Question

The number of paramagnetic species from the following is ________
$ {\left[ Ni ( CN )_4\right]^{2-} \cdot\left[ Ni ( CO )_4\right],\left[ NiCl _4\right]^{2-}} $ $ {\left[ Fe ( CN )_6\right]^{4-},\left[ Cu \left( NH _3\right)_4\right]^{2+}}$ $ {\left[ Fe ( CN )_6\right]^{3-} \text { and }\left[ Fe \left( H _2 O \right)_6\right]^{2+}}$

Answer 1

Correct Answer: 4

To determine the number of paramagnetic species, we must assess each compound's electronic configuration to check for unpaired electrons, which cause paramagnetism.

1. ${\left[ Ni ( CN )_4\right]^{2-}}$: Ni has an oxidation state of +2. In this complex, $CN^-$ is a strong field ligand causing $Ni^{2+}$ to have an electronic configuration of $d^8$ in a square planar geometry, leading to paired electrons. Thus, it is not paramagnetic.
2. ${\left[ Ni ( CO )_4\right]}$: Ni in $Ni^0$ state with CO as a strong field ligand. This complex has a $d^{10}$ configuration with no unpaired electrons, making it not paramagnetic.
3. ${\left[ NiCl_4\right]^{2-}}$: Cl⁻ is a weak field ligand, causing $Ni^{2+}$ to have a $d^8$ configuration in tetrahedral geometry, retaining 2 unpaired electrons. Thus, it is paramagnetic.
4. ${\left[ Fe ( CN )_6\right]^{4-}}$: $Fe^{2+}$ in high spin state with a strong field ligand. It has a $t_{2g}^{6}e_g^0$ configuration with paired electrons. Therefore, it is not paramagnetic.
5. ${\left[ Cu ( NH_3 )_4\right]^{2+}}$: Cu in $Cu^{2+}$ state has $d^9$ configuration with one unpaired electron. This makes it paramagnetic.
6. ${\left[ Fe ( CN )_6\right]^{3-}}$: $Fe^{3+}$ with strong field ligand leads to $t_{2g}^{5}e_g^0$, having one unpaired electron. Hence, it is paramagnetic.
7. ${\left[ Fe ( H_2O )_6\right]^{2+}}$: $Fe^{2+}$ in high spin octahedral field has $d^6$ configuration, thus containing 4 unpaired electrons. It is paramagnetic.

Concluding, there are 4 paramagnetic species: ${\left[ NiCl_4\right]^{2-}}, {\left[ Cu \left( NH _3\right)_4\right]^{2+}}, {\left[ Fe ( CN )_6\right]^{3-}}, \text{ and } {\left[ Fe \left( H _2 O \right)_6\right]^{2+}}$. The solution of 4 is within the given range (4,4).