[FeF6]3– ion paramagnetic while [Fe(CN)6]4–ion diamagnetic

Why is [FeF₆]^3– ion paramagnetic while [Fe(CN)₆]^4–ion diamagnetic ?

In case of [FeF₆]^3–complex ion, the oxidation state of central iron metal is +3. 

The atomic number of iron metal : 26 and that of ion(III)ion : 23. Valence shell electronic configuration of Fe(III) ion : [ Ar ] d⁵ .

Co-ordination number of central metal Fe(III)ion : 6. Arrangement of [FeF₆]^3– complex ion : Octahedral.

Now ligand F^–, which is a weak field ligand. Under the influence of the octahedral 

crystal field, the five degenerate d-orbitals of Fe(III) ion are splitted into two sets of  energetically different orbitals.

These two sets of orbitals are energetically lower t_2g orbital and energetically higher e_g orbital.

Since ligand F^–, is a weak field ligand, hence the complex is high spin one.

So, under the influence of the octahedral crystal field, the possible electronic arrangement of Fe(III) ion is t2g³, eg².

The octahedral crystal field splitting of [FeF₆]^3– complex ion is as follows,

From the above crystal field splitting diagram of Fe(III) ion, it is evidently, shown that, the Fe(III)ion have five unpaired electrons in its outer 3d-orbital. 

Hence, hexafluoridoferrate(III) ion,  [FeF₆]^3– is paramagnetic in nature.

On the other hand, in case of [Fe(CN)₆]^4–ion, the oxidation state of iron is +2 .

The ligand CN^– which is a strong  field ligand. Now, the valence shell electronic configuration of Fe(II) ion is [ Ar ] d⁶ .

Again, since the ligand CN^– is a strong field ligand, hence the complex is low spin one.

Therefore, under the influence of the octahedral crystal field, the possible electronic arrangement of Fe(II) ion is t2g⁶, eg⁰.

The octahedral crystal field splitting of [Fe(CN)₆]^4–complex ion is as follows,

From the above crystal field splitting diagram of Fe(II) ion, it is evidently  shown that, the Fe(II)ion have no unpaired electrons in its outer 3d-orbital.

That is, all electrons are paired, hence [Fe(CN)₆]^4–complex ion is diamagnetic in nature.

Why is [FeF₆]^3– ion paramagnetic while [Fe(CN)₆]^4–ion diamagnetic ?

Why is [FeF₆]^3– complex ion paramagnetic ?

Why is [Fe(CN)₆]^4– complex ion diamagnetic ?

What is octet rules? explain with examples