Question

Which of the following complexes does not follow $EAN$ rule?

• A. $\left[Fe\right(CN{)}_6{]}^{4-}$
• B. $\left[Fe\right(CN{)}_6{]}^{3-}$
• C. $Ni(CO{)}_4$
• D. $\left[V\right(CO{)}_6{]}^{─}$

Answer 1

The correct option is B $\left[Fe\right(CN{)}_6{]}^{3-}$

According to sidgwick, ​
EAN=Number of electrons in central metal atom or ion​+Number of electrons donated by ligands​
The sum of electron on the central metal atomor ion and electrons donated from the ligands is called effective atomic number(EAN).
$EAN$ = atomic number of nearest noble gas.
$EAN=Z-O.S+2\times C.N$
Z=atomic number of central metal atom
O.S=Oxidation state of central metal atom
C.N=coordination number of ligands.

$\left[Fe\right(CN{)}_6{]}^{4-}$
$Z=26$
$O.S=+2$
$C.N=6$
$EAN=26-2+2\times 6=36$
While, the atomic number of nearest noble gas is 36. Thus, it follow $EAN$ rule.

$\left[Fe\right(CN{)}_6{]}^{3-}$
$Z=26$
$O.S=+3$
$C.N=6$
$EAN=26-3+2\times 6=35$
While, the atomic number of nearest noble gas is 36. Thus, it does not follow $EAN$ rule.

$\left[Ni\right(CO{)}_4]$
$Z=28$
$O.S=0$
$C.N=4$
$EAN=28-0+2\times 4=36$
While, the atomic number of nearest noble gas is 36. Thus, it follow $EAN$ rule.

$\left[V\right(CO{)}_6{]}^{─}$
$Z=23$
$O.S=-1$
$C.N=6$
$EAN=23+1+2\times 6=36$
While, the atomic number of nearest noble gas is 36. Thus, it follow $EAN$ rule.