Question

\([Cr(NH_3)_6]^{3+}\) is paramagnetic while \([Ni(CN)_4]^{2+}\) is diamagnetic. Explain on the basis of valence bond theory.

Hint:

Ligand strength affects electron pairing, influencing magnetic properties of complexes.

Answer 1

Step 1: Electronic Configuration:

• Cr³⁺: 3d³, unpaired electrons → Paramagnetic
• Ni²⁺: 3d⁸, paired electrons due to strong ligand effect → Diamagnetic

Step 2: Explanation:

• NH₃ is a weak field ligand, so Cr³⁺ retains unpaired electrons.
• CN^- is a strong field ligand, causing pairing in Ni²⁺.