Question

In which one of the following complexes the metal ion has \( t_{2g}^3 e_g^2 \) configuration?

• A. \( [Mn(H_2O)_6]^{2+} \)
• B. \( [Fe(H_2O)_6]^{2+} \)
• C. \( [Co(NH_3)_6]^{3+} \)
• D. \( [Ni(H_2O)_6]^{2+} \)

Hint:

For octahedral complexes, high-spin configurations depend on ligand strength. Weak field ligands result in \( t_{2g}^3 e_g^2 \) arrangements in \( d^6 \) metal ions.

Answer 1

The Correct Option is B

Step 1: Determine the Oxidation State and Electron Configuration For each complex, we calculate the oxidation state of the metal and its electron configuration: - (A) \( [Mn(H_2O)_6]^{2+} \) - Mn oxidation state: \( +2 \) - Mn atomic number: \( 25 \) → Electron configuration: \( [Ar] 3d^5 \) - \( t_{2g}^3 e_g^2 \) is not matching. - (B) \( [Fe(H_2O)_6]^{2+} \) - Fe oxidation state: \( +2 \) - Fe atomic number: \( 26 \) → Electron configuration: \( [Ar] 3d^6 \) - In an octahedral field, this configuration corresponds to \( t_{2g}^3 e_g^2 \) for high-spin Fe\(^{2+} \) → Correct choice. - (C) \( [Co(NH_3)_6]^{3+} \) - Co oxidation state: \( +3 \) - Co atomic number: \( 27 \) → Electron configuration: \( [Ar] 3d^6 \) - Ligand \( NH_3 \) is a strong field ligand, leading to a low-spin configuration \( t_{2g}^6 e_g^0 \) → Not matching. - (D) \( [Ni(H_2O)_6]^{2+} \) - Ni oxidation state: \( +2 \) - Ni atomic number: \( 28 \) → Electron configuration: \( [Ar] 3d^8 \) - The \( 3d^8 \) configuration leads to \( t_{2g}^6 e_g^2 \) → Not matching. Conclusion Thus, the correct answer is: \[ [Fe(H_2O)_6]^{2+} \]