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Coordination Compounds question

2015 · Shift 2 · Q10
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Coordination Compounds question

2015 · Shift 2 · Q10

JEE AdvancedChemistryCoordination CompoundsNumerical+3 / −1
Among the complex ions, [Co(NH2−CH2−CH2−NH2)2Cl2]+[Co(NH_2-CH_2-CH_2-NH_2)_2Cl_2]^+[Co(NH2​−CH2​−CH2​−NH2​)2​Cl2​]+, [CrCl2(C2O4)2]3−[CrCl_2(C_2O_4)_2]^{3-}[CrCl2​(C2​O4​)2​]3−, [Fe(H2O)4)OH)2]+[Fe(H_2O)_4)OH)_2]^+[Fe(H2​O)4​)OH)2​]+, [Fe(NH3)2(CN)4]−[Fe(NH_3)_2(CN)_4]^-[Fe(NH3​)2​(CN)4​]−, [Co(NH2−CH2−CH2−NH2)2(NH3)Cl]2+[Co(NH_2-CH_2-CH_2-NH_2)_2(NH_3)Cl]^{2+}[Co(NH2​−CH2​−CH2​−NH2​)2​(NH3​)Cl]2+ and [Co(NH3)4(H2O)Cl]2+[Co(NH_3)_4(H_2O)Cl]^{2+}[Co(NH3​)4​(H2​O)Cl]2+, the number of complex ions that shows cis-trans isomerism is ‾\underline{\hspace{2cm}}​.
Numerical answer
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Correct answer: 6

To determine the number of complex ions that show cis-trans isomerism, we need to analyze the structure of each complex. Cis-trans isomerism is a type of geometrical isomerism possible in octahedral and square planar complexes, where ligands can be arranged either adjacent (cis, 90° apart in octahedral) or opposite (trans, 180° apart in octahedral) to each other.

All the given complexes have a coordination number of 6 and therefore adopt an octahedral geometry. Let's examine each complex ion individually.

  1. [Co(NH2−CH2−CH2−NH2)2Cl2]+[Co(NH_2-CH_2-CH_2-NH_2)_2Cl_2]^+[Co(NH2​−CH2​−CH2​−NH2​)2​Cl2​]+

    • This complex has the general formula [M(AA)2B2][M(AA)_2B_2][M(AA)2​B2​], where M = Co, AA is the symmetric bidentate ligand ethylenediamine (en), and B is the monodentate ligand Cl.
    • In an octahedral complex of this type, the two B ligands (Cl ions) can be placed either adjacent to each other (cis-isomer) or opposite to each other (trans-isomer).
    • Therefore, [Co(en)2Cl2]+[Co(en)_2Cl_2]^+[Co(en)2​Cl2​]+ shows cis-trans isomerism.

  2. [CrCl2(C2O4)2]3−[CrCl_2(C_2O_4)_2]^{3-}[CrCl2​(C2​O4​)2​]3−

    • This complex has the general formula [MB2(AA)2][MB_2(AA)_2][MB2​(AA)2​], which is the same as [M(AA)2B2][M(AA)_2B_2][M(AA)2​B2​]. Here, M = Cr, AA is the symmetric bidentate ligand oxalate (ox), and B is the monodentate ligand Cl.
    • Similar to the first complex, the two Cl ligands can be arranged in cis or trans positions.
    • Therefore, [CrCl2(C2O4)2]3−[CrCl_2(C_2O_4)_2]^{3-}[CrCl2​(C2​O4​)2​]3− shows cis-trans isomerism.

  3. [Fe(H2O)4(OH)2]+[Fe(H_2O)_4(OH)_2]^+[Fe(H2​O)4​(OH)2​]+

    • This complex has the general formula [MA4B2][MA_4B_2][MA4​B2​], where M = Fe, A=H2OA = H_2OA=H2​O, and B = OH.
    • In this octahedral arrangement, the two B ligands (OH ions) can be located at adjacent positions (cis-isomer) or opposite positions (trans-isomer).
    • Therefore, [Fe(H2O)4(OH)2]+[Fe(H_2O)_4(OH)_2]^+[Fe(H2​O)4​(OH)2​]+ shows cis-trans isomerism.

