Question

Find the number of complexes in which has stability greater than the stability of $[Fe{F}_6{]}^{3-}$
$\left[Fe\right(CN{)}_6{]}^{3-},\left[Fe\right(ox{)}_3{]}^{3-},\left[Fe\right(N{H}_3{)}_6{]}^{3+},\left[Fe\right(H_{2}O{)}_6{]}^{3+},\left[Fe\right(en{)}_3{]}^{3+}$

Answer 1

All the complexes given are octahedral.

$[Fe{F}_6{]}^{3-},[Fe(ox{)}_3{]}^{3-},[Fe(H_{2}O{)}_6{]}^{3+}$ are high spin complexes with electronic configuration

$t_{2g}^3{e}_g^2$
Hence crystal field stabilization energy = ${\Delta }_0=(-0.4\times 3+0.6\times 2+0\times (pairingenergy)=0$


$\left[Fe\right(CN{)}_6{]}^{3-},\left[Fe\right(N{H}_3{)}_6{]}^{3+},\left[Fe\right(en{)}_3{]}^{3+}$ are low spin complexes with electronic configuration
$t_{2g}^5{e}_g^0$

Hence crystal field stabilization energy = ${\Delta }_0=(-0.4\times 5+0.6\times 0+2\times (pairingenergy)$
which is not equal to zero.