GATE 2024 CY – Question 21

Inorganic Chemistry · Transition Metals: Coordination chemistry – structure and isomerism, theories of bonding (VBT, CFT, and MOT). Metal-metal multiple bonds. Energy level diagrams in various crystal fields, CFSE, applications of CFT, Jahn-Teller distortion. Electronic spectra of transition metal complexes: spectroscopic term symbols, selection rules, Orgel and Tanabe-Sugano diagrams, nephelauxetic effect and Racah parameter, charge-transfer spectra. Magnetic properties of transition metal complexes. Ray-Dutt and Bailar twists, Reaction mechanisms: kinetic and thermodynamic stability, associative, dissociative substitution and redox reactions. · 1 mark · Multiple select

The complex(es) with distorted octahedral structure is (are)

$[\mathrm{VF_6}]^{3-}$
$[\mathrm{FeF_6}]^{3-}$
$[\mathrm{MnF_6}]^{3-}$
$[\mathrm{Fe(CN)_6}]^{4-}$

Practise this question in The GATE Grind →

Show answer and explanation

Correct answer: (A) $[\mathrm{VF_6}]^{3-}$; (C) $[\mathrm{MnF_6}]^{3-}$

Explanation

A complex shows **Jahn-Teller distortion** (a distorted octahedron) when its ground electron configuration is orbitally degenerate, i.e. when the $t_{2g}$ or $e_g$ orbitals are unevenly occupied.

**$[\text{VF}_6]^{3-}$:** V(III) is $d^2$, $t_{2g}^2$: the two electrons occupy three $t_{2g}$ orbitals unevenly, giving a degenerate ground state. Distorted. ✓
**$[\text{FeF}_6]^{3-}$:** Fe(III) is high-spin $d^5$, $t_{2g}^3e_g^2$, a symmetric configuration. Regular octahedron. ✗
**$[\text{MnF}_6]^{3-}$:** Mn(III) is high-spin $d^4$, $t_{2g}^3e_g^1$: the single $e_g$ electron is in a degenerate pair, strong Jahn-Teller distortion. ✓
**$[\text{Fe(CN)}_6]^{4-}$:** Fe(II) is low-spin $d^6$, $t_{2g}^6$, a filled set. Regular. ✗

Answer **A and C**.