[Fe(H2O)6]3+ is strongly paramagnetic whereas [Fe(CN)6]3-is weakly paramagnetic. Explain.


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


Overall charge balance:


X + 6(0) = 3


X = + 3


In [Fe(CN)6]3-


Overall charge balance:


X + 6(-1) = -3


X = + 3


In both the compounds Fe is in + 3 oxidation state.



In case of [Fe(H2O)6]3+


H2O is weak field ligand so it does not pair the unpaired electron. Total no. of the unpaired electron, n = 5.


Spin only magnetic moment is given by:


μ = [n(n + 2)]1/2


μ = [5×7]1/2


μ = 5.916BM


In case of [Fe(CN)6]3-


CN- is a strong field ligand so it pairs up the electron.


Total no. of unpaired electrons = 1


Spin only magnetic moment is given by:


μ = [n(n + 2)]1/2


μ = [1×3]1/2


μ = 1.732BM


as we can see 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.



Fe in ground state


Fe in + 3 oxidation state


Electrons from 5 CN- ligands


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