Question

Which of the following statement(s) is are true regarding $d^7$ configuration of octahedral complex in presence of strong field igand?

• A. The CFSE of a $d^7$ octahedral complex is $-1.8{\Delta }_o$.
• B. The CFSE of a $d^7$ octahedral complex is $-2.4{\Delta }_o$.
• C. The complex is low spin complex
• D. The configuration in splitted state will be $t_{2g}^6{e}_g^1$

Answer 1

Answer: (A), (C), (D)

The configuration in splitted state will be $t_{2g}^6{e}_g^1$

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 (a), (c) and (d) are correct.