  4. [Fe(NH3)2(CN)4]−[Fe(NH_3)_2(CN)_4]^-[Fe(NH3​)2​(CN)4​]−

    • This complex has the general formula [MA2B4][MA_2B_4][MA2​B4​], where M = Fe, A=NH3A = NH_3A=NH3​, and B = CN.
    • This is structurally analogous to the [MA4B2][MA_4B_2][MA4​B2​] type. The isomerism is determined by the relative positions of the two A ligands (NH3NH_3NH3​ molecules). They can be cis or trans to each other.
    • Therefore, [Fe(NH3)2(CN)4]−[Fe(NH_3)_2(CN)_4]^-[Fe(NH3​)2​(CN)4​]− shows cis-trans isomerism.

  5. [Co(NH2−CH2−CH2−NH2)2(NH3)Cl]2+[Co(NH_2-CH_2-CH_2-NH_2)_2(NH_3)Cl]^{2+}[Co(NH2​−CH2​−CH2​−NH2​)2​(NH3​)Cl]2+

    • This complex has the general formula [M(AA)2BC][M(AA)_2BC][M(AA)2​BC], where M = Co, AA = en, B=NH3B = NH_3B=NH3​, and C = Cl.
    • Here, we have two different monodentate ligands. Geometrical isomerism arises from the relative positions of these two ligands, B and C.
    • The isomer where NH3NH_3NH3​ and Cl are adjacent (90° apart) is the cis-isomer.
    • The isomer where NH3NH_3NH3​ and Cl are opposite (180° apart) is the trans-isomer.
    • Therefore, [Co(en)2(NH3)Cl]2+[Co(en)_2(NH_3)Cl]^{2+}[Co(en)2​(NH3​)Cl]2+ shows cis-trans isomerism.

  6. [Co(NH3)4(H2O)Cl]2+[Co(NH_3)_4(H_2O)Cl]^{2+}[Co(NH3​)4​(H2​O)Cl]2+

    • This complex has the general formula [MA4BC][MA_4BC][MA4​BC], where M = Co, A=NH3A = NH_3A=NH3​, B=H2OB = H_2OB=H2​O, and C = Cl.
    • Similar to the previous case, the geometrical isomers are determined by the relative positions of the two different monodentate ligands, H2OH_2OH2​O and Cl.
    • They can be adjacent to each other (cis-isomer) or opposite to each other (trans-isomer).
    • Therefore, [Co(NH3)4(H2O)Cl]2+[Co(NH_3)_4(H_2O)Cl]^{2+}[Co(NH3​)4​(H2​O)Cl]2+ shows cis-trans isomerism.

Conclusion: All six of the given complex ions have compositions and geometries that allow for cis-trans isomerism. Counting them, we have:

  1. [Co(en)2Cl2]+[Co(en)_2Cl_2]^+[Co(en)2​Cl2​]+ - Yes
  2. [CrCl2(C2O4)2]3−[CrCl_2(C_2O_4)_2]^{3-}[CrCl2​(C2​O4​)2​]3− - Yes
  3. [Fe(H2O)4(OH)2]+[Fe(H_2O)_4(OH)_2]^+[Fe(H2​O)4​(OH)2​]+ - Yes
  4. [Fe(NH3)2(CN)4]−[Fe(NH_3)_2(CN)_4]^-[Fe(NH3​)2​(CN)4​]− - Yes
  5. [Co(en)2(NH3)Cl]2+[Co(en)_2(NH_3)Cl]^{2+}[Co(en)2​(NH3​)Cl]2+ - Yes
  6. [Co(NH3)4(H2O)Cl]2+[Co(NH_3)_4(H_2O)Cl]^{2+}[Co(NH3​)4​(H2​O)Cl]2+ - Yes

The total number of complex ions that show cis-trans isomerism is 6.

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