Question

The reaction of \(NiBr_2\) with two equivalents of \(PPh_3\) in \(CS_2\) at -78°C gives a red-colored diamagnetic complex, \([NiBr_2 \text{(PPh}_3\text{)}_2]\). 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:

• A. tetrahedral and 1
• B. tetrahedral and 2
• C. square planar and 2
• D. square planar and 4

Hint:

For coordination complexes, the geometry changes based on temperature, and the number of unpaired electrons can be deduced based on the metal's d-electron configuration.

Answer 1

The Correct Option is B

The red-colored diamagnetic complex has a square planar geometry, but the transformation to a green-colored paramagnetic complex at 25°C suggests that the geometry is now tetrahedral. Nickel (Ni) in the tetrahedral geometry will have two unpaired electrons, making it paramagnetic.

Step 1: Consider the geometry of the complex.
At -78°C, the complex is diamagnetic and square planar, but at 25°C, the complex becomes tetrahedral and paramagnetic.

Step 2: Determine the number of unpaired electrons.
Ni has a d^8 configuration in the tetrahedral geometry, and with two unpaired electrons, the complex is paramagnetic.

Final Answer: (B) tetrahedral and 2