Coordination Compounds Part 3

If ethane-1,2-diamine (en) is added progressively to an aqueous solution of NiCl2 in the molar ratios en : Ni 1:1,2:1 and 3:1, the following series of reactions and their associated colour changes occur.
[N‌

[Ni(H2O)6.

‌ Green ‌

]2+(aq)+en(aq)→

[Ni(H2O)4en]2+

Pale‌blue

(aq)+2H2O