Question

In the isoelectronic series of metal carbonyls, the 'M-C' bond strength is expected to increase in the order:

• A. $\left[Cr\right(CO{)}_6]<[Mn(CO{)}_6{]}^{+}<[V(CO{)}_6{]}^{-}$
• B. $\left[V\right(CO{)}_6{]}^{-}<\left[Cr\right(CO{)}_6]<[Mn(CO{)}_6{]}^{+}$
• C. $\left[V\right(CO{)}_6{]}^{-}<\left[Mn\right(CO{)}_6{]}^{+}<\left[Cr\right(CO{)}_6]$
• D. $\left[Mn\right(CO{)}_6{]}^{+}<\left[Cr\right(CO{)}_6]<[V(CO{)}_6{]}^{-}$

Answer 1

The correct option is D $\left[Mn\right(CO{)}_6{]}^{+}<\left[Cr\right(CO{)}_6]<[V(CO{)}_6{]}^{-}$

We know,
More the extent of back bonding, higher will be the bond order of $M-C$. Thus, higher will be its bond strength.

Comparing the oxidation state of Mn, Cr and V, $Mn$ has highest oxidation so it has least ability to donate electrons to the carbonyl compare to others so it has the weakest 'M-C' bond strength and $V$ has the lowest oxidation state so it has the highest ability to donate electrons to the carbonyl and it has the strongest 'M-C' bond strength.

Hence, option (a) is correct.