# Step-by-Step Solution ## **Step 1: Recall the Jahn-Teller Effect** - The Jahn-Teller effect states that **any non-linear molecule with a degenerate electronic ground state will undergo a distortion to remove that degeneracy and lower its energy.** - In octahedral complexes, this is most often seen with d⁹, high-spin d⁴, and low-spin d⁷ electron configurations. --- ## **Step 2: Analyze Each Complex** ### (i) **[Cr(CN)₆]³⁻** - **Cr oxidation state:** CN = -1 (x 6 = -6), total = -3 Let Cr = x \( x + (-6) = -3 \implies x = +3 \) - **Cr³⁺ configuration:** Atomic: [Ar] 3d⁵ 4s¹ Cr³⁺: Remove 3 electrons → [Ar] 3d³ - **CN⁻ is a strong field ligand:** Causes pairing of electrons (low-spin complex). - **Electronic configuration in octahedral field (t₂g, e_g):** 3 electrons in t₂g orbitals (t₂g³ e_g⁰), fully filled t₂g, no degeneracy. - **Jahn-Teller distortion?** **NO**, because t₂g³ has no degeneracy. --- ### (ii) **[Cu(H₂O)₆]²⁺** - **Cu oxidation state:** H₂O is neutral, so Cu = +2 - **Cu²⁺ configuration:** Atomic: [Ar] 3d¹⁰ 4s¹ Remove 2 electrons → [Ar] 3d⁹ - **H₂O is a weak field ligand:** High-spin complex, but with d⁹ configuration. - **Electronic configuration in octahedral field:** 6 electrons fill t₂g, 3 electrons in e_g (t₂g⁶ e_g³) e_g orbitals: (d_z² and d_x²−y²) → one is doubly occupied, one is singly occupied → degeneracy. - **Jahn-Teller distortion?** **YES**, classic case! d⁹ complexes almost always show strong Jahn-Teller distortion, typically elongation along one axis. --- ## **Step 3: Final Answer** ### **Conclusion** - **[Cu(H₂O)₆]²⁺** is expected to show Jahn-Teller distortion due to its d⁹ configuration, which leads to degeneracy in the e_g orbitals of the octahedral field. - **[Cr(CN)₆]³⁻** will not show Jahn-Teller distortion because its d³ configuration fills only the t₂g orbitals, which are non-degenerate. --- ## **Final Answer (with Brief Explanation)** > **[Cu(H₂O)₆]²⁺** is expected to show Jahn-Teller distortion because it has a d⁹ electronic configuration, resulting in degeneracy in the e_g orbitals of the octahedral crystal field. The complex distorts to remove this degeneracy and lower its energy. In contrast, **[Cr(CN)₆]³⁻** has a d³ configuration (t₂g³), which is non-degenerate, so it does not exhibit Jahn-Teller distortion.