Chemistry

Coordination Chemistry

325 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

What is the donor atom in the coordination compound [Co(NH3)6]Cl3?

  1. Hydrogen

  2. Nitrogen

  3. Chlorine

  4. Cobalt
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

In coordination compounds, donor atoms are ligand atoms that directly coordinate to the central metal ion. In [Co(NH3)6]Cl3, ammonia (NH3) ligands coordinate through nitrogen atoms. Chlorine is outside the coordination sphere as a counterion.

Multiple choice

Which of the following coordination compounds does not show optical activity?

  1. [Co (NH3)3 Cl3]

  2. [Co (en)2 Cl2]+

  3. [Co (NH3)6] Cl3

  4. [Co (edta)]
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Optical activity requires non-superimposable mirror images (chirality). [Co(NH3)6]Cl3 has six identical ammonia ligands in octahedral geometry with perfect symmetry - it has multiple planes and axes of symmetry, making it achiral. The other compounds have asymmetric arrangements.

Multiple choice

What is the coordination number of [Cr(C2O4)3]3-?

  1. 1

  2. 2

  3. 4

  4. 6
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The oxalate ion (C2O4)2- is a bidentate ligand, coordinating through two oxygen atoms. In [Cr(C2O4)3]3-, three oxalate ligands each donate two electron pairs, giving 3×2=6 donor atoms bonded to chromium, so CN=6.

Multiple choice

Which of the following geometries is possessed by complex Fe(CO)5?

  1. Square planar

  2. Tetrahedral

  3. Trigonal planar

  4. Trigonal bipyramidal
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Fe(CO)5 is iron pentacarbonyl, a neutral coordination complex. With five CO ligands around a central metal ion, the only stable geometry that minimizes repulsion while satisfying the 18-electron rule is trigonal bipyramidal. Square planar would require only 4 ligands, tetrahedral geometry with 5 ligands is unstable, and trigonal planar only accommodates 3 ligands.

Multiple choice

Which of the following complexes are examples of linkage isomerism?

  1. [Co(NH3)5ONO]2+ and [Co(NH3)5NO2]2+

  2. [Co(NH3)4Cl2] NO2 and [Co(NH3)4 (Cl) NO2] Cl

  3. [Co(py)2 (H2O)2Cl2]Cl and [Co(py)2 (H2O)Cl3] H2O

  4. [Co(NH3)4 Cl2]NO2 and [Co(NH3)4(Cl)NO2]Cl
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Linkage isomerism occurs when ambidentate ligands can bind through different donor atoms. The nitrite ion (NO2-) is a classic ambidentate ligand that can bind through nitrogen (nitro: -NO2) or through oxygen (nitrito: -ONO). The two complexes [Co(NH3)5ONO]2+ and [Co(NH3)5NO2]2+ differ only in which atom binds to cobalt, making them linkage isomers.

Multiple choice

Assertion: In complex [Mn(H2O)6]+2, the d-d transitions are spin allowed. Reason: Each of the d-orbitals of Mn(II) is singly occupied.

There are two statements, Assertion (A) and Reason (R). Consider both the statements independently and mark your answer as under:

1. A and R are both correct and R is the correct explanation of A.
2. A and R are both correct and R is not the correct explanation of A.
3. A is correct and R is incorrect.
4. A is incorrect and R is correct.
5. A and R are both incorrect.

  1. A and R are both correct and R is the correct explanation of A.

  2. A and R are both correct and R is not the correct explanation of A.

  3. A is correct and R is incorrect.

  4. A is incorrect and R is correct.

  5. A and R are both incorrect.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

This option is correct because in case of [Mn(H2O)6]+2, the d-d transitions are spin forbidden because each of the d-orbitals is singly occupied (half filled) and the spin multiplicity changes when the electron goes to an excited state from ground state.

Multiple choice

The ground state term symbol for trivalent niobium ion is

  1. 3F2

  2. 5D0

  3. 2D5/2

  4. 1S0

  5. 4F3/2
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

S = ½ x number of unpaired electrons = ½ x 2 = 1 2S + 1 = 2 x 1 + 1 = 3 L = 3 for d2 ion configuration for which the ground term is F J = L - S = 3 - 1 = 2 The ground state term is (2S + 1)LJ = 3F2 Thus, this option is correct.

