The calculated magnetic moments (spin only value) for species $\left[\mathrm{FeCl}_{4}\right]^{2-}$, $\left[\mathrm{Co}\left(\mathrm{C}_{2} \mathrm{O}_{4}\right)_{3}\right]^{3-}$ and $\mathrm{MnO}_{4}^{2-}$ respectively are:

JEE Main · 2021 · 24 Feb 2021 · Shift 2 · Coordination Compounds

The calculated magnetic moments (spin only value) for species

[FeCl_{4}]^{2 -}

[Co (C_{2} O_{4})_{3}]^{3 -}

and

MnO_{4}^{2 -}

respectively are:

(A) $4.90, 0$ and 1.73 BM✓ Correct
(B)5.92, 4.90 and 0 BM
(C) $4.90, 0$ and 2.83 BM
(D)5.82, 0 and 0 BM

Answer: (A)

Solution

For

[FeCl_{4}]^{2 -}

Fe^{2 +}

has

3 d^{6}

configuration.

Cl^{-}

is a weak field ligand, so no pairing occurs. With 4 unpaired electrons,

μ = 4 (4 + 2) = 4.90

BM.

For

[Co (C_{2} O_{4})_{3}]^{3 -}

Co^{3 +}

has

3 d^{6}

configuration.

C_{2} O_{4}^{2 -}

is a strong field ligand causing pairing. With 0 unpaired electrons,

μ = 0

BM.

For

MnO_{4}^{2 -}

Mn^{6 +}

has

3 d^{1}

configuration. With 1 unpaired electron,

μ = 1 (1 + 2) = 1.73

BM.

JEE Main · 2021 · 24 Feb 2021 · Shift 2 · Single correct option

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