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GATE 2021 CY – Question 52

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 correct order of increasing intensity (molar absorptivity) of the UV-visible absorption bands for the ions [Ti(H2O)6]3+, [Mn(H2O)6]2+, [CrO4]2–, and [NiCl4]2– is:

  1. [Ti(H2O)6]3+ < [Mn(H2O)6]2+ < [CrO4]2– < [NiCl4]2–
  2. [Mn(H2O)6]2+ < [Ti(H2O)6]3+ < [NiCl4]2– < [CrO4]2–
  3. [NiCl4]2– < [Ti(H2O)6]3+ < [Mn(H2O)6]2+ < [CrO4]2–
  4. [Ti(H2O)6]3+ < [NiCl4]2– < [CrO4]2– < [Mn(H2O)6]2+

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Correct answer: (B) [Mn(H2O)6]2+ < [Ti(H2O)6]3+ < [NiCl4]2– < [CrO4]2–

Explanation

High-spin octahedral Mn(II), d5, has spin-forbidden as well as Laporte-forbidden d–d bands and is weakest. Octahedral Ti(III) has spin-allowed but Laporte-forbidden d–d absorption. Tetrahedral NiCl4²− lacks inversion symmetry, making its d–d bands stronger. Chromate has intense allowed charge-transfer absorption and is strongest.

Therefore **Mn<Ti<Ni<CrO4, B**.