Name the following coordination entities and draw the structures of their stereoisomers :
(i) `[Co(en)_(2)Cl_(2)]^(+)` (en = ethane-1,2-diamine
(ii) `[Cr(C_(2)O_(4))_(3)]^(3-)`
(iii) `[ Co(NH_(3))_(3)Cl_(3)]`
(Atomic number Cr = 24 , Co = 27)

Explanation

(i) Dichloridobis (ethan-1,2 diamine) cobalt (iii) ion `[Co(en)_(2)cl_(2)]^(+)`

It may not be out of place to mention here that only cis isomer will show optical activity whereas the trans isomer is optically inactive .
(ii) `[Cr(C_(2)O_(4))_(3)]^(3-)`- Trioxalato Chromate (iii) ion

(iii) [`Co(NH_(3))_(3)Cl_(3)]`. Triamintrichlorido cobalt (iii)

These complexes of the type `MA_(4)X_(2) , MA_(3)X_(3) , MA_(4)XY` exists as cis and trans isomers.