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GATE 2022 CY – Question 44

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. · 2 marks · Multiple choice

The number of S=O stretching bands in the IR spectrum of high-spin $[Mn(dmso)_6]^{3+}$ (dmso: dimethylsulfoxide) is ______.

  1. only one
  2. two with intensity ratio 1:2
  3. two with intensity ratio 1:1
  4. six with intensity ratio 1:1:1:1:1:1

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Correct answer: (B) two with intensity ratio 1:2

Explanation

Mn(III) is high-spin d4 with an orbitally degenerate ground state, so Jahn–Teller distortion splits axial and equatorial Mn–O environments. Two axial and four equatorial DMSO ligands therefore give two S=O stretching groups with relative population/intensity 1:2. **Answer: B** under the stated idealized band-intensity interpretation.