Question

The complex that shows Facial - Meridional isomerism is:

• A. \( [Co(NH_3)_3Cl_3] \)
• B. \( [Co(NH_3)_4Cl_2]^+ \)
• C. \( [Co(en)_3]^{3+} \)
• D. \( [Co(en)_2Cl_2]^+ \)

Hint:

Facial and meridional isomerism occur in octahedral complexes where ligands are arranged in distinct ways, resulting in different spatial orientations of ligands.

Answer 1

The Correct Option is A

Facial (fac) and meridional (mer) isomers are types of geometric isomers found in octahedral complexes with the general formula \([MA_3B_3]\). In these complexes, three identical ligands can either be adjacent to each other forming a 'facial' configuration or adjacent to form a 'meridional' configuration. 

1. Understanding the Complex: The complex given is \([Co(NH_3)_3Cl_3]\). Here, the ligands \(NH_3\) (ammine) and \(Cl\) (chloride) are arranged around a cobalt central metal atom. Since there are three identical ammine ligands and three identical chloride ligands, this complex can exhibit fac-mer isomerism.
2. Facial Isomerism: In the facial isomerization, the three ammonia ligands (or chloride ligands) are adjacent to each other, forming one face of the octahedron.
3. Meridional Isomerism: In the meridional isomerization, the three ammonia ligands (or chloride ligands) are arranged in a manner such that they span along the meridian of the octahedron, forming a plane.

Let's analyze why the other complexes do not show fac-mer isomerism:

• \([Co(NH_3)_4Cl_2]^+\) only contains four ammine groups and two chloride ions. Such a configuration can have cis-trans isomerism but not fac-mer as there aren't three identical pairs.
• \([Co(en)_3]^{3+}\) consists of three bidentate ethylenediamine (en) ligands. Bidentate ligands typically do not show fac-mer isomerism due to the linkage of the ligands.
• \([Co(en)_2Cl_2]^+\) includes two bidentate ethylenediamine ligands and two chloride ions. This setup can show cis-trans isomerism but not fac-mer due to the nature of bidentate ligands.

Thus, the correct complex exhibiting facial-meridional isomerism is \([Co(NH_3)_3Cl_3]\).

Answer 2

To determine which complex shows facial-meridional isomerism, we first need to understand what these terms mean:

• Facial (fac) isomerism: In a fac-isomer, three identical ligands occupy adjacent positions at the corners of an octahedral complex. These ligands form one face of an octahedron.
• Meridional (mer) isomerism: In a mer-isomer, three identical ligands occupy positions so that they lie in a plane creating a meridian dividing the octahedron into two equal halves.

Now, let's evaluate the given complexes:

\([Co(NH_3)_3Cl_3]\): This complex can display facial-meridional isomerism as it is an octahedral complex with three amine ligands and three chloride ligands, allowing for both fac-arrangement (three Cl or NH₃ occupy one face) and mer-arrangement (three Cl or NH₃ in a plane).

\([Co(NH_3)_4Cl_2]^+\): This complex cannot exhibit this isomerism as it lacks three identical ligands that could form a face.

\([Co(en)_3]^{3+}\): This complex is homoleptic, consisting of three ethylenediamine (\(en\)) ligands that do not allow for facial-meridional distinction.

\([Co(en)_2Cl_2]^+\): Similar to the above, this complex cannot show facial-meridional isomerism as it has only two Cl ions, preventing the formation necessary for fac-mer isomerism.

Thus, the correct complex that shows facial-meridional isomerism is:

\([Co(NH_3)_3Cl_3]\)