Question

Amongst $Ni(CO)_4, [Ni(CN)_4]^{2-} $ and $ NiCl_4^{2-}$

• A. $Ni(CO)_4 $ and $ NiCl_4^{2-}$ are diamagnetic and $[Ni(CN)_4]^{2-}$ is paramagnetic
• B. $[NiCl_4]^{2-}$ and $[Ni(CN)_4]^{2-}$ are diamagnetic and $Ni(CO)_4$ is paramagnetic
• C. $Ni(CO)_4$ and $[Ni(CN)_4]^{2-}$ are diamagnetic and $[NiCl_4]^{2-}$ is paramagnetic
• D. $Ni(CO)_4 $ is diamagnetic and $[NiCl_4]^{2-} $ and $ [Ni(CN)_4]^{2-} $ are paramagnetic

Answer 1

Answer: (C)

In $Ni(CO)_4, Ni$ has $3d^{10} $ -configuration, diamagnetic. In $Ni(CN)_4]^{2-}, Ni $ has $3d^8 $ -configuration but due to strong ligand field, all the ($d$-electrons are spin paired giving $dsp^2 $ -hybridisation diamagnetic.
In $[NiCl_4]^{2-} , Ni$ has $3d^8 $ -configuration and there is two unpaired electrons (weak chloride ligand do not pair up $d$ - electrons), hence paramagnetic.