The light pink color of [Co (H₂ O)₆]²⁺ and the deep blue color of [CoCl₄]²⁻ are due to · ABC26IN1011
Subject: Inorganic Chemistry · Chapter: Coordination Chemistry · Topic: Coordination Chemistry – General · Exam: CSIR NET DEC 2012 · Marks: 2 · Difficulty: Easy
The light pink color of $\left[\mathrm{Co}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{2+}$ and the deep blue color of $\left[\mathrm{CoCl}_{4}\right]^{2-}$ are due to
(a)MLCT transition in the first and d-d transition in the second
(b)LMCT transition in both
(c)d-d transitions in both.
(d)d-d transition in the first and MLCT transition in the second.
Answer
Answer: C ✓ checked by 4AB · confidence high
Explanation
Both colours are d–d transitions of Co(II) d⁷: weak, Laporte-forbidden in the centrosymmetric octahedral aqua ion (pale pink) and much stronger in the non-centrosymmetric tetrahedral [CoCl₄]²⁻ (deep blue).