Question

A compound Co(en)₂ (NO₂)₂Cl has been prepared in a number of isomeric forms. One form undergoes no reaction with AgNO₃ or (en) and is optically inactive. A second form reacts with AgNO₃ but not with (en) and is optically inactive. A third form is optically active and reacts with both AgNO₃ and (en). Identify each of these isomeric forms. Name and sketch each of the structures. 

Answer 1

Based on reactions with AgNO₃ and (en), and optical activity, isomers can be identified.

First form : There is no reaction with AgNO₃, hence no Cl– ions outside coordination sphere. Also there is no reaction with bidentate (en), hence these ligands are trans to each other. Optical inactivity is also due to trans structure. Thus, it may have structure : 

trans-chloronitrobis (ethylenediamine) cobalt (III) nitrite.

Secon form : In this Cl^– is outside coordination sphere since it reacts with AgNO₃. As in the first form NO₂ ^– ligands are trans to each other being optically inactive. This is represented as, 

trans-bis (ethylenediamine) dinitrocobalt (III) chloride 

Third form : In this case also, Cl^– is outside coordination sphere. Also it shows reaction with (en) hence monodentate ligands are cis to each other. Being optically active, mirror image should not superimpose. Thus, it can have structure : 

cis-bis (ethylenediamine) dinitrocobalt (III) chloride