Question

In which of the following complex ions will the metal ion have $t_{2g}^6{e}_g^0$ configuration according to CFT?

• A. $[Fe{F}_6{]}^{2-}$
• B. $\left[Fe\right(CN{)}_6{]}^{3-}$
• C. $\left[Fe\right(CN{)}_6{]}^{4-}$
• D. None of these

Answer 1

The correct option is C $\left[Fe\right(CN{)}_6{]}^{4-}$

For $t_{2g}^6{e}_g^0$, $Fe$ should contain 6 electrons in its valence shell. So we can eliminate option (b) since here Fe is in +3 oxidation state. Again, in the given configuration all the electrons are paired so the ligand must be strong field. Hence in $\left[Fe\right(CN{)}_6{]}^{4-}$ the metal is in $t_{2g}^6{e}_g^0$ configuration.