Which of the following octahedral complex ions is diamagnetic? — Coordination Compounds Chemistry Question

💡 Solution & Explanation

I need to see the options to provide a complete solution. However, I can explain the general approach for identifying diamagnetic octahedral complexes: **Key Concept:** A complex is diamagnetic when all electrons are paired (no unpaired electrons). **General Steps:** 1. **Identify the metal ion and its d-electron configuration** in the free state 2. **Determine the oxidation state** of the metal in the complex 3. **Apply crystal field splitting** for octahedral geometry ($d_{z^2}$ and $d_{x^2-y^2}$ split higher; $d_{xy}$, $d_{xz}$, $d_{yz}$ split lower) 4. **Fill electrons following Hund's rule** (for weak-field ligands) or **pairing** (for strong-field ligands like $CN^-$, $CO$) 5. **Count unpaired electrons:** If zero → diamagnetic; if >0 → paramagnetic **Example:** $[Fe(CN)_6]^{4-}$ - Fe: $d^6$, strong-field ligand $CN^-$ causes pairing - Configuration: $t_{2g}^6e_g^0$ → all paired → **diamagnetic** ✓ Common diamagnetic octahedral complexes: - $[Fe(CN)_6]^{4-}$ ($d^6$, low-spin) - $[Co(NH_3)_6]^{3+}$ ($d^6$, low-spin) - $[Zn(NH_3)_6]^{2+}$ ($d^{10}$) - $[Pt(NH_3)_6]^{2+}$ ($d^8$, square planar but relevant) **Please share option A** so I can confirm why it's diamagnetic and rule out the others.