![Q.No.12 The coordination complex which has a distorted octahedral structure is (Given: Atomic numbers V: 23, Mn: 25, Ni: 28, Cu: 29) (a) [Ni(H2O)6]2+ (b) [Mn(H2O)6]2+ (c) [V(H2O)6]2+ (d) [Cu(H2O)6]2+](https://www.letstalkacademy.com/wp-content/uploads/2026/01/slide_12.png)
Q.No.12 The coordination complex which has a distorted octahedral structure is
(Given: Atomic numbers V: 23, Mn: 25, Ni: 28, Cu: 29)
The coordination complex with a distorted octahedral structure is [Cu(H₂O)₆]²⁺. This distortion arises due to the Jahn-Teller effect in its d⁹ configuration. Option (d) is correct.
Option Analysis
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[Ni(H₂O)₆]²⁺ (d⁸): Ni²⁺ (atomic number 28) has a high-spin d⁸ configuration with water ligands, resulting in symmetric t₂g⁶ e_g² splitting. It adopts a regular octahedral geometry.
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[Mn(H₂O)₆]²⁺ (d⁵): Mn²⁺ (atomic number 25) is high-spin d⁵ (t₂g³ e_g²), with evenly distributed electrons in degenerate orbitals. No significant Jahn-Teller distortion occurs, maintaining octahedral structure.
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[V(H₂O)₆]²⁺ (d³): V²⁺ (atomic number 23) has d³ configuration (t₂g³), where t₂g orbitals are symmetrically filled per Hund’s rule. It shows no Jahn-Teller distortion and remains octahedral.
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[Cu(H₂O)₆]²⁺ (d⁹): Cu²⁺ (d⁹, t₂g⁶ e_g³) has uneven e_g occupancy (one orbital doubly occupied, one singly), causing strong tetragonal elongation via Jahn-Teller effect for energy stabilization.
The distorted octahedral structure in coordination complexes like [Cu(H₂O)₆]²⁺ captivates students preparing for CSIR NET Life Sciences, revealing how electron configurations dictate geometry. Jahn-Teller distortion transforms ideal octahedrons into elongated forms, especially in d⁹ systems.
Jahn-Teller Effect Basics
Non-linear molecules with degenerate orbitals and uneven electron filling distort to lower symmetry and energy. Octahedral d⁹ complexes like Cu²⁺ (t₂g⁶ e_g³) elongate axially, with longer Cu-O bonds (~2.4 Å) versus equatorial (~1.96 Å).
Geometry Comparison
| Complex | d Count | Configuration (High-Spin) | Geometry |
|---|---|---|---|
| [Ni(H₂O)₆]²⁺ | d⁸ | t₂g⁶ e_g² | Regular octahedral |
| [Mn(H₂O)₆]²⁺ | d⁵ | t₂g³ e_g² | Regular octahedral |
| [V(H₂O)₆]²⁺ | d³ | t₂g³ | Regular octahedral |
| [Cu(H₂O)₆]²⁺ | d⁹ | t₂g⁶ e_g³ | Distorted octahedral |
Water, a weak-field ligand, ensures high-spin states without pairing distortions.
CSIR NET Relevance
These hexaaqua ions test crystal field theory application. Recognize d⁹ for maximum distortion among options, as symmetric fillings (d³, d⁵, d⁸) preserve octahedrons.
