Question

Which of the following metal carbonyl does not exist as monomer?

• A. $Cr(CO{)}_6$
• B. $Mn(CO{)}_5$
• C. $Ni(CO{)}_4$
• D. $Fe(CO{)}_5$

Answer 1

The correct option is B $Mn(CO{)}_5$

EAN of compound (a), (c) and (d) are 36. Hence, it obeys EAN rule.
EAN of $Mn(CO{)}_5$ is
$=25-0+2\times 5$
$=35$
It does not obey EAN rule, thus, it is less stable. Hence, it is undergo dimerisation to form $M{n}_2(CO{)}_{10}$