Q35 · CSIR-NET Chemistry, June 2019
Paper: CSIR-NET June 2019 · Subject: Inorganic Chemistry · Chapter: Coordination Chemistry · Topic: Coordination Chemistry – General · Marks: 2 · Difficulty: Hard
Correct order of molar extinction coefficient values of the visible absorption bands for the following species is
(a)$\left[\mathrm{Cr}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{2+}>\left[\mathrm{Mn}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{2+}>$ Chlorophyll $>\left[\mathrm{NiCl}_{4}\right]^{2-}$
(b)Chlorophyll $>\left[\mathrm{NiCl}_{4}\right]^{2-}>\left[\mathrm{Cr}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{2+}>\left[\mathrm{Mn}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{2+}$
(c)$\left[\mathrm{NiCl}_{4}\right]^{2-}>$ Chlorophyll $>\left[\mathrm{Cr}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{2+}>\left[\mathrm{Mn}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{2+}$
(d)Chlorophyll $>\left[\mathrm{Cr}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{2+}>[\mathrm{NiCl}]^{2-}>\left[\mathrm{Mn}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{2+}$
Answer
Answer: B ✓ checked by 4AB · confidence high
Explanation
ε: chlorophyll (allowed π–π*, ~10⁵) > tetrahedral [NiCl₄]²⁻ (~10²) > [Cr(H₂O)₆]²⁺ (Laporte-forbidden) > [Mn(H₂O)₆]²⁺ (also spin-forbidden) (b).
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