QJEEM21Chfba8: JEE Main 2021 Chemistry - Class 12 JEEM21Chfba8 Solution: The spin-only magnetic moment value for the complex [Co(CN) 6 ] …

[Co(CN)₆]^{4 $-$}

x + 6 $\times$ ( $-$ 1) = $-$ 4

where, x, 6, $-$ 1 and $-$ 4 are the oxidation number of Co, number of CN ligands, charge on one CN and charge on complex.

x = +2, i.e. Co²⁺

Electronic configuration of Co²⁺ : [Ar]3d⁷ and CN ^$-$ is a strong field ligand which can pair electron of central atom.


It has one unpaired electron (n) in 4d-subshell.

So, spin only magnetic moment ( $\mu$ ) = $\sqrt {n(n + 2)}$ BM = $\sqrt {1(1 + 2)}$ BM = $\sqrt 3$ BM

where, n = number of unpaired electrons

$\mu$ = $\sqrt 3$ BM = 1.73 BM

Nearest integer = 2