Question

If ${\Delta }_0$ is the octahedral crystal field splitting energy.
Then the CFSE for $Fe(CN{)}_6{]}^4-$ is: (ignore pairing energy)

• A. $-2.4{\Delta }_0$
• B. $-0.4{\Delta }_0$
• C. $-2.0{\Delta }_0$
• D. $-0.6{\Delta }_0$

Answer 1

Answer: (A)

$-2.4{\Delta }_0$

In the given complex the Fe is in +2 oxidation state and hence the configuration is $3d^6$ and since the ligand is a strong field ligand therefore the the excitation energy is greater than pairing energy therefore the configuration is $t_2{g}^{6}e{g}^0$ and hence the CFSE= -0.4${\Delta }_o$ x 6 = -2.4${\Delta }_o$ . Therefore the correct option is A.