Question

Which one of the following has a square planar geometry?
`(Co=27, Ni=28, Fe=26, Pt=78)`
A. `[CoCl_(4)]^(2-)`
B. `[FeCl_(4)]^(2-)`
C. `[NiCl_(4)]^(2-)`
D. `[PtCl_(4)]^(2-)`

Answer 1

Correct Answer - D
`._(27)Co^(2+)-1s^(2)2s^(2)2p^(6)3s^(2)3p^(6)3d^(7)4s^(0)`

As`Cl^(-)` is weak field ligand so no pairing up .
Hence, it is `sp^(3)` hybridized givigng tetrahedral geometry.
`Fe^(2+)-1s^(2)2s^(2)2p^(6)3s^(2)3p^(6)3d^(6)4s^(0)`

Due to `Cl^(-)` , back pairig is not observed so it will be `sp^(3)` hybridized giving tetrahedral geometry.
`Ni^(2+)-1s^(2)2s^(2)2p^(6)3s^(2)3p^(6)3d^(6)4s^(0)`

Because of weak ligand, back pairing is not observed so it will be `sp^(3)` i.e., tetrahedral geometry.
All the complexes of `Pt^(2+)` are square planar including those with weak field ligand such as halide ions thus (d) is correct.