Question

What is the color of the complex \([Ni(en)_3]^{2+}\) in water?

• A. Pale blue
• B. Purple
• C. Violet
• D. Green
• E. Orange

Hint:

The color of a coordination complex is related to the d-d transitions in the metal's d-orbitals, and the nature of the ligand field significantly influences the absorption of light.

Answer 1

The Correct Option is C

The color of coordination complexes depends on the nature of the metal-ligand interactions and the ligand field. The Ni(II) ion in the complex \([Ni(en)_3]^{2+}\) (where en is ethylenediamine, a bidentate ligand) results in a violet color due to the d-d transitions in the metal's d-orbitals.
- Option (A): Pale blue is often associated with Cu(II) complexes, but not with \([Ni(en)_3]^{2+}\).
- Option (B): Purple is also not typically the color of \([Ni(en)_3]^{2+}\).
- Option (C): Violet is the correct color for \([Ni(en)_3]^{2+}\), as the complex exhibits d-d transitions that absorb light in the visible spectrum.
- Option (D): Green is more commonly observed in some Ni(II) complexes, but not for \([Ni(en)_3]^{2+}\).
- Option (E): Orange is not typical for Ni(II) complexes, which are more often violet or green.
Thus, the correct answer is (C) Violet, as \([Ni(en)_3]^{2+}\) appears violet in water.