The GATE Grind

GATE 2021 CY – Question 22

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 reaction of NiBr2 with two equivalents of PPh3 in CS2 at –78 °C gives a red-colored diamagnetic complex, [NiBr2(PPh3)2]. This transforms to a green-colored paramagnetic complex with the same molecular formula at 25 °C. The geometry and the number of unpaired electrons in the green-colored complex, respectively, are:

  1. tetrahedral and 1
  2. tetrahedral and 2
  3. square planar and 2
  4. square planar and 4

Practise this question in The GATE Grind →

Show answer and explanation

Correct answer: (B) tetrahedral and 2

Explanation

Ni(II) is d8. The red diamagnetic form is square planar, with all electrons paired. The green paramagnetic form is tetrahedral: the tetrahedral d8 arrangement is e4t2⁴, leaving two electrons unpaired in the upper t2 set.

Hence **tetrahedral with two unpaired electrons, B**.