Question

$\left[Fe\right(CN{)}_6{]}^{-3}$ is low spin complex but $\left[Fe\right(H_{2}O{)}_6{]}^{+3}$ is high spin complex. Explain.

Answer 1

According to spectrochemical series, ${CN}^{-}$ is a strong field ligand and can pair electrons while $H_{2}O$ is a weak field ligand and thus cannot pair electron.

Hence due to presence of unpaired electrons, ${\left[Fe{\left(H_{2}O\right)}_6\right]}^{+3}$ is a high spin complex while ${\left[Fe{\left(CN\right)}_6\right]}^{-3}$ is a low spin complex.