Question

Which of the following are paramagnetic?
A. [NiCl$_4$]$^{2-}$
B. Ni(CO)$_4$
C. [Ni(CN)$_4$]$^{2-}$
D. [Ni(H$_2$O)$_6$]$^{2+}$
E. Ni(PPh$_3$)$_4$
Choose the correct answer from the options given below:

• A. B and E only
• B. A and D only
• C. A, D, and E only
• D. A and C only

Hint:

Paramagnetism is caused by the presence of unpaired electrons. Strong field ligands (such as CO, CN\(^-\)) cause pairing of electrons and lead to diamagnetism, while weak field ligands (such as water and PPh\(_3\)) do not cause electron pairing, leading to paramagnetism.

Answer 1

The Correct Option is C

To ascertain paramagnetism, the presence of unpaired electrons in the complex must be confirmed. Paramagnetic substances possess unpaired electrons, whereas diamagnetic substances have all electrons paired.

1. [NiCl\(_4\)]\(^{2-}\): Ni\(^2+\) has an electronic configuration of [Ar] 3d\(^8\). Within a tetrahedral field, characteristic of this complex, the Ni\(^2+\) ion exhibits unpaired electrons, rendering [NiCl\(_4\)]\(^{2-}\) paramagnetic.

2. Ni(CO)\(_4\): Carbon monoxide (CO) acts as a strong field ligand, inducing electron pairing in Ni, resulting in a diamagnetic complex. Consequently, Ni(CO)\(_4\) is diamagnetic.

3. [Ni(CN)\(_4\)]\(^{2-}\): The cyanide ion (CN\(^-\)) is a very strong field ligand, causing the pairing of electrons in Ni\(^2+\).
Therefore, [Ni(CN)\(_4\)]\(^{2-}\) is diamagnetic.

4. [Ni(H\(_2\)O)\(_6\)]\(^{2+}\): Water (H\(_2\)O) functions as a weak field ligand. In a weak field ligand environment, Ni\(^2+\) (d\(^8\)) retains unpaired electrons, making [Ni(H\(_2\(_2\)O)\(_6\)]\(^{2+}\) paramagnetic.

5. Ni(PPh\(_3\))\(_4\): Triphenylphosphine (PPh\(_3\)) is a weak field ligand. In this environment, Ni\(^2+\) will possess unpaired electrons, classifying Ni(PPh\(_3\))\(_4\) as paramagnetic.


Accordingly, the correct designation is (3) A, D, and E only.