ligands are on the opposite sides of the molecules, meaning the bond angle is 180 degrees.

Optical Stereoisomers

Optical isomerism occurs when a molecule is not superimposable with its mirror image. 

Fac and Mer Stereoisomers

When three identical ligands occupy one face of an octahedron, the isomer is said to be facial or fac. If these three ligands and the metal ion are in one plane, the isomer is said to be meridional or mer.