Question

Which complex compound obeys 18-electron rule?

• A. $\left[V\right(CO{)}_5]$
• B. $\left[Fe\right(N{H}_3{)}_6{]}^{2+}$
• C. $\left[Ni\right(CO{)}_6]$
• D. $\left[Mn\right(H_{2}O{)}_6{]}^{2+}$

Answer 1

The correct option is B $\left[Fe\right(N{H}_3{)}_6{]}^{2+}$

The rule states that thermodynamically stable transition metal organometallic compounds are formed when the sum of the metal d electrons and the electrons conventionally considered as being supplied by the surrounding ligands equals 18.
$\left[V\right(CO{)}_5]=5+5\times 2=15e^{-}$
$\left[Fe\right(N{H}_3{)}_6{]}^{2+}=8+6\times 2-2=18e^{-}$
$\left[Ni\right(CO{)}_6]=10+6\times 2=22e^{-}$
$\left[Mn\right(H_{2}O{)}_6{]}^{2+}=7+6\times 2-2=17e^{-}$