Question

In which of the following set of complex ion first can show structural isomerism and second one can show geometrical as well as optical isomerism?

• A. Set-I: $[Co(en)_2NO_2Cl]Br$ and $[PtCl_2(en_2)]^{2+}$
• B. Set-II: $[Co(NH_3)_4Cl_2]Br$ and $[Ni(Gly)_3]^-$
• C. Set-III: $Na_4[Fe(CN)_5NOS]$ and $[Co(en)(NH_3)_4]Cl_2$
• D. Set-IV: $[Cr(NH_3)_6]Cl_3$ and $[Co(en)_3]Cl_2$

Answer 1

Answer: (A), (B)

Set-I and Set-II only

Answer 2

The question requires identifying a set where the first complex exhibits structural isomerism and the second exhibits both geometrical and optical isomerism.

Analysis of Set-I:

1. First complex: $[Co(en)_2NO_2Cl]Br$

   • Coordination sphere: $[Co(en)_2NO_2Cl]^+$. This is an octahedral complex of the type $[M(AA)_2XY]$.
   • Structural Isomerism: The $NO_2$ ligand can coordinate through Nitrogen (nitro, $-NO_2$) or Oxygen (nitrito, $-ONO$). This is linkage isomerism, a type of structural isomerism.
   • Therefore, the first complex shows structural isomerism.

2. Second complex: $[PtCl_2(en_2)]^{2+}$ (interpreted as $[Pt(en)_2Cl_2]^{2+}$)

   • This is a square planar Platinum(II) complex of the type $M(AA)_2B_2$.

   • Geometrical Isomerism: The two $en$ ligands are bidentate and must be in a cis configuration. The two $Cl$ ligands can be arranged in cis or trans positions. Thus, it exhibits geometrical isomerism (cis and trans isomers).

   • Optical Isomerism: The cis isomer of $M(AA)_2B_2$ square planar complexes is chiral and exhibits optical isomerism. The trans isomer is achiral.

   • Therefore, the second complex shows geometrical and optical isomerism.

   • Conclusion for Set-I: Both conditions are met.

Analysis of Set-II:

1. First complex: $[Co(NH_3)_4Cl_2]Br$

   • Coordination sphere: $[Co(NH_3)_4Cl_2]^+$. This is an octahedral complex of the type $MA_4B_2$.
   • Structural Isomerism: The two $Cl$ ligands can be adjacent (cis) or opposite (trans). This is geometrical isomerism, a type of structural isomerism.
   • Therefore, the first complex shows structural isomerism.

2. Second complex: $[Ni(Gly)_3]^-$

   • Glycine (Gly) is an unsymmetric bidentate ligand ($H_2NCH_2COO^-$). This is an octahedral complex of the type $M(AB)_3$.

   • Geometrical Isomerism: Octahedral complexes of the type $M(AB)_3$ exhibit geometrical isomerism in the form of facial ($fac$) and meridional ($mer$) isomers.

   • Optical Isomerism: Both the fac and mer isomers of $M(AB)_3$ type complexes with unsymmetric bidentate ligands can be chiral and exhibit optical isomerism.

   • Therefore, the second complex shows geometrical and optical isomerism.

   • Conclusion for Set-II: Both conditions are met.

Analysis of Set-III:

1. First complex: $Na_4[Fe(CN)_5NOS]$
   • The ligand $NOS$ can exhibit linkage isomerism, leading to structural isomerism.
2. Second complex: $[Co(en)(NH_3)_4]Cl_2$
   • Coordination sphere: $[Co(en)(NH_3)_4]^{2+}$. This is an octahedral complex of the type $[M(AA)A_4]$.
   • Geometrical Isomerism: In $[M(AA)A_4]$ complexes, the bidentate ligand ($en$) occupies cis positions. The remaining four positions are occupied by identical monodentate ligands ($NH_3$). All four positions for $NH_3$ are equivalent relative to the $en$ ligand. This complex does not exhibit geometrical isomerism.
   • Since the second complex does not show geometrical isomerism, Set-III is invalid.

Analysis of Set-IV:

1. First complex: $[Cr(NH_3)_6]Cl_3$
   • This is an octahedral complex of the type $MA_6$.
   • Structural Isomerism: Complexes of the type $MA_6$ do not exhibit any form of structural isomerism.
   • Since the first complex does not show structural isomerism, Set-IV is invalid.

Final Conclusion: Both Set-I and Set-II satisfy the conditions. Set-I has a first complex showing linkage isomerism (structural) and a second complex showing geometrical and optical isomerism. Set-II has a first complex showing geometrical isomerism (structural) and a second complex showing geometrical and optical isomerism.