Question

For an octahedral complex, which of the following d-electron configuration will give maximum CFSE?

• A. $\underset{-0.4{\Delta }_o}{\text{High spin}{d}^6}$
• B. $\underset{-1.6{\Delta }_o}{\text{Low spin}{d}^4}$
• C. $\underset{-2.0{\Delta }_o}{\text{Low spin}{d}^5}$
• D. $\underset{-0.8{\Delta }_o}{\text{High spin}{d}^7}$

Answer 1

The correct option is C $\underset{-2.0{\Delta }_o}{\text{Low spin}{d}^5}$

Low spin $d^5$ electronic configuration corresponds to $t_{2g}^5{e}_g^0$
Its CFSE is $5(-0.4{\Delta }_o)+0\left(0.6{\Delta }_o\right)=-2.0{\Delta }_o$
Thus maximum value of CFSE will be for $\underset{}{\text{Low spin}{d}^5}$ electron configuration.