Consider the following nickel complexes:

A = [Ni(CN)₄]²⁻

B = [Ni(CO)₄

C = [NiCl₄]²⁻

Which option correctly describes their magnetic behaviour?

Solution:

Nickel atomic number = 28

Ni:

[Ar] 3d⁸ 4s²

For A:

[Ni(CN)₄]²⁻

Ni²⁺ = 3d⁸

CN⁻ is a strong field ligand.

Electron pairing occurs.

Square planar structure forms.

All electrons are paired.

A is diamagnetic.

For B:

[Ni(CO)₄

CO is a strong field ligand.

Nickel is in oxidation state zero.

Configuration becomes effectively paired.

B is diamagnetic.

For C:

[NiCl₄]²⁻

Cl⁻ is a weak field ligand.

Tetrahedral geometry forms.

Two unpaired electrons remain.

C is paramagnetic.

Answer:

A and B are diamagnetic; C is paramagnetic (Option 1)