Question

Which of the following does not obey 18-electron rule?

• A. $Cr(CO{)}_6$
• B. $Fe(CO{)}_5$
• C. $V(CO{)}_6$
• D. $M{n}_2(CO{)}_{10}$

Answer 1

Answer: (C)

$V(CO{)}_6$

V atom in $V(CO{)}_6$ contains $17$ valence electrons. $12$ electrons are from $6$ $CO$ ligands and $7$ electrons are from $V$. Hence, the complex does not obey $18$ - electron rule.

$Cr(CO{)}_6,Fe(CO{)}_5$ and $M{n}_2(CO{)}_{10}$ all contains $18$ valence electrons on the central metal atom. Hence, they follow $18$ electron rule.