Question

Pick out the complex compound in which the central metal atom obeys EAN rule strictly :

• A. $K_4\left[Fe\right(CN{)}_6]$
• B. $K_3\left[Fe\right(CN{)}_6]$
• C. $\left[Cr\right(H_{2}O{)}_6]C{l}_3$
• D. $\left[Cu\right(N{H}_3{)}_4]S{O}_4$

Answer 1

Answer: (A)

$K_4\left[Fe\right(CN{)}_6]$

In a metal complex, the metal atom tends to surround itself with sufficient ligands that the resulting effective atomic number is numerically equal to the atomic number of the noble gas element found in the same period in which the metal is present.

In $K_4\left[Fe\right(CN{)}_6]$, he central metal atom obeys EAN rule strictly.

$EAN=Z-X+2Y=26-2+12=36$

$Z=$ atomic number of metal
$X=$ number of electrons lost while forming metal ion
$Y=$ number of electrons donated by ligands

The $EAN$ is equal to the atomic number of the nearest noble gas $Kr$.