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Coordination Compounds question

2019 · 10 Jan · Shift 2 · Q9
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Coordination Compounds question

2019 · 10 Jan · Shift 2 · Q9

JEE MainChemistryCoordination CompoundsMCQ+4 / −1
A reaction of cobalt (III) chloride and ethylenediamine in a 1 : 2 mole ratio generates two isomeric products A (violet coloured) and B (green coloured). A can show optical activity, but B is optically inactive. What type of isomers does A and B represcent?
  1. A
    Ionisation isomers
  2. B
    Linkage isomers
  3. C
    Coordination isomers
  4. D
    Geometrical isomers
View written solutionFree

Correct answer: D

  1. Identify the complex formed

Cobalt(III) chloride reacts with ethylenediamine (enenen) in a 1:21:21:2 mole ratio.

Since cobalt is in the +3 oxidation state and enenen is a neutral bidentate ligand, the complex formed is of the type:

[Co(en)2Cl2]+[Co(en)_2Cl_2]^+[Co(en)2​Cl2​]+

with one chloride ion outside the coordination sphere:

[Co(en)2Cl2]Cl[Co(en)_2Cl_2]Cl[Co(en)2​Cl2​]Cl

  1. Possible isomerism in [Co(en)2Cl2]+[Co(en)_2Cl_2]^+[Co(en)2​Cl2​]+

This is an octahedral complex with:

  • two bidentate enenen ligands
  • two monodentate Cl−Cl^-Cl− ligands

Such a complex can show geometrical isomerism:

  • cis-[Co(en)2Cl2]+[Co(en)_2Cl_2]^+[Co(en)2​Cl2​]+
  • trans-[Co(en)2Cl2]+[Co(en)_2Cl_2]^+[Co(en)2​Cl2​]+
  1. Use the optical activity clue

The question says:

  • Product A is violet and can show optical activity
  • Product B is green and is optically inactive

For octahedral complexes of type [M(en)2Cl2]+[M(en)_2Cl_2]^+[M(en)2​Cl2​]+:

  • the cis isomer is chiral and hence can show optical activity
  • the trans isomer has a plane/element of symmetry and is optically inactive

Therefore:

  • A = cis isomer
  • B = trans isomer
  1. Type of isomerism between A and B

Since A and B differ as cis and trans forms, they are:

Geometrical isomers\boxed{\text{Geometrical isomers}}Geometrical isomers​

  1. Check options
  • A: Ionisation isomers — No
  • B: Linkage isomers — No
  • C: Coordination isomers — No
  • D: Geometrical isomers — Yes

Hence, the correct option is:

D\boxed{D}D​

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