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GATE 2023 CY – Question 25

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 choice

The magnitudes of CFSE in $[M(H_2O)_6]^{n+}$ for Mn and Fe satisfy ______.

  1. $Mn^{2+}<Mn^{3+}$ and $Fe^{2+}<Fe^{3+}$
  2. $Mn^{2+}>Mn^{3+}$ and $Fe^{2+}>Fe^{3+}$
  3. $Mn^{2+}<Mn^{3+}$ and $Fe^{2+}>Fe^{3+}$
  4. $Mn^{2+}>Mn^{3+}$ and $Fe^{2+}<Fe^{3+}$

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Correct answer: (C) $Mn^{2+}<Mn^{3+}$ and $Fe^{2+}>Fe^{3+}$

Explanation

Water gives high-spin octahedral ions. Mn2+(d5) hasCFSE0 whileMn3+(d4) has 0.6Δo; Fe2+(d6) has 0.4Δo whileFe3+(d5) has 0.

Thus **Mn2+<Mn3+ and Fe2+>Fe3+, C**. The zero values follow equal occupation of the five d orbitals.