Amongst $F e C l_{3} .3 H_{2} O, K_{3} [F e (C N)_{6})]$ and
$[C o (N H_{3})_{6}] C l_{3}$ , the spin-only magnetic moment value of the inner-orbital complex that absorbs light at shortest wavelength is_______B.M. [nearest integer]

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Solution

Strong field ligand forms Inner-orbital complex.
$C N^{-}$ and $N H_{3}$ are strong field ligands.
$[F e (H_{2} O)_{3} C l_{3}] \to$ Outer-orbital complex
$K_{3} [F e (C N)_{6}] \to$ Inner-orbital complex
$[C o (N H_{3})_{6}] C l_{3} \to$ Inner-orbital complex

Since $C N^{-}$ is a strong field ligand than $N H_{3}$ .
Hence $K_{3} [F e (C N)_{6}]$ is the inner-orbital complex that absorbs light at shortest wavelength.
$F e (I I I) \to$ valence shell configuration $3 d^{5}$
Since $C N^{-}$ will do pairing, so unpaired electron $= 1$

$μ = \sqrt{1 (1 + 2)} = \sqrt{3} BM \approx 2 BM$

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Similar questions

Using valence bond theory, explain the following in relation to the complexes given below
$[M n (C N)_{6}]^{3 -}, [C o (N H_{3})_{6}]^{3 +}, [C r (H_{2} O)_{6}]^{3 +}, [F e C l_{6}]^{4 -}$
(a) Type of hybridisation
(b) Inner or outer orbital
(c) Magnetic behaviour
(d) Spin only magnetic moment value.