Question

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

• A. \( [Zn(H_2O)_6]^{2+} \)
• B. \( [Co(H_2O)_6]^{2+} \)
• C. \( [Co(en)_3]^{3+} \)
• D. \( [Ni(H_2O)_6]^{2+} \)

Hint:

Magnetic properties depend on the number of unpaired electrons. The higher the unpaired electrons, the stronger the attraction to a magnetic field.

Answer 1

The Correct Option is B

Step 1: Understanding Magnetic Properties
Paramagnetic complexes have unpaired electrons.
The more unpaired electrons, the stronger the attraction to a magnetic field.
Step 2: Compare Electron Configurations
\( Zn^{2+} \) (\( d^{10} \)) → 0 unpaired electrons (diamagnetic).
\( Co^{2+} \) (\( d^7 \)) → 3 unpaired electrons (paramagnetic).
\( Co^{3+} \) (\( d^6 \), low spin) → 0 unpaired electrons (diamagnetic).
\( Ni^{2+} \) (\( d^8 \)) → 2 unpaired electrons (paramagnetic, but weaker than \( Co^{2+} \)).
Final Answer: \( [Co(H_2O)_6]^{2+} \) has the highest paramagnetism due to 3 unpaired electrons.

Answer 2

The complex \( [Co(H_2O)_6]^{2+} \) will exhibit the maximum attraction to an applied magnetic field.

This is because \( [Co(H_2O)_6]^{2+} \) is a high-spin octahedral complex of cobalt(II), where the presence of weak field ligands like water leads to unpaired electrons.

Unpaired electrons generate a magnetic moment, causing the complex to be paramagnetic and strongly attracted to a magnetic field.

Other complexes with stronger field ligands may pair up electrons, reducing the number of unpaired electrons and hence lowering magnetic attraction.

Therefore, among common cobalt complexes, \( [Co(H_2O)_6]^{2+} \) shows maximum paramagnetism and thus the highest magnetic attraction.