Question

The correct statement among the following is:

• A. \(\mathrm{Ni(CO)_4}\) is diamagnetic and \([\mathrm{NiCl_4}]^{2-}\) and \([\mathrm{Ni(CN)_4}]^{2-}\) are paramagnetic.
• B. \(\mathrm{Ni(CO)_4}\) and \([\mathrm{NiCl_4}]^{2-}\) are diamagnetic and \([\mathrm{Ni(CN)_4}]^{2-}\) is paramagnetic.
• C. \([\mathrm{Ni(CN)_4}]^{2-}\) and \([\mathrm{NiCl_4}]^{2-}\) are diamagnetic and \(\mathrm{Ni(CO)_4}\) is paramagnetic.
• D. \(\mathrm{Ni(CO)_4}\) and \([\mathrm{Ni(CN)_4}]^{2-}\) are diamagnetic and \([\mathrm{NiCl_4}]^{2-}\) is paramagnetic.

Hint:

Strong-field ligands (CN\(^-\), CO) favour pairing and diamagnetism, while weak-field ligands (Cl\(^-\)) lead to paramagnetism.

Answer 1

The Correct Option is D

Concept: Magnetic behaviour depends on:
Oxidation state of metal
Nature of ligands (strong-field or weak-field)
Geometry of the complex
Step 1: Analyze \(\mathrm{Ni(CO)_4}\)
Oxidation state of Ni = 0
Configuration: \(3d^{10}\)
All electrons paired \[ \Rightarrow \mathrm{Ni(CO)_4} \text{ is diamagnetic} \]
Step 2: Analyze \([\mathrm{Ni(CN)_4}]^{2-}\)
Oxidation state of Ni = +2 \(\Rightarrow d^8\)
CN\(^-\) is a strong-field ligand
Square planar geometry (low spin) All electrons paired. \[ \Rightarrow [\mathrm{Ni(CN)_4}]^{2-} \text{ is diamagnetic} \]
Step 3: Analyze \([\mathrm{NiCl_4}]^{2-}\)
Oxidation state of Ni = +2 \(\Rightarrow d^8\)
Cl\(^-\) is a weak-field ligand
Tetrahedral geometry (high spin) Two unpaired electrons present. \[ \Rightarrow [\mathrm{NiCl_4}]^{2-} \text{ is paramagnetic} \] Final Answer: \[ \boxed{\text{Option (D)}} \]