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Indian Forest Service (Mains)

Chemistry optional

  • 2 papers
  • 200 marks each
  • 3 h per paper

Paper I covers physical and inorganic chemistry.

Indian Forest Service (Mains), Chemistry optional · 2024 · Paper I

Q5(c). Dicobalt octacarbonyl and infrared bands

Question

Predict the structure of Co(CO)8 with the help of 18-electron rule. What differences do you expect in C–O stretching frequency(ies) between Co(CO)8 and Mn(CO)10? Explain. Atomic numbers: Mn = 25; Co = 27. [Formulas printed as in the paper; the intended compounds are Co₂(CO)₈ and Mn₂(CO)₁₀.]

Answer in brief

The intended compounds are Co₂(CO)₈ and Mn₂(CO)₁₀. Bridged dicobalt octacarbonyl has six terminal and two bridging CO ligands plus a Co–Co bond; the bridges give lower-frequency C–O bands.

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Topic notes: metal carbonyls, nitrosyls, the 18-electron and EAN rules, metal–metal bonds and clusters, with every Civil Services, IFoS and Geo-Scientist PYQ →

Coversdicobalt octacarbonyl18-electron rulebridging carbonylIR C–O stretching frequencyMn2(CO)10

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