When the ligands are arranged in order of the magnitude of crystal field splitting, the arrangement, thus, obtained is called spectrochemical series.
Arranged in increasing field strength as
I−<Br−<Cl−<NO3−<F−<OH−<C2O42−<H2O<NH3<en<NO2<CN−<CO
It has been observed that ligands before
H2O are weak fields ligands while ligands after
H2O are strong field ligands.
CFSE in octahedral field depends upon the nature of ligands. Stronger the ligands larger will be the value of
Δoct