Question

If the bond length of the C−O bond in CO is $1.128\stackrel{o}{A}$, what will be the value of the bond length in $\left[Fe\right(CO{)}_5]$?

• A. $1.158\stackrel{o}{A}$
• B. $1.128\stackrel{o}{A}$
• C. $1.101\stackrel{o}{A}$
• D. $1.118\stackrel{o}{A}$

Answer 1

The correct option is A $1.158\stackrel{o}{A}$

In free carbonyl, there will be no back bonding and the bond order of 'C-O' is 3.

In $Fe(CO{)}_5$, there will be back boding due to donation of electron from metal orbital to the carbonyls. Due to back bonding the bond order of 'M-C' increases and bond order of 'C-O' decreases. This result in increase in bond length of the 'C-O' than the free carbonyl.

Hence, only option (a) value is higher than $1.128\stackrel{o}{A}$.
Therefore, option (a) is correct.