Question

The CFSE for a $d^7$ system with a strong field ligand will be (in ${\Delta }_o$ units):

• A. $-1.6{\Delta }_o$
• B. $+1.8{\Delta }_o$
• C. $-1.8{\Delta }_o$
• D. $+1.6{\Delta }_o$

Answer 1

The correct option is C $-1.8{\Delta }_o$

In a strong field, the 'd' electrons tend towards maximum pairing.
So, 6 electrons are there in $t_{2g}$ and 1 electron is present in $e_g$ orbital.
Hence, the CFSE would be $(-6\times 0.4+1\times 0.6)=-1.8{\Delta }_o$.