The magnetic moment is measured in Bohr Magneton (BM). Spin only magnetic moment of Fe in $\left[\mathrm{Fe}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{3+}$ and $\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]^{3-}$ complexes respectively is :

JEE Main · 2023 · 11 Apr 2023 · Shift 2 · Coordination Compounds

The magnetic moment is measured in Bohr Magneton (BM).
Spin only magnetic moment of Fe in

[Fe (H_{2} O)_{6}]^{3 +}

and

[Fe (CN)_{6}]^{3 -}

complexes respectively is :

(A)6.92 B.M. in both
(B)4.89 B.M. and 6.92 B.M.
(C)3.87 B.M. and 1.732 B.M.
(D)5.92 B.M. and 1.732 B.M✓ Correct

Answer: (D)

Solution

For

[Fe (H_{2} O)_{6}]^{3 +}

: Fe³⁺ has configuration [Ar]3d⁵. H₂O is a weak field ligand, so no pairing occurs. Number of unpaired electrons = 5. Magnetic moment

μ = n (n + 2) = 5 (7) = 35 \approx 5.92

B.M.

For

[Fe (CN)_{6}]^{3 -}

: CN⁻ is a strong field ligand, causing pairing. The 5 electrons pair up leaving 1 unpaired electron. Magnetic moment

μ = 1 (3) = 3 \approx 1.732

B.M.

JEE Main · 2023 · 11 Apr 2023 · Shift 2 · Single correct option

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