JEE Advanced · 2015 · 24 May 2015 · Paper 1 · Coordination Compounds

For the octahedral complexes of

Fe^{3 +}

SCN^{-}

(thiocyanato-S) and in

CN^{-}

ligand environments, the difference between the spin-only magnetic moments in Bohr magnetons (when approximated to the nearest integer) is
[Atomic number of

Fe = 26

]

Answer: 4

Solution

Fe^{3 +}

has electronic configuration [Ar]3d⁵.

**With

SCN^{-}

(weak field ligand):** No pairing occurs, 5 unpaired electrons.

μ = n (n + 2) = 5 (7) = 35 \approx 6

BM

**With

CN^{-}

(strong field ligand):** Pairing occurs, 1 unpaired electron.

μ = 1 (3) = 3 \approx 2

BM

Difference = 6 - 2 = 4 BM.

JEE Advanced · 2015 · 24 May 2015 · Paper 1 · Integer answer

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