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Question
[Ni(H2O)6]2+ (aq) is green in colour whereas [Ni(H2O)4 (en)]2+ (aq)is blue in colour, give reason in support of your answer.
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Solution
The colour of coordination compound depends upon the type of ligand and dd transition taking place.
H2O is weak field ligand , which causes small splitting, leading to the d-d transition corresponding green colour, however due to the presence of (en) which ia strong field ligand, the splitting is increased. Due to the change in t2g - eg splitting the colouration of the compound changes from green to blue.
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