Question

Magnetic moment of $\left[Ni\right(CN{)}_4{]}^{2-}$ is zero but that of $\left[Ni\right(H_{2}O{)}_4{]}^{2+}$ is 2..83 BM.
It is because of :

• A. Didderent oxidation state of Ni in two copmlexes
• B. $C{N}^{-}$ is a strong ligand making two unpaired electron is $N{i}^{2+}$ paired while in $\left[Ni\right(H_{2}O{)}_4{]}^{2+}$, two electrons remain unpaired $H_{2}O$ being weak ligand
• C. both (a) and (b)
• D. none of the above

Answer 1

Answer: (B)

$C{N}^{-}$ is a strong ligand making two unpaired electron is $N{i}^{2+}$ paired while in $\left[Ni\right(H_{2}O{)}_4{]}^{2+}$, two electrons remain unpaired $H_{2}O$ being weak ligand

$N{i}^{+2}{d}^8$ configuration
In presence of $C{N}^{-}$ (strong ligand) pairing of electrons happens and low spin complex forms but in presence of aqua, pairing doesnt happen and high spin complex forms so magnetic moment of $\left[Ni\right(CN{)}_4{]}^{2-}$ is zero but that of $\left[Ni\right(H_{2}O{)}_4{]}^{2+}$ is 2..83 BM.