Question

Using CFT, write electronic configuration for: (i) \( [CoF_6]^{3-} \) (ii) \( [Co(NH_3)_6]^{3+} \). [At. No. Co=27]

Hint:

Spectrochemical Series: $I^-<Br^-<S^{2-}<SCN^-<Cl^-<F^-<OH^-<C_2O_4^{2-}<H_2O<NCS^-<edta^{4-}<NH_3<en<CN^-<CO$.

Answer 1

Step 1: Understanding the Concept:
Strong field ligands cause pairing of electrons (\( \Delta_o>P \)), while weak field ligands do not (\( \Delta_o<P \)).
Step 2: Detailed Explanation:
\( Co^{3+} \) has a \( 3d^6 \) configuration.
(i) \( [CoF_6]^{3-} \): \( F^- \) is a weak field ligand. It follows Hund's rule, populating both levels before pairing. Configuration: \( t_{2g}^4 e_g^2 \) (High spin).
(ii) \( [Co(NH_3)_6]^{3+} \): \( NH_3 \) is a strong field ligand. It causes pairing in the lower \( t_{2g} \) level. Configuration: \( t_{2g}^6 e_g^0 \) (Low spin).
Step 3: Final Answer:
(i) \( t_{2g}^4 e_g^2 \); (ii) \( t_{2g}^6 e_g^0 \).