Question

Which of the following does not follow EAN rule?

• A. $ V(CO)_{6} $
• B. $ Cr(CO)_{6} $
• C. $ Mn(CO)_{6} $
• D. $ W(CO)_{6} $

Answer 1

Answer: (A)

EAN Rule: The metal ion will continue accepting electron pairs till the total number of electrons in the metal ion and those donated by ligands is equal to that of the next higher noble gas.
This total number of electrons is called effective atomic number (EAN) of the metal $ V(CO)_{6} \to $ Number of electrons $= 23$
Number of electrons donated by $6 \,CO =6\times 2=12 $
Total number of electrons $= 23 + 12 = 35 $ does not follow EAN rule
$ Cr(CO)_{6} \to $ Number of electrons $= 24$
Number of electrons donated by $6\,CO =6\times 2=12 $
Total number of electrons $= 24 + 12 = 36$ follow EAN rule
$Kr = 36$ (next noble gas) $ Mn(CO)_{6} \to $
Number of electrons $= 25$
Number of electrons donated by $6CO =2\times 6=12 $
Total number of electrons $= 25 + 12 = 37$ does not follow EAN rule
$ W(CO)_{6} \to $ Number of electrons $= 74$
Electrons donated by $ 6CO=2\times 6=12 $
Total number of electrons $= 74 + 12 = 86$ follow EAN rule
$ Rn=86 $ (next noble gas)