# Why do isomeric bis-ethylenediamine cobalt complexes react differently?

A compound $\ce{Co(en)2(NO2)2Cl}$ has been prepared in a number of isomeric forms.One form undergoes no reaction with $\ce{AgNO3}$ or $\ce{(en)}$ and is optically inactive.

A second form reacts with $\ce{AgNO3}$ but not with $\ce{(en)}$ and is optically inactive.

A third from is optically active and reacts with both $\ce{AgNO3}$ and $\ce{en}$. Identify each of these isomeric forms. Name and sketch each of the structures.

My attempt:

I understood how to use the information of reaction with $\ce{AgNO3}$ and optical activity but couldn't understand what does reaction with $\ce{en}$ represent (I know $\ce{en }$ means ethylene diamine).

In solution, it is given that, if the compound reacts with en it means monodentate ligands are cis to each other,if not it is trans to each other. I couldn't understand why it is so. please help.

• If the monodentate ligands are cis to each other, then one en may substitute them both, which it does quite willingly. Otherwise it can't. – Ivan Neretin Jan 23 '16 at 7:24
• why is it so? how does being cis or trans affect chemical properties?after all stereoisomers have smae chemical properties. – Ajay Sabarish Jan 23 '16 at 8:39
• Simple geometry. Ethylenediamine occupies two positions in the coordination sphere, and these two positions must be cis. Trans positions won't do, they are just too far apart. – Ivan Neretin Jan 23 '16 at 10:15
• sir,please explain in detail,what does configuration has to do with reaction with ethylene diammine?and and why should ethylene diammine in molecule be trans to each other for external ethylene diammine to react with the compound.? – Ajay Sabarish Jan 23 '16 at 11:53
• I never said that ethylenediamine should (or should not) be trans to each other. This does not even make sense. Likewise, my words don't make sense to you. Sorry, I don't think I can help. – Ivan Neretin Jan 23 '16 at 20:08