Tag: metal carbonyls

Questions Related to metal carbonyls

Match the column :

Column-I Column-II
(a) $[Fe(CO) _4]^{2-}$ (p) Complex having lowest bond length of CO ligand
(b) $[V(CO) _6]^{-}$ (q) Follow Sidgwick's rule of E.A.N.
(c) $K[PtCl _3(C _2H _4)]$ (r) Synergic bonding is involved in complex/ion
(d) $[Fe(H _2O) _5NO]SO _4$ (s) Complex having highest bond length of CO ligand
(t) Oragnometallic compound
chemistry coordination chemistry bonding in metal carbonyls metal carbonyls coordination compounds

  1. (a) q,r,s,t; (b) p,q,r,t; (c) r,t; (d) r

  2. (a)s,t; (b) p,q,r,t; (c) r; (d) r

  3. (a) q,s,t; (b) q,r,t; (c) r,t; (d) r

  4. (a) q,r,t; (b) q,r,t; (c) r;

Show answer
Correct Option: A
Explanation:
(a) The complex $[Fe(CO) _4]^{2-}$
(q) Follow Sidgwick's rule of E.A.N.
(r) Synergic bonding is involved in complex/ion
(s) Complex having highest bond length of CO ligand
(t) Oragnometalic compound
(b) The complex  $[V(CO) _6]^{\Theta}$
(p) Complex having lowest bond length of CO ligand
(q) Follow Sidgwick's rule of E.A.N.
(r) Synergic bonding is involved in complex/ion
(t) Oragnometalic compound
(c) The complex  $K[PtCl _3(C _2H _4)]$
(r) Synergic bonding is involved in complex/ion
(t) Oragnometalic compound

(d) The complex  $[Fe(H _2O) _5NO]SO _4$
(r) Synergic bonding is involved in complex/ion


Effective atomic number (EAN) is number that represents the total number of electrons surrounding the nucleus of a metal atom in a metal complex. 
It is composed of the metal atom’s electrons and the bonding electrons from the surrounding electron-donating atoms and molecules.
In Synergic bonding, the ligand donates its electron density to metal and the metal in turn backdonates its electron density to ligand.
The back donation reinforce the sigma bond, and vice versa. This type of bonding has been called the synergic bonding 
Organometallic compounds have bonds between metal atom and C atom.

If the bond length of $CO$ bond in carbon monoxide is 1.128 $\overset{o}A$, then what is the value of $CO$ bond length in $Fe$$(\mathrm{C}\mathrm{O}) _{5}$? 

chemistry coordination chemistry bonding in metal carbonyls metal carbonyls coordination compounds

  1. 1.15 $\overset{o}A$

  2. 1.128 $\overset{o}A$

  3. 1.72 $\overset{o}A$

  4. 1.178 $\overset{o}A$

Show answer
Correct Option: A
Explanation:

The metal (Fe) makes the back bonding to CO. The metal to ligand bonding creates a synergic effect which strengthens the bond between CO and the metal (Fe).Which results in the contraction of CO bond length.

$[Ni(CO) _{4}]>[Co(CO) _{4}]^{-}>[Fe(CO) _{4}]^{2-}$ is the correct order with respect to M-C $\pi$ bond. Where M=Ni, Fe, and Co

chemistry coordination chemistry bonding in metal carbonyls metal carbonyls coordination compounds

  1. True

  2. False

Show answer
Correct Option: B
Explanation:
In carbonylate anion, the metal has a greater electron density to
be dispersed, with the result that M-C, $\pi $ bonding is enhanced in
strength. Hence the correct order is$[Ni(CO) _{4}]<[Co(CO) _{4}]^{-}<[Fe(CO) _{4}]^{2-}$. for strength of M - C$\pi $ bond.

Among the metal carbonyls $[Mn(CO) _6]^+, [Ti(CO) _6], [Cr(CO) _6]$ and $[V(CO) _6]^-$ the $C-O$ bond order would be lowest in :

chemistry coordination chemistry bonding in metal carbonyls metal carbonyls coordination compounds

  1. $[Mn(CO) _6]^+$

  2. $[Ti(CO) _6]^{2-}$

  3. $[Cr(CO) _6]$

  4. $[V(CO) _6]^-$

Show answer
Correct Option: A
Explanation:

The $C-O$ bond order would be lowest at $[Mn(CO) _6]^+$. 


The metal bears a positive charge which makes the back donation process favourable. 

The electrons from the metal fill the $\pi -$ antibonding orbital of CO, they weaken the carbon-oxygen bond.

Hence, the correct option is A.

If in the mixed carbonyl, the other ligand is also pi acceptor, it would compete with the ligand CO for gaining the metal $d _\pi$ electron charge. The higher is the extent of back donation in CO, the lesser will be the stretching vibration frequency for C-O bond. If $PF _3$ is better $\pi$-acceptor than CO, then answer the following.


Select the correct order of stretching vibration frequency C-O bond in the following molecules :

chemistry coordination chemistry bonding in metal carbonyls metal carbonyls coordination compounds

  1. $[Ni(CO) _4] > [Ni(PF _3)(CO) _3]$

  2. $[Ni(CO) _4] < [Ni(CO) _3 (PF _3)]$

  3. $[Ni(CO) _4] = [Ni(PF _3)(CO) _3]$

  4. Can not predicted

Show answer
Correct Option: B
Explanation:

If $PF _3$ is a better $\pi$-acceptor ligand than CO, then
extent of back donation from $M \overset{\pi}{\rightarrow} C \equiv O$ decreases, and hence bond order of CO will less decrease.
Stretching frequency of C - O bond $\propto$ bond order of C $\equiv$ O.
Therefore, stretching frequency of $[Ni(PF _3)(CO) _3] >  [Ni(CO) _4]$.