Explain why [Fe(H2O)6]3+ has high magnetic moment value of 5.92 BM whereas magnetic moment of [Fe(CN)6]3– has value of only 1.74 BM.
In [Fe(H2O)6]3+
Electronic configuration of Fe is: [Ar]3d64s2
[Ar] = 1s22s22p63s23p6
Electronic configuration of Fe+3 = [Ar]3d5
Outer electronic configuration of Fe+3 = 3d5
Oxidation number of Fe is +3
The electrons remain unpaired because H2O is weak field ligand. Total no. of the unpaired electron, n = 5.
We know,
Spin only magnetic moment is given by:
μ = [n(n + 2)]1/2
μ = [5×7]1/2 [As, unpaired electrons are 5]
μ = 5.916BM
Hybridization is sp3d2.
In case of [Fe(CN)6]3-
Electronic configuration of Fe is: [Ar]3d64s2
[Ar] = 1s22s22p63s23p6
Electronic configuration of Fe+3 = [Ar]3d5
Outer electronic configuration of Fe+3 = 3d5
Oxidation number of Fe is +3
Hybridization is d2sp3
Since, CN- is a strong field ligand so it pairs up the electron.
Thus, total no. of unpaired electrons = 1
We know,
Spin only magnetic moment is given by:
μ = [n(n + 2)]1/2
μ = [1×3]1/2 [As, unpaired electrons are 1]
μ = 1.732BM
Therefore, we can see that spin only magnetic moment of [Fe(H2O)6]3+ is more than [Fe(CN)6]3- .
so, [Fe(H2O)6]3+ is strongly paramagnetic whereas [Fe(CN)6]3 weakly paramagnetic.
