Which of the following complex has minimum magnitude of `Delta^(0)` ?

Options

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

Answer

C

Explanation

`[Cr(CN)_(6)]^(3-)`
`Cr^(3+)=d^(3)=t_(2g)^(3)` CFSE =-`1.2 Delta_(0)`
`[Co(NH_(3))_(6)]^(3+)` (`NH_(3)rarr` Strong field ligand)
`Co^(3+)=d^(6)=t_(2g)^(6) e_(g)^(0)` CFSE `=-2.4 Delta_(0)`
`[CoCl_(6)]^(3-)` (`Cl^(-)rarr` weak field ligand)
`Co^(3+)=d^(6)=t_(2g)^(4)e_(g)^(2)` CFSE `=-0.4 Delta_(0)`
`[Cr(H_(2)O)_(6)]^(3+) " "Cr^(3+)=d^(3)=t_(2g)^(3)e_(g)^(0)=-1.2 Delta_(0)`
Hence, minimum CFSE is for `[CoCl_(6)]^(3-)`