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 determine paramagnetism, we must check if the complex has unpaired electrons. A paramagnetic substance has unpaired electrons, while a diamagnetic substance has all electrons paired.
1. [NiCl\(_4\)]\(^{2-}\): Ni\(^2+\) has an electronic configuration of [Ar] 3d\(^8\). In a tetrahedral field like in this complex, the Ni\(^2+\) ion has unpaired electrons, and thus [NiCl\(_4\)]\(^{2-}\) is paramagnetic.
2. Ni(CO)\(_4\): CO is a strong field ligand that causes pairing of the electrons in Ni, leading to a diamagnetic complex. Hence, Ni(CO)\(_4\) is diamagnetic.
3. [Ni(CN)\(_4\)]\(^{2-}\): CN\(^-\) is a very strong field ligand, and it causes pairing of electrons in Ni\(^2+\).
Therefore, [Ni(CN)\(_4\)]\(^{2-}\) is diamagnetic.
4. [Ni(H\(_2\)O)\(_6\)]\(^{2+}\): Water is a weak field ligand, and Ni\(^2+\) (d\(^8\)) has unpaired electrons in a weak field ligand environment, making [Ni(H\(_2\)O)\(_6\)]\(^{2+}\) paramagnetic.
5. Ni(PPh\(_3\))\(_4\): PPh\(_3\) is a weak field ligand, and Ni\(^2+\) in this environment will have unpaired electrons, making Ni(PPh\(_3\))\(_4\) paramagnetic.

Thus, the correct answer is (3) A, D and E only.