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

💡 Solution & Explanation

# Solution: Identifying Paramagnetic Complex Ions To determine paramagnetism, we need to check for **unpaired electrons** in the d-orbitals of the metal center. **Key principle:** Paramagnetic complexes have unpaired electrons; diamagnetic complexes have all electrons paired. ## General approach: 1. **Identify the metal** and its oxidation state 2. **Count d-electrons** using: $\text{d}^n = (\text{atomic number}) - (\text{oxidation state})$ 3. **Determine electron configuration** in the d-orbitals (depends on ligand field strength) 4. **Count unpaired electrons** — if > 0, the complex is paramagnetic ## Common paramagnetic cases: - **Transition metals in high-spin configuration** with weak field ligands ($H_2O$, halides): unpaired electrons remain - **Odd number of d-electrons**: always paramagnetic (e.g., $d^1, d^3, d^5, d^7, d^9$) - **Even d-electrons in high-spin**: may have unpaired pairs ## Without seeing the options: **Option B is likely a complex with:** - Unpaired d-electrons (e.g., $[Fe(H_2O)_6]^{2+}$ with $d^6$ high-spin has 4 unpaired electrons) - Or an odd number of d-electrons (e.g., $[Cr(H_2O)_6]^{3+}$ with $d^3$ has 3 unpaired electrons) While diamagnetic options would show strong field ligands like $CN^-$ or $CO$ creating low-spin pairing (all electrons paired).