Tag: metal carbonyls

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Multiple choice chemistry coordination chemistry bonding in metal carbonyls metal carbonyls coordination compounds
The π acid ligands donate their lone pairs to the metal to form a normal σ bond with the latter in addition to it, the vacant orbitals accept e− from the filled metal orbitals to form a type of π−bond which supplements the σ bond.

Which of the following has lowest C-O bond length ?
  1. $[Ni(CO) _4]$
  2. $[Co(CO) _4]^{-}$
  3. $[Fe(CO) _4]^{2-}$
  4. $[Mn(CO) _6]^+$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

This type of bonding where a metal is bonded with the carbon of a carbonyl compound is known as synergic bonding. In a metal carbonyl, the M-C bond has both σ and π character. The ligand donates eΘ pair to the central metal atom, and simultaneously accepts eΘ pair from central metal atom through synergic bonding. Here, all the options are examples of organometallic compounds. Due to synergic bonding, the metal carbon bond strength increases and bond length decreases due to the partial double bond character. Thus, the C-O bond strength decreases and bond length increases and bond order of CO decreases as the number of antibonding electrons increase. Out of the four options, the option D has Mn+, implying that the electron donating nature among the options is minimum. Therefore, tendency of synergic bonding is minimum, and thus M-C bond length is maximum implying that C-O bond strength is maximum and C-O bond length is minimum.

Multiple choice chemistry coordination chemistry bonding in metal carbonyls metal carbonyls coordination compounds

The pi acceptor ligand are those which possess vacant $\pi$-orbitals in addition to the lone pairs of $e^-$,which of the following complex/ion has highest M-C bond order?

  1. $[V(CO) _6]^{-}$
  2. $Fe(CO) _5$
  3. $Ni(CO) _4$
  4. $[Mn(CO) _6]^+$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The M-C bond order is highest when there is the most back-bonding. This occurs in the anionic complex [V(CO)6]-, which has the highest electron density on the metal to donate into the CO pi-star orbitals.

Multiple choice chemistry coordination chemistry bonding in metal carbonyls metal carbonyls coordination compounds

Which of the following complex/ion has lowest C-O bond order ?

  1. $[V(CO) _6]^-$
  2. $Fe(CO) _5$
  3. $Ni(CO) _4$
  4. $[Mn(CO) _6]^+$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

There are vacant orbitals in central atom in $[V(CO) _6]-$ which results in synergic bonding. Due to synergic bonding between V and CO the bond length between C and O increases and Bond order is inversely proportional to bond length.

Multiple choice chemistry coordination chemistry bonding in metal carbonyls metal carbonyls coordination compounds

The pi acceptor ligand are those which possess vacant $\pi$-orbitals in addition to the lone pairs of $e^-$which of the following complex/ion has lowest M-C bond length ?

  1. $[V(CO) _6]^-$
  2. $Fe(CO) _5$
  3. $Ni(CO) _4$
  4. $[Mn(CO) _6]^+$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Stronger M-C bonds (higher bond order from more back-bonding) result in shorter bond lengths. [V(CO)6]- has the strongest back-bonding (most electron-rich metal), so it has the shortest M-C bond length. Option D is an error.

Multiple choice chemistry coordination chemistry bonding in metal carbonyls metal carbonyls coordination compounds

Which of the following is/are example( s) of $\sigma$-bonded organometallic compound ? 

  1. Al$ _2$(CH$ _3$)$ _6$
  2. Pb(CH$ _3$)$ _4$
  3. Zn(C$ _2$H$ _5$)$ _2$

  4. Ferrocene
Reveal answer Fill a bubble to check yourself
A,B,C Correct answer
Explanation

Option (A),(B),(C) are correct.Ferrocene is example of organometallic compound but is not $\sigma$-bonded. Its formula is $Fe(C _5H _5) _2$. It is the prototypical metallocene, a type of organometallic chemical compound consisting of two cyclopentadienyl rings bound on opposite sides of a central metal atom. Such organometallic compounds are also known as sandwich compounds. Each cyclopentadienyl (Cp) ring is then allocated a single negative charge, bringing the number of -electrons on each ring to six, and thus making them aromatic. These twelve electrons (six from each ring) are then shared with the metal via covalent bonding. 

Multiple choice chemistry coordination chemistry bonding in metal carbonyls metal carbonyls coordination compounds

Which of the following statement(s) is/are incorrect ? 

  1. Metal carbonyls are the examples of only $\sigma$-bonded organometallic complexes.
  2. Metal carbonyls are the examples of only $\pi$-bonded organometallic complexes.
  3. Metal carbonyls are the examples of organometallic complexes which involve both $\sigma$- and $\pi$-bonds between metal and carbon of the carbonyl group.
  4. Metal carbonyls involve both $\sigma$- and $\pi$-bonds between metal and oxygen of the carbonyl group.
Reveal answer Fill a bubble to check yourself
A,B,D Correct answer
Explanation

Metal carbonyls involve synergistic bonding where the metal donates electrons into the CO pi-antibonding orbital (pi-backbonding) and CO donates electrons into the metal d-orbitals (sigma-bonding). Therefore, they are not examples of only sigma or only pi bonded complexes, making statements A, B, and D incorrect.

Multiple choice chemistry coordination chemistry bonding in metal carbonyls metal carbonyls coordination compounds

Among the following complexes, the C-O bond order is lowest in :

  1. [Mn(CO)$ _6$]$^+$
  2. [Fe(CO)$ _5$]
  3. [Cr(CO)$ _6$]
  4. [V(CO)$ _6$]$^-$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The C-O bond order decreases as the extent of metal-to-ligand pi-backbonding increases. This backbonding is enhanced by a higher negative charge on the metal complex, which increases electron density on the metal center.

Multiple choice chemistry coordination chemistry bonding in metal carbonyls metal carbonyls coordination compounds

If the bond length of the C - O bond in CO is 1.128$\overset{o}{A}$ what is the value of the bond length in [Fe(CO)$ _5$] ?

  1. $1.15$ $\overset{o}{A}$
  2. $1.128$ $\overset{o}{A}$
  3. $1.72$ $\overset{o}{A}$
  4. $1.118$ $\overset{o}{A}$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

In metal carbonyl complexes like Fe(CO)5, back-bonding from the metal d-orbitals to the pi* antibonding orbitals of CO weakens the C-O bond and increases its bond length compared to free carbon monoxide.