Multiple choice

Assertion: Complex [Co(NH3)3F]+2 gives absorption bands in the far ultra-violet region but in complex [Co(NH3)3Br]+2, absorption occurs at a longer wavelength. Reason: These peaks are of low intensity and their extinction coefficients are usually between 1 and 50.

There are two statements, Assertion (A) and Reason (R). Consider both the statements independently and mark your answer as under:

 1. A and R are both correct and R is the correct explanation of A.
2. A and R are both correct and R is not the correct explanation of A.
3. A is correct and R is incorrect.
4. A is incorrect and R is correct.
5. A and R are both incorrect.

  1. A and R are both correct and R is the correct explanation of A.

  2. A and R are both correct and R is not the correct explanation of A.

  3. A is correct and R is incorrect.

  4. A is incorrect and R is correct.

  5. A and R are both incorrect.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Complex [Co(NH3)3F]+2 absorbs in the far ultra-violet region but in complex [Co(NH3)3Br]+2, absorption occurs at a longer wavelength. It is so because the position of the charge transfer band depends on the nature of the metal and the ligand.

Multiple choice

Which of the following statements is/are correct?

  1. The intensity of a spin forbidden transition is about one-hundredth of that of a spin allowed transition.
  2. For d2 configuration, the ground state terms 3F and 3P are considered.
  3. The intense red color of [Fe(SCN)6]+3 ion is due to metal to ligand charge transfer spectra.

  1. Only 1

  2. Only 2

  3. Only 3

  4. 1 and 2

  5. 2 and 3
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

This option is correct because the intensity of spin forbidden transition is about one-hundredth of that for a spin allowed transition and for d2 configuration, the ground state terms 3F and 3P are considered.

Multiple choice

Match the columns.

 
Transitions Examples
1. d-d transition a. KMnO4
2. Ligand to metal charge transfer b. [Ti(H2O)6]+3
3. Metal to ligand charge transfer c. Ni(CO)4
4. Interligand charge transfer d. [Cu(en)2]+

  1. 1 - d, 2 - c, 3 - a, 4 - b

  2. 1 - c, 2 - b, 3 - d, 4 - a

  3. 1 - b, 2 - a, 3 - c, 4 - d

  4. 1 - b, 2 - a, 3 - d, 4 - c

  5. 1 - a, 2 - b, 3 - c, 4 - d
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

This option is correct because [Ti(H2O)6]+3, KMnO4, Ni(CO)4 and [Cu(en)2]+ are examples of d-d transition, ligand to metal charge transfer, metal to ligand charge transfer and interligand charge transfer, respectively.

Multiple choice

Assertion: The mixing of d and p orbitals does not occur in octahedral complexes which have centre of symmetry, like [Ni(NH3)6]+2 and [Co(NH3)6]+3. Reason: In these cases, the metal ligand bonds vibrate so that the ligands spend most of their time out of their centrosymmetric equilibrium position.

There are two statements, Assertion (A) and Reason (R). Consider both the statements independently and mark your answer as under:

1. A and R are both correct and R is the correct explanation of A.
2. A and R are both correct and R is not the correct explanation of A.
3. A is correct and R is incorrect.
4. A is incorrect and R is correct.
5. A and R are both incorrect.

  1. A and R are both correct and R is the correct explanation of A.

  2. A and R are both correct and R is not the correct explanation of A.

  3. A is correct and R is incorrect.

  4. A is incorrect and R is correct.

  5. A and R both are incorrect.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The mixing of d and p orbitals does not occur in octahedral complexes which have centre of symmetry, like [Ni(NH3)6]+2 and [Co(NH3)6]+3, because in these cases, the metal ligand bonds vibrate so that the ligands spend most of their time out of their centrosymmetric equilibrium position. Thus, this option is correct.

Multiple choice

Which of the following statements is/are false?

A. The spin and Laporte forbidden molar absorption coefficients are very low. B. Multiplicity forbidden transition bands are sharp while multiplicity allowed transition yields broad bands. C. Substitution in octahedral complexes, which destroys the centre of symmetry of the ligand, gives weak absorption.

  1. Only A

  2. Only B

  3. Only C

  4. A and B

  5. B and C
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Substitution in octahedral complexes, which destroys the center of symmetry of the ligand, gives higher absorption.