Question

Which of the following shows the maximum number of geometrical isomers?

• A. ${[Co(en)3]^3+} $
• B. ${[CoCl2(en)2]^+} $
• C. ${[CoCl2(NH3)4]^+} $
• D. ${[Co(NH3)3Cl3]} $

Hint:

Geometrical Isomerism in Coordination Compounds.

• Octahedral complexes with multiple types of monodentate ligands can show cis/trans or fac/mer isomerism.
• Bidentate ligands usually limit geometrical isomerism due to rigidity.
• [Co(NH3)3Cl3] has 3 NH$_3$ and 3 Cl, allowing multiple arrangements.

Answer 1

The Correct Option is D

Let’s analyze the possibility of geometrical isomerism:

• \([Co(en)_3]^{3+}\): No geometrical isomerism due to symmetrical bidentate ligands and octahedral symmetry. Only optical isomers are possible.
• \([CoCl_2(en)_2]^+\): Has two bidentate and two monodentate ligands; shows cis-trans isomerism. Total = 2 geometrical isomers.
• \([CoCl_2(NH_3)_4]^+\): Four identical and two different ligands → cis-trans isomerism → 2 geometrical isomers.
• \([Co(NH_3)_3Cl_3]\): 3 Cl and 3 NH₃ → shows fac-mer and cis-trans isomerism → maximum 3 geometrical isomers.

Hence, \([Co(NH_3)_3Cl_3]\) shows the maximum number of geometrical isomers.

Answer 2

Step 1: Understand geometrical isomerism in coordination complexes
Geometrical isomers occur when ligands can be arranged differently in space around the central metal atom, leading to different spatial arrangements without changing the connectivity.

Step 2: Analyze the given complexes
For octahedral complexes with formula \([Co(NH_3)_3Cl_3]\), where there are three identical ligands of each type, multiple geometrical isomers are possible due to different arrangements of the ligands around cobalt.
Common geometrical isomers for this complex include facial (fac) and meridional (mer) isomers.

Step 3: Comparison with other complexes
Complexes with fewer or symmetrical ligands usually have fewer geometrical isomers.
For example, complexes with formulae like \([Ni(CO)_4]\) are tetrahedral and do not show geometrical isomerism.

Step 4: Conclusion
Among the options, \([Co(NH_3)_3Cl_3]\) shows the maximum number of geometrical isomers due to the possible fac and mer arrangements of the three identical NH₃ and three Cl ligands around cobalt in an octahedral geometry.