Which of the following colour change occurs when tridentate ligand, ethane-1, 2-diamine (en) is progressively added to an aqueous solution of nickel (II) chloride ?

Options

A. Green to pale blue
B. Green to purple blue
C. Green to violet
D. All of these

Answer

D

Explanation

The influence of the ligands on the colour of a complex may be illustrated by considering the `[Ni(H_(2)O)_(6)]^(2+)` complex, which forms when `NiC1_(2)` is dissolved in water. If the bidentate ligand, ethylene diamine (en) is progressively added in the molar rations en: `Ni, 1:1, 2:1, 3:1`, the following series of reactions and their associated colour changes occur:
`[Ni(H_(2)O)_(6)]^(2+) (aq) overset (en(aq)) rarr underset("pale blue")([Ni(H_(2)O)_(4)(en)]^(2+)) (aq) + 2H_(2)O`
`[Ni(H_(2)O)_(4)(en)]^(2+) (aq) overset (en(aq)) rarr underset("blue/purple")([Ni(H_(2)O)_(2)(en)_(2)]^(2+)) + 2H_(2)O`
`[Ni(H_(2)O)_(2)(en)_(2)]^(2+) (aq) overset (en(aq)) rarr underset("violet")([Ni(en)_(3)]^(2+)) (aq) + 2H_(2)O`