Ex : Apply the concept of EAN rule on the complexes [Fe(CN)6]4− and [Fe(CN)6] 3−. What conclusion you draw about the validity of the EAN rule from these two well‐known complexes? [Atomic number of Fe = 26].
Solution : (a) Let us take the case [Fe(CN)6]4−
Oxidation state of Fe in [Fe(CN)6]4− = +2
No. of electrons in iron = 26
∴ No. of electrons in Fe(II) of the complex = 26−2 = 24
Number of electrons donated by six CN− ligands = 6×2 = 12
∴ EAN of Fe(II) in [Fe(CN)6]4− = 24+12 = 36
Since, this number (36) = number of electrons in the atom of the nearest noble gas (Kr),
the complex [Fe(CN)6]4− follows the EAN rule or the EAN rule is valid on this complex.
(b) Now let us take the case of [Fe(CN)6]3−
Oxidation state of iron = +3
∴ Number of electrons in Fe(III) of the complex = 26−3 = 23
Number of electrons donated by six CN− ligands = 12
∴ EAN of Fe (III) in [Fe(CN)6]3− = 23+12 = 35
Since, this number (35) is different from the electrons present in the next noble gas (Kr = 36), we can say that the EAN rule is not valid on this complex.