Chemistry Q60 – JEE-MAIN 2025

Home Chemistry Coordination CompoundsQuestion #342

The d-orbital electronic configuration of the complex among

[C o (e n)_{3}]^{3 +}

[C o F_{6}]^{3 -}

[M n (H_{2} O)_{6}]^{2 +}

and

[Z n (H_{2} O)_{6}]^{2 +}

that has the highest CFSE is :

Clue 1 of 3: Oxidation State and d-electron Count

Determine the oxidation state of the central metal ion and its d-electron count for each complex.

🥷

Ninja Strategy•Strong Field Ligand Dominance

The highest CFSE is typically found in complexes with strong field ligands that promote low spin configurations, leading to a larger stabilization energy.

🧠 Full Solution Path

Step 1: Determine Oxidation State, d-electron Count, and Spin State for each complex✦ Active

For each complex, identify the oxidation state of the central metal ion, its d-electron configuration, and determine if it's high spin or low spin based on the ligand field strength.

[C o (e n)_{3}]^{3 +} : C o^{3 +} (d^{6}) . en is a strong field ligand ⟹ low spin . Configuration: t_{2 g}^{6} e_{g}^{0} .

[C o F_{6}]^{3 -} : C o^{3 +} (d^{6}) . F^{-} is a weak field ligand ⟹ high spin . Configuration: t_{2 g}^{4} e_{g}^{2} .

[M n (H_{2} O)_{6}]^{2 +} : M n^{2 +} (d^{5}) . H_{2} O is a weak field ligand ⟹ high spin . Configuration: t_{2 g}^{3} e_{g}^{2} .

[Z n (H_{2} O)_{6}]^{2 +} : Z n^{2 +} (d^{10}) . Configuration: t_{2 g}^{6} e_{g}^{4} .

Step 2: Calculate CFSE for each complex○ Expand

Calculate the CFSE for each complex. The highest CFSE corresponds to the most negative value (largest magnitude).

[C o (e n)_{3}]^{3 +} : C F S E = (- 0.4 \times 6 + 0.6 \times 0) Δ_{o} + 3 P = - 2.4 Δ_{o} + 3 P .

[C o F_{6}]^{3 -} : C F S E = (- 0.4 \times 4 + 0.6 \times 2) Δ_{o} = (- 1.6 + 1.2) Δ_{o} = - 0.4 Δ_{o} .

[M n (H_{2} O)_{6}]^{2 +} : C F S E = (- 0.4 \times 3 + 0.6 \times 2) Δ_{o} = (- 1.2 + 1.2) Δ_{o} = 0.

[Z n (H_{2} O)_{6}]^{2 +} : C F S E = (- 0.4 \times 6 + 0.6 \times 4) Δ_{o} = (- 2.4 + 2.4) Δ_{o} = 0.

💡 Teacher's Secret Hint

Remember to include pairing energy (P) for low spin complexes when calculating total CFSE, but for comparing magnitude, focus on the $Δ_{o}$ term.

Step 3: Identify the complex with the highest CFSE and its configuration○ Expand

Comparing the CFSE values, $[C o (e n)_{3}]^{3 +}$ has the largest negative CFSE (magnitude $2.4 Δ_{o}$ ), indicating the highest stabilization. Its d-orbital electronic configuration is $t_{2 g}^{6} e_{g}^{0}$ .

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Chemistry Question 60 – JEE-MAIN 2025

Clue 1 of 3: Oxidation State and d-electron Count

🧠 Full Solution Path