Question

Consider the following metal complexes:
[Co(NH3)6]3+
[CoCl(NH3)5]2+
[Co(CN)6]3-
[Co(NH3)5(H2O)]3+
The spin-only magnetic moment value of the complex that absorbs light with shortest wavelength is _______ B.M. (Nearest integer)

Answer 1

In all complexes, Co is present in the +3 oxidation state and all complexes are low spin or inner orbital complex.
The stronger the ligand, the higher the crystal field splitting.
So, the order of crystal field splitting is
[Co(CN)6]3– > [Co(NH3)6]3+> [Co(NH3)5(H2O)]3+ > [CoCl(NH3)5]2+.
The shortest wavelength is shown by the complex having maximum crystal field splitting.
spin magnetic moment=$\sqrt{0(0+2)}$=0 BM