Amongst $\mathrm{FeCl}_{3}.3\mathrm{H}_{2}\mathrm{O}$, $\mathrm{K}_{3}[\mathrm{Fe}(\mathrm{CN})_{6}]$ and $[\mathrm{Co}(\mathrm{NH}_{3})_{6}]\mathrm{Cl}_{3}$, the spin-only magnetic moment value of the inner-orbital complex that absorbs light at shortest wavelength is ______ B.M. [nearest integer]

JEE Main · 2022 · 25 Jun 2022 · Shift 2 · Coordination Compounds

Amongst

FeCl_{3} .3 H_{2} O

K_{3} [Fe (CN)_{6}]

and

[Co (NH_{3})_{6}] Cl_{3}

, the spin-only magnetic moment value of the inner-orbital complex that absorbs light at shortest wavelength is ______ B.M.
[nearest integer]

Answer: 2

Solution

Among the given complexes,

K_{3} [Fe (CN)_{6}]

and

[Co (NH_{3})_{6}] Cl_{3}

are inner-orbital (low-spin) complexes. Since

CN^{-}

is a stronger field ligand than

NH_{3}

K_{3} [Fe (CN)_{6}]

has larger crystal field splitting (

Δ_{0}

) and thus absorbs light at shorter wavelength.

For

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

Fe^{3 +}

d^{5}

with strong field

CN^{-}

ligands, giving

t_{2 g}^{5}

configuration with 1 unpaired electron.

Spin-only magnetic moment:

μ = n (n + 2) = 1 (3) = 1.732

B.M.

\approx

2 B.M.

JEE Main · 2022 · 25 Jun 2022 · Shift 2 · Integer answer

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