Question

A reaction of cobalt (III) chloride and ethylenediamine in a 1:2 mole ratio generates two isomeric product A (violet coloured) B (green coloured). A can show optical activity, B is optically inactive. What type of isomers does A and B represent?

• A. Geometrical isomers
• B. Ionisation isomers
• C. Coordination isomers
• D. Linkage isomers

Answer 1

The correct option is A Geometrical isomers

• We know Ethylenediamine is a bidentate ligand and $C{o}^{3+}$ forms an octahedral complex having co-ordination number 6. Here, 2 moles of ethylene diamine can satisfy four co-ordination number. Then the remaining two would be satisfied by existing Chloride ions.
  
• The reaction is,
  

$CoC{l}_3+2C_2{H}_8{N}_2\to \left[CoC{l}_2\right(en{)}_2]Cl$

According to a given ratio, the above product can only be formed. As it says there are two products so another product should be an isomer.

Now the possibility is two Cl ions can be either in cis form or in trans-form. And on seeing this in cis form there is no plane of symmetry and hence it is chiral and optically active and the trans will be optically inactive.

• Hence they are Geometrical isomers of each other.