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Question

Among the following statements A-D, the incorrect ones are:

A. Octahedral Co(III) complexes with strong field ligands have high magnetic moments.

B. When Δo<P, the d- electron configuration of Co(III) in an octahedral complex is t42g,e2g.

C. Wavelength of light absorbed by [Co(en)3]3+is lower than that of [CoF6]3.

D. If the Δ0 for an octahedral complex of Co(III) is 18000cm1, the Δt for its tetrahedral complex with the same ligand will be 16000cm1 .


A

B and C only

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B

A and B only

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C

A and D only

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D

C and D only

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Solution

The correct option is C

A and D only


The explanation for the correct option:

(C) A and D only

Statement A:

  1. Octahedral Co(III) complexes with strong field ligands have high magnetic moments.
  2. Crystal field splitting of octahedral Co(III) complexes with strong field ligands can be shown as follows:
  3. From the splitting it can be observed that Octahedral Co(III) complexes does not have any unpaired electrons hence, the magnetic moment for these complexes is 0BM.
  4. Hence, statement A is incorrect.

Statement D:

  1. If the Δ0 for an octahedral complex of Co(III) is 18000cm1, the Δt for its tetrahedral complex with the same ligand will be 16000cm1 .
  2. The formula for calculating Δt using the value of Δ0 is as follows: t=490
  3. Putting the value of Δ0 to calculate Δt: t=49×18000t=8000cm-1
  4. So the Δt for tetrahedral complex is 8000cm-1.
  5. Hence, statement D is incorrect.

Explanation for incorrect options:

(A) B and C only

Statement B:

  1. When Δo<P, the d- electron configuration of Co(III) in an octahedral complex is t42g,e2g.
  2. The crystal field splitting of Co(III) in an octahedral complex when Δo<P can be shown as follows:
  3. From the splitting it is clear that the number of electrons in t2gandeg orbitals are four and two respectively.
  4. Hence, statement B is correct.

Statement C:

  1. Wavelength of light absorbed by [Co(en)3]3+is lower than that of [CoF6]3.
  2. Ethylenediamine is a strong ligand but fluorine is a weak ligand so, more energy is absorbed by [Co(en)3]3+ complex than [CoF6]3 complex.
  3. Thus, the wavelength of light absorbed is more for [Co(en)3]3+than[CoF6]3.
  4. Hence, statement C is correct.

(B) A and B only

It can be observed from the above discussion that statement A is incorrect and statement B is correct.

(D) C and D only

It can be observed from the above discussion that statement D is incorrect and statement C is correct.

Hence, option C is correct, statement A and D are incorrect.


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