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:
- 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).
