Q30 · CSIR-NET Chemistry, June 2019
Paper: CSIR-NET June 2019 · Subject: Inorganic Chemistry · Chapter: Coordination Chemistry · Topic: Coordination Chemistry – General · Marks: 2 · Difficulty: Easy
The correct set of information is
(a)$\left[\mathrm{Mn}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{2+}: \mu_{\text{observed}} = \mu_{\text{spin}} ;\left[\mathrm{Co}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{3+}:$ Paramagnetic
(b)$\left[\mathrm{Mn}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{2+}: \mu_{\text{observed}} > \mu_{\text{spin}} ;\left[\mathrm{Co}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{3+}:$ Diamagnetic
(c)$\left[\mathrm{Mn}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{2+}: \mu_{\text{observed}} = \mu_{\text{spin}} ;\left[\mathrm{Co}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{3+}:$ Diamagnetic
(d)$\left[\mathrm{Mn}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{2+}: \mu_{\text{observed}} > \mu_{\text{spin}} ;\left[\mathrm{Co}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{3+}:$ Paramagnetic
Answer
Answer: C ✓ checked by 4AB · confidence high
The source book printed A; on checking, C is correct — see the explanation.
Printed A; the aqua Co(III) ion is low-spin, diamagnetic.
Explanation
[Mn(H₂O)₆]²⁺ is high-spin d⁵ (⁶A₁g): no orbital contribution, μ_obs = μ_spin = 5.92 BM. [Co(H₂O)₆]³⁺ is low-spin d⁶ (t₂g⁶) and diamagnetic.
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