Coordination Compounds 2 Question 11

####12. The pair of metal ions that can given a spin-only magnetic moment of $3.9 BM$ for the complex $\left[M\left(H _2 O\right) _6\right] Cl _2$, is

(a) $Co^{2+}$ and $Fe^{2+}$

(b) $Cr^{2+}$ and $Mn^{2+}$

(c) $V^{2+}$ and $Co^{2+}$

(d) $V^{2+}$ and $Fe^{2+}$

(2019 Main, 12 Jan I)

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Solution:

  1. As $H _2 O$ is a weak field ligand. It readily forms high spin complexes. $\operatorname{In}\left[M\left(H _2 O\right) _6\right] Cl _2, M$ exist in +2 oxidation state. The arrangement of electrons in the given metal ions are as follows:
Metal
ions
Configuration Number of
unpaired
electrons
Spin only
Magnetic
moment (in
BM) $=\sqrt{\boldsymbol{n}(\boldsymbol{n}+\mathbf{2})}$
$Co^{2+}$ $\left(d^{7}\right)=t _{2 g}^{5} e _g^{2}$ 3 3.9
$Fe^{2+}$ $\left(d^{6}\right)=t _{2 g}^{4} e _g^{2}$ 4 4.9
$Cr^{2+}$ $\left(d^{4}\right)=t _{2 g}^{3} e _g^{1}$ 4 4.9
$Mn^{2+}$ $\left(d^{5}\right)=t _{2 g}^{3} e _g^{2}$ 5 5.9
$V^{2+}$ $\left(d^{3}\right)=t _{2 g}^{3} e _g^{0}$ 3 3.9

Therefore, $Co^{2+}$ and $V^{2+}$ contains same value of magnetic moment (3.9 BM).



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