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प्रश्न
A solution of [Ni(H2O)6]2+ is green but a solution of [Ni(CN)4]2− is colourless. Explain.
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उत्तर
In [Ni(H2O)6]2+ solution, nickel is Ni2+ and has 3d8 electronic configuration. It has two unpaired electrons, which cannot be paired with weak water ligands. The unpaired electrons show d-d transition in which Ni2+ absorbs red light. Therefore, the complex shows a complementary green colour.
In [Ni(CN)4]2−, nickel also exists as an Ni2+ ion. It also has a 3d8 electronic configuration, in which two unpaired electrons are found, but strong CN− ligands get paired. Hence, in the absence of unpaired electrons, the d-d transition does not occur, and the solution remains colourless.
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