The GATE Grind

GATE 2019 CY – Question 36

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

Which pair of aqueous ions has measured magnetic moments close to spin-only values? Atomic numbers: Cr24, Co27, Gd64, Tb65, Dy66, Lu71.

  1. Cr(III) and Gd(III)
  2. Co(II) and Gd(III)
  3. Cr(III) and Dy(III)
  4. Lu(III) and Tb(III)

Practise this question in The GATE Grind →

Show answer and explanation

Correct answer: (A) Cr(III) and Gd(III)

Explanation

Cr³⁺ is d³ with largely quenched orbital contribution in its aqueous complex. Gd³⁺ has half-filled 4f⁷ and L=0, making its moment well approximated by spin only. Co²⁺, Tb³⁺ and Dy³⁺ have substantial orbital contributions. Therefore A; the spin-only magnitudes are approximately √15 and √63 μB respectively.

More 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. questions

All 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. questions →