Question

Which of the following complexes does not obey the EAN rule?

• A. $[PtCl_6]^{2-}$
• B. $[Co(NH_3)_6]^{3+}$
• C. $[Fe(CN)_6]^{3-}$
• D. $[Cu(CN)_4]^{3-}$

Answer 1

Answer: (C)

EAN rule means that the effective atomic number of the central metal must be equal to the atomic number of next noble gas.
For $[Fe(CN)_6]^{3-}$, Fe is in +3 oxidation state.
EAN $= 26 - 3 + (6 \times 2) = 35$
35 is not equal to the atomic number of the next noble gas Kr (36).