The complex showing a spin-only magnetic moment of $2.82 \mathrm{~B} . \mathrm{M}$. is

(B) $\left[\mathrm{NiCl}_{4}\right]^{2-}$

(A) $\mathrm{Ni}(\mathrm{CO})_{4}$

(C) $\mathrm{Ni}\left(\mathrm{PPh}_{3}\right)_{4}$

(D) $\left[\mathrm{Ni}(\mathrm{CN})_{4}\right]^{2-}$

JEE Advanced · 2010 · 11 Apr 2010 · Paper 2 · Coordination Compounds

The complex showing a spin-only magnetic moment of

2.82 B . M

. is

(A) $Ni (CO)_{4}$
(B) $[NiCl_{4}]^{2 -}$ ✓ Correct
(C) $Ni (PPh_{3})_{4}$
(D) $[Ni (CN)_{4}]^{2 -}$

Answer: (B)

Solution

A spin-only magnetic moment of 2.82 B.M. corresponds to

n = 2

unpaired electrons (

μ = n (n + 2)

[NiCl_{4}]^{2 -}

is tetrahedral with weak-field Cl⁻ ligands, so Ni²⁺ (d⁸) remains high-spin with 2 unpaired electrons. The other complexes are either diamagnetic (Ni(CO)₄, Ni(PPh₃)₄, [Ni(CN)₄]²⁻) due to strong-field ligands or square-planar geometry.

JEE Advanced · 2010 · 11 Apr 2010 · Paper 2 · Single correct option

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