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JEE Main 202522 JanuaryEvening Shift
Exam
JEE Main
Year
2025
Date
22 January
Shift
Evening Shift
Subject
Chemistry
Chapter
Coordination Compounds

JEE Main 2025 · 22 January · Evening Shift · Chemistry · Coordination Compounds

The correct order of the following complexes in terms of their...

The correct order of the following complexes in terms of their crystal field stabilization energies is :

Options

  1. A\left[\mathrm{Co}\left(\mathrm{NH}_3\right)_4\right]^{2+} \lt [Co(NH3)6]2+<[Co(en)3]3+<[Co(NH3)6]3+\left[\mathrm{Co}\left(\mathrm{NH}_3\right)_6\right]^{2+} \lt \left[\mathrm{Co}(\mathrm{en})_3\right]^{3+} \lt \left[\mathrm{Co}\left(\mathrm{NH}_3\right)_6\right]^{3+}
  2. B\left[\mathrm{Co}\left(\mathrm{NH}_3\right)_6\right]^{2+} \lt [Co(NH3)6]3+<[Co(NH3)4]2+<[Co(en)3]3+\left[\mathrm{Co}\left(\mathrm{NH}_3\right)_6\right]^{3+} \lt \left[\mathrm{Co}\left(\mathrm{NH}_3\right)_4\right]^{2+} \lt \left[\mathrm{Co}(\mathrm{en})_3\right]^{3+}
  3. C[Co(en)3]3+<\left[\mathrm{Co}(\mathrm{en})_3\right]^{3+} \lt\left[\mathrm{Co}\left(\mathrm{NH}_3\right)_6\right]^{3+} \lt \left[\mathrm{Co}\left(\mathrm{NH}_3\right)_6\right]^{2+} \lt \left[\mathrm{Co}\left(\mathrm{NH}_3\right)_4\right]^{2+}
  4. D\left[\mathrm{Co}\left(\mathrm{NH}_3\right)_4\right]^{2+} \lt [Co(NH3)6]2+<[Co(NH3)6]3+<[Co(en)3]3+\left[\mathrm{Co}\left(\mathrm{NH}_3\right)_6\right]^{2+} \lt \left[\mathrm{Co}\left(\mathrm{NH}_3\right)_6\right]^{3+} \lt \left[\mathrm{Co}(\mathrm{en})_3\right]^{3+}

Correct answer

D. \left[\mathrm{Co}\left(\mathrm{NH}_3\right)_4\right]^{2+} \lt [Co(NH3)6]2+<[Co(NH3)6]3+<[Co(en)3]3+\left[\mathrm{Co}\left(\mathrm{NH}_3\right)_6\right]^{2+} \lt \left[\mathrm{Co}\left(\mathrm{NH}_3\right)_6\right]^{3+} \lt \left[\mathrm{Co}(\mathrm{en})_3\right]^{3+}

Step-by-step solution

Crystal field splitting energy (Δ)∝(\Delta) \propto charge or oxidation state of central metal atom. Crystal field splitting energy (Δ)∝(\Delta) \propto Field strength of ligand (and chelation) Crystal field stabilisation energy (CFSE) =[−0.4tgg=\left[-0.4 \mathrm{t}_{\mathrm{g}_g}\right. +0.6 eg] Δ∘\Delta_{\circ} (for octahedral) For, [Co(en)3]3+:Co3+:t2 g6eg0;CFSE=−2.4(Δ0)1[Co(NH3)6]3+:Co3+:t2 g6eg0;CFSE=−2.4(Δ0)2[Co(NH3)6]2+:Co2+:t2g5eg2;CFSE=−0.8(Δ0)3[Co(NH3)4]2+:Co2+:e4t23;CFSE=−1.2Δt(as:(Δt)=49(Δ0)3)∵Δt<(Δ0)3<(Δ0)2<(Δ0)1\begin{aligned} & {\left[\mathrm{Co}(\mathrm{en})_3\right]^{3+}: \mathrm{Co}^{3+}: \mathrm{t}_{2 \mathrm{~g}}^6 \mathrm{eg}^0 ; \mathrm{CFSE}=-2.4\left(\Delta_0\right)_1} \\ & {\left[\mathrm{Co}\left(\mathrm{NH}_3\right)_6\right]^{3+}: \mathrm{Co}^{3+}: \mathrm{t}_{2 \mathrm{~g}}^6 \mathrm{eg}^0 ; \mathrm{CFSE}=-2.4\left(\Delta_0\right)_2} \\ & {\left[\mathrm{Co}\left(\mathrm{NH}_3\right)_6\right]^{2+}: \mathrm{Co}^{2+}: \mathrm{t}_{2 g}^5 \mathrm{eg}^2 ; \mathrm{CFSE}=-0.8\left(\Delta_0\right)_3} \\ & {\left[\mathrm{Co}\left(\mathrm{NH}_3\right)_4\right]^{2+}: \mathrm{Co}^{2+}: \mathrm{e}^4 \mathrm{t}_2^3 ; \mathrm{CFSE}=-1.2 \Delta_{\mathrm{t}}} \\ & \left(\mathrm{as}:\left(\Delta_{\mathrm{t}}\right)=\frac{4}{9}\left(\Delta_0\right)_3\right) \\ & \because \quad \Delta_{\mathrm{t}} < \left(\Delta_0\right)_3 < \left(\Delta_0\right)_2 < \left(\Delta_0\right)_1\end{aligned}
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