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

1. Determine the electronic configuration and geometry for each species: 

- \([\text{Ni(CN)}_4]^{2-}: \text{Ni}^{2+} \, (3d^8) \, \text{in a strong field ligand, forms a square planar complex.} \, \text{No unpaired electrons. (Diamagnetic)}\) 
- \([\text{Ni(CO)}_4]: \text{Ni}^{0} \, (3d^8 4s^2) \, \text{in a strong field ligand, forms a tetrahedral complex.} \, \text{No unpaired electrons. (Diamagnetic)}\) 
- \([\text{NiCl}_4]^{2-}: \text{Ni}^{2+} \, (3d^8) \, \text{in a weak field ligand, forms a tetrahedral complex.} \, \text{2 unpaired electrons. (Paramagnetic)}\) 
- \([\text{Fe(CN)}_6]^{3-}: \text{Fe}^{3+} \, (3d^5) \, \text{in a strong field ligand, forms a low-spin octahedral complex.} \, \text{1 unpaired electron. (Paramagnetic)}\) 
- \([\text{Cu(NH}_3)_4]^{2+}: \text{Cu}^{2+} \, (3d^9) \, \text{1 unpaired electron. (Paramagnetic)}\) 
- \([\text{Fe(H}_2\text{O)}_6]^{2+}: \text{Fe}^{2+} \, (3d^6) \, \text{in a weak field ligand, forms a high-spin octahedral complex.} \, \text{4 unpaired electrons. (Paramagnetic)}\) 

2. Count the paramagnetic species: 

Paramagnetic species: \([\text{NiCl}_4]^{2-}, [\text{Fe(CN)}_6]^{3-}, [\text{Cu(NH}_3)_4]^{2+}, [\text{Fe(H}_2\text{O)}_6]^{2+}\). 
Total = 4 species. Thus, the number of paramagnetic species is 4. 

Paramagnetic species have unpaired electrons, determined by ligand field strength and electron configurations. Strong field ligands like CN\(^-\) and CO lead to low-spin complexes, while weak field ligands like Cl\(^-\) and H\(_2\)O result in high-spin complexes.