Chemistry

Coordination Chemistry

319 Questions

Coordination chemistry focuses on coordination compounds, their structures, and their magnetic properties. The questions cover primary and secondary valencies, ligand types, and geometries of complexes. This topic is heavily tested in chemistry competitive exams and requires a good grasp of molecular structures.

primary and secondary valencycomplex geometriesligand field theorymagnetic properties of complexesisomerism in complexes

Coordination Chemistry Questions

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

Which of the following statement is correct regarding metal carbonyl?

  1. In ${Mn} _{2}{(CO)} _{10}$ bond order of $Mn-Mn$ is $0$
  2. In ${Fe} _{2}{(CO)} _{9}$ bond order of $Fe-Fe$ is $1$
  3. In $Ni{(CO)} _{4}$, all bond length are same
  4. $Fe{(CO)} _{5}$ is diamagnetic
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Fe(CO)5 is a 18-electron complex with a trigonal bipyramidal structure. All electrons are paired in the d-orbitals, making it diamagnetic.

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

Which of the following organometallic compound

is $\sigma $ and $\pi $ bonded?

  1. $[Fe(\eta ^{5}-C _{5}H _{5}) _{2}]$
  2. $[PtCl _{3}(\eta ^{2}-C _{2}H _{4})]$
  3. $[Co(CO) _{5}NH _{3}]^{2+}$
  4. $Al(CH _{3}) _{3}$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

$[PtCl _{3}(\eta ^{2}-C _{2}H _{4})]$ and $[Fe(\eta ^{5}-C _{5}H _{5}) _{2}]$ are pi bonded organometallic compound.

$Al(CH _3) _3$ 
is sigma bonded organometallic compound.
$[Co(CO) _{5}NH _{3}]^{2+}$ is sigma and pi bonded organometallic compound.

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

Which of the following organometallic compound is $\sigma$ and $\pi$ bonded -

  1. $[Fe(\eta^{5} - C _5H _5) _2]$
  2. $K[PtCl _3(\eta^{2} - C _2H _40]$
  3. $[Co(CO) _5NH _3]^{+2}$
  4. $Fe(CH _3) _3$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation
Option (C) is correct.
$[Co(CO) _5NH _3]^{+2}$ is $\sigma$ and $\pi$ bonded.
In this organometallic compound,bond between cobalt and $CO$ ligands have both $\sigma$ and $\pi$ character.$\sigma$- bond formation between metal and carbon of $CO$ takes place by overlap of filled bonding $\pi _{2p}$ of $CO$ with an empty metal $d$- orbital.
The 2nd overlap takes place between metal $d$- orbital with an empty antibonding pi orbital of the $CO$ resulting in additional $\pi$- bond between the metal and same $CO$ molecule. 
Multiple choice chemistry coordination chemistry bonding in metal carbonyls metal carbonyls coordination compounds

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

  1. In metal carbonyl complexes $d _{C-O}$ increases compared to that in CO molecule
  2. The pair of compounds $[Cr(H _2O) _6]Cl _3$ and $[CrCl _3(H _2O) _3]\cdot 3H _2O$ show hydrate isomerism.
  3. $d _{z^2}$ orbital of central metal atom/ion is used in $dsp^2$ hybridisation.
  4. Facid and Meridional isomers associated with $[Ma _3b _3]^{n\pm}$ type complex compound, both are optically inactive.
Reveal answer Fill a bubble to check yourself
A,D Correct answer
Explanation

(A) Metal carbonyls involve synergic bonding $(M\underset {\sigma}{\overset {\pi}\rightleftharpoons } L)$. Filled metal d orbital overlaps with antibonding pi orbital of CO. Thus the bond order and bond length in CO decreases.
Thus option A is correct.
(B) $[CrCl _3(H _2O) _3]\cdot 3H _2O$ is not a hydrate isomer of $[Cr(H _2O) _6]Cl _3$.
Thus option B is incorrect.
(C) The d-orbitals involved in s$sp^3d^2  and\  d^2sp^3$  hybridisation of the central metal ion are $d _{x^2-y^2}$  and  $d _{z^2}$ respectively.
Thus option C is incorrect.
(D) Both fac and mer isomers of $[Ma _3b _3]^{n\pm}$ are optically inactive as they contain plane of symmetry.
Thus option D is correct.

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

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

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

  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;
Reveal answer Fill a bubble to check yourself
A Correct answer
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.
Multiple choice chemistry coordination chemistry bonding in metal carbonyls metal carbonyls coordination compounds

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

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
B Correct answer
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.
Multiple choice chemistry coordination chemistry bonding in metal carbonyls metal carbonyls coordination compounds

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 :

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