Question

Facial-meridional isomers are associated with which one of the following complexes?
($M =$central metal)
A) $[M{(AA)_2}]$
B) $\left[ {M{A_3}{B_3}} \right]$
C) $\left[ {M{{\left( {AA} \right)}_3}} \right]$
D) $\left[ {MABCD} \right]$

Answer 1

In the facial type of isomers the same type of ligands are present on the same side. In the case of the meridional type of isomers, one of the ligands on the same side is replaced by another ligand of a different side. One can observe and see which option can give both facial and meridional isomers.

Complete answer:

1. First of all, we will learn about the facial and meridional types of isomers. The facial isomers are the isomers in which the same type of ligands are situated on one side and another same type of ligands are situated on the other side. Let us see how facial isomers look in the image given below.
2. In the case of meridional isomers there is one ligand replaced from the same side ligands by another ligand and this is also done on another side of the ligands. Let us see how meridional isomers look in the image given below.
   Image showing facial isomers and meridional isomers:
   
3. Now let’s analyze the given options and see which can give facial-meridional isomers. In option A $[M{(AA)_2}]$ can not give facial isomers as there are the same ligands present in it. Hence, this option is incorrect.
4. In option B $\left[ {M{A_3}{B_3}} \right]$ has three ligands as A and three ligands as B. They both ligands are different types of ligands and can give both facial and meridional isomers. Hence, this option is the correct choice.
5. In option C $\left[ {M{{\left( {AA} \right)}_3}} \right]$ there is the same type of ligands and in option D $\left[ {MABCD} \right]$ there are four different types of ligands which means both cannot give the facial-meridional isomers.
   Therefore, Facial-meridional isomers are associated with a complex $\left[ {M{A_3}{B_3}} \right]$ which shows option B as the correct choice.

Note:
Facial-meridional isomers are different only at one point of ligand attachment. To give Facial-meridional isomers the complex must have three ligands of one type and another three of another type. Both facial and meridional isomers are applicable for octahedral complexes.