Question

In the complex $Fe(CO{)}_x$, the value of x is:

• A. 3
• B. 4
• C. 5
• D. 6

Answer 1

Answer: (C)

5

Complex carbonyls follow Sidwick's EAN rule i.e compound with EAN 36 will be relatively more stable than other metal carbonyls.

Iron pentacarbonyl has EAN number of $36=Z-X+Y=(26-0+2x)$

[$Z=$ atomic number, $X=$ oxidation state of metal, $Y=$ total electrons donated by ligand]

$\therefore x=5$

So, the formula will be $Fe(CO{)}_5$.

Hence it exists in $Fe(CO{)}_5$ form.