In which of the following coordination entities the magnitude of `Deltao` (CFSE in ocetahedral field) will be maximum?

Options

A. `[Co(H_(2)O)_(6)]^(3+)`
B. `[Co(NH_(3))_(6)]^(3+)`
C. `[Co(CN)_(6)]^(3-)`
D. `[Co(C_(2)O_(4))_(3)]^(3-)`

Answer

C

Explanation

The magnitude of `D_("cot")` (the orbital spitting energy) is decided by the nature of ligand. Strong field ligand has highest `D_("cot")`. The increasing field strength is as
`I^(-) lt Br^(-) lt Cl^(-) lt F^(-) lt OH^(-) lt H_(2)O lt C_(2)O_(4)^(2-) lt NH_(3) lt en NO_(2)^(-) lt CN^(-)`
The `CN^(-)` is the strongest ligand among these, hence the magnitude of `D_("oct")` will be maximum in `[Co(CN)_(6)]^(3-)`.