Welcome to Chem Zipper.com......: Why [Ni(CN)4]-2 is colourless while [Ni(H2O)4]-2 although both have +2 oxidation state and 3d*8 configuration ?

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### Why [Ni(CN)4]-2 is colourless while [Ni(H2O)4]-2 although both have +2 oxidation state and 3d*8 configuration ?

In case of [Ni(CN)4]-2 Ni is in +2  and  3d8 configuration but presence of strong ligand (CN) , the two unpaired electron in the 3d orbital pair up thus there is no unpaired electrons present hence it is colourless.

In case of [Ni(H2O)4]+2 Ni is in +2  and  3d8 configuration and two unpaired electrons which  I do not pair up in the presence of weak ligand (H2O) , hence it is colour  due to  d-d transition , red colour light is absorbed and give it complementary  colour green.