Question

The observed magnetic moments of octahedral Mn$^{3+}$, Fe$^{3+}$ and Co$^{3+}$ complexes are 4.95, 6.06 and 0.00 BM, respectively. The correct option for the electronic configuration of Mn$^{3+}$, Fe$^{3+}$ and Co$^{3+}$ metal ions in these complexes, respectively, is

• A. t$_{2g}^6$ e$_g^0$, t$_{2g}^5$ e$_g^1$ and t$_{2g}^6$ e$_g^0$
• B. t$_{2g}^6$ e$_g^1$, t$_{2g}^5$ e$_g^0$ and t$_{2g}^6$ e$_g^1$
• C. t$_{2g}^6$ e$_g^0$, t$_{2g}^6$ e$_g^1$ and t$_{2g}^5$ e$_g^1$
• D. t$_{2g}^5$ e$_g^1$, t$_{2g}^6$ e$_g^1$ and t$_{2g}^6$ e$_g^0$

Hint:

Magnetic moments are determined by the number of unpaired electrons in the complex. For octahedral complexes, the configuration of the t$_{2g}$ and e$_g$ orbitals governs the magnetic behavior.

Answer 1

The Correct Option is C

Step 1: Electronic configuration of the complexes. 
- Mn$^{3+}$: It has 5 d-electrons, so the configuration will be t$_{2g}^6$ e$_g^0$ (with no unpaired electrons in the e$_g$ orbitals, resulting in a low magnetic moment). 
- Fe$^{3+}$: It has 5 d-electrons, so the configuration will be t$_{2g}^5$ e$_g^1$ (resulting in an unpaired electron in the e$_g$ orbital, giving a high magnetic moment). 
- Co$^{3+}$: It has 6 d-electrons, so the configuration will be t$_{2g}^6$ e$_g^0$ (with paired electrons in the e$_g$ orbitals, giving no magnetic moment). 
Step 2: Conclusion. 
The correct electronic configuration for Mn$^{3+}$, Fe$^{3+}$ and Co$^{3+}$ ions is option (A).