Question

Sort the following complexes according to their crystal field stabilization energy (CFSE)

• A. $\left[Fe\right(CN{)}_6{]}^{3-}$
• B. $[{\mathrm{CoCl}}_6{]}^{4-}$
• C. $\left[\mathrm{Co}\right(\mathrm{CN}{)}_6{]}^{3-}$
• D. ${\left[Fe\right(H_{2}O{)}_6]}^{3+}$

Answer 1

$\left[Co\right(CN{)}_6{]}^{3-}$ : $C{o}^{3+}->$ $d^6$,
$C{N}^{-}$ is a strong ligand; low spin
CFSE = -2.4 ${\Delta }_o$

$\left[Fe\right(CN{)}_6{]}^{3-}$ : $F{e}^{3+}->$ $d^5$,
$C{N}^{-}$ is a strong ligand; low spin
CFSE = -2.0 ${\Delta }_o$

$\left[Fe\right(H_{2}O{)}_6{]}^{3+}$ : $F{e}^{3+}->$ $d^5$,
$H_{2}O$ is a weak ligand; high spin
CFSE = 0 ${\Delta }_o$

$[CoC{l}_6{]}^{4-}$ : $C{o}^{2+}->$ $d^7$,
$C{l}^{-}$ is a weak ligand; high spin
CFSE = -0.8 Δo