Write IUPAC name of the complex `[Cr(NH_(3))_(4)Cl_(2)]Cl.` What type of isomerism is exhibited by the complex `[Co(en)_(3)]^(3+)` (en = ethane - 1, 2 - diamine) ? Why is `[NiCl_(4)]^(2-)` paramagnetic but `[Ni(CO)_(4)]` is diamagnetic ? (Atomic no : Cr = 24, Co = 27, Ni = 28)

Explanation

tetraamminedichloridochromium (III) chloride , Optical isomerism
In `[NiCl_(4)]^(2-), Ni^(2+): [Ar]3d^(8)4s^(0)`

`Ni^(2+)` has two unpaired electrons, hence, `[NiCl_(4)]^(2-)` is paramagnetic in nature.
In `[Ni(CO)_(4)], Ni:[Ar]3d^(8)4s^(2)`

`CO` is a strong field ligand, hence, pairing occurs, i.e.,

Ni has no unpaired electrons, hence `[Ni(CO)_(4)]` is diamagnetic in nature.