Question

Which of the following complexes will exhibit maximum attraction to an applied magnetic field?

• A. [Co(en)₃]³⁺
• B. [Co(H₂O)₆]²⁺
• C. [Zn(H₂O)₆]²⁺
• D. [Ni(H₂O₆]²⁺

Answer 1

The Correct Option is B

The attraction of a complex to a magnetic field depends on the number of unpaired electrons in the complex. Let us analyze each given complex: 

1.[Zn(H\(_2\)O)\(_6\)]\(^{2+}\): The electronic configuration of Zn\(^{2+}\) is \( 3d^{10} \). It has no unpaired electrons, so it is diamagnetic. 

2. [Ni(H\(_2\)O)\(_6\)]\(^{2+}\): The electronic configuration of Ni\(^{2+}\) is \( 3d^8 \). In an octahedral field, this gives a \( t_{2g}^6 e_g^2 \) configuration, with 2 unpaired electrons. 

3. [Co(en)\(_3\)]\(^{3+}\): The electronic configuration of Co\(^{3+}\) is \( 3d^6 \). Due to strong-field ligands (en), it undergoes pairing, resulting in a \( t_{2g}^6 e_g^0 \) configuration with no unpaired electrons. It is diamagnetic. 

4. [Co(H\(_2\)O)\(_6\)]\(^{2+}\): The electronic configuration of Co\(^{2+}\) is \( 3d^7 \). In an octahedral field with weak-field ligands like water, it gives a \( t_{2g}^5 e_g^2 \) configuration with 3 unpaired electrons. Hence, [Co(H\(_2\)O)\(_6\)]\(^{2+}\) has the maximum number of unpaired electrons and will exhibit the maximum attraction to an applied magnetic field.