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  4. The spin-only magnetic moments of [Mg(CN)6]2- and [MnBr4]2- in Bohr magnetons, respectively are

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Q. The spin-only magnetic moments of $[Mg(CN)_6]^{2-}$ and $[MnBr_4]^{2-}$ in Bohr magnetons, respectively are

KVPYKVPY 2011Coordination Compounds

Solution:

The oxidation state for $Mn$ in $Mn[(CN)_6]^{2-}$ is $+4$. The electronic
configuration for $Mn^{4+}$ is $[Ar]3d^3$.
image
As $CN^{-}$ is a strong field ligand, pairing of electrons occur
image
In case of $[Mn(CN)_6]^{2-}$
$n = 1$
$\therefore \mu=\sqrt{1\left(1+2\right)}=\sqrt{3}=1.73\,BM$
The oxidation state of $Mn$ in $[Mn Br_4]^{2-}$ is $+2$ .
The electronic configuration for $Mn^{2+}$ is $[Ar]3d^5 4s^0$.
image
As $Br^{-}$ is a weak field ligand, therefore pairing of electrons will not occur.
In this case,
$n = 5$
$\therefore \mu=\sqrt{5\left(5+2\right)}$
$=\sqrt{35}=5.92BM$