Question

How many of the following do not have square planar geometry ?
$\left[FeCl_{4}\right]^{2 -},\left[NiCl_{4}\right]^{2 -},\left[PtCl_{4}\right]^{2 -},\left[CoCl_{4}\right]^{2 -}$

Answer 1

$\left(\left[Fe \left(Cl\right)_{4}\right]\right)^{2 -}$ has $Fe^{+ 2}$ oxidation number with $\left[Ar\right]3d^{6}$ electronic configuration and as $Cl^{-}$ is weak field ligand hence its geometry will be tetrahedral with $sp^{3}$ hybridisation.
. $\left(\left[Ni \left(Cl\right)_{4}\right]\right)^{2 -}$ has $Ni^{+ 2}$ oxidation number with $\left[Ar\right]3d^{8}$ electronic configuration and as $Cl^{-}$ is weak field ligand hence its geometry will be tetrahedral with $sp^{3}$ hyridisation.
$\left(\left[Co \left(Cl\right)_{4}\right]\right)^{2 -}$ has $Co^{+ 2}$ oxidation number with $\left[Ar\right]3d^{7}$ electronic configuration and as $Cl^{-}$ is weak field ligand hence its geometry will be tetrahedral with $sp^{3}$ hybridisation.
While exceptionally $\left[PtCl_{4}\right]^{2 -}$ has square planar structure with $dsp^{2}$ hybridisation.