Question

What will be the CFSE value of $d^7$ configuration of octahedral complex in presence of strong field igand?

• A. $-2.4{\Delta }_o$
• B. $-1.4{\Delta }_o$
• C. $-1.8{\Delta }_o$
• D. 0

Answer 1

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

The given configuration is $d^7$.
The given complex is a octahedral complex and the ligand is a strong field ligand. Thus, it is a low spin complex, so the pairing energy will be less than the crystal field splitting energy.

$d^7$: $t_{2g}^6{e}_g^1$
$\text{CFSE for octahedral complex}=[-0.4(n)t_{2g}+0.6(n^{\prime }\left)e_g\right]{\Delta }_o+n\ast P$ ​
Where, ​
n: Number of $e^{-}$ occupying $t_{2g}$ orbital ​
n': Number of $e^{-}$ occupying $e_g$ orbital​
${\Delta }_o$: Ligand field splitting energy​
$n^{\ast }$: Number of extra electron pairs ​
P: Spin-pairing energy​

The CFSE of a $d^7$ octahedral complex is
$=-0.4{\Delta }_o\times 6+0.6{\Delta }_o\times 1=-2.4{\Delta }_o+0.6{\Delta }_o=-1.8{\Delta }_o$
Hence, the correct option is (c).