Question:

Given below are two statements, one is labelled as Assertion A and the other is labelled as Reason R 
Assertion: Magnetic moment of [Fe(H2O)6]3+ is 5.92 BM and that of [Fe(CN)6]3– is 1.73 BM 
Reason: Oxidation state of Fe in both the complexes is +3. 
In the light of the above statements, choose the correct answer from the options given below

Updated On: Jan 16, 2025
  • Both Assertion and Reason are correct and Reason is the correct explanation of Assertion

  • Both Assertion and Reason are correct but Reason is not the correct explanation of Assertion

  • Reason is correct but Assertion is not correct

  • Reason is incorrect but Reason is correct

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The Correct Option is A

Solution and Explanation

  • Oxidation State of Fe:
    • In both complexes, the oxidation state of Fe is +3. The electronic configuration of Fe3+ is [Ar] 3d5.
  • Magnetic Moment of [Fe(H2O)6]3+:
    • Water is a weak field ligand, so it does not cause significant splitting of the d-orbitals (according to crystal field theory). 
    • As a result, all five d-electrons in Fe3+ remain unpaired.
    • The magnetic moment is given by the formula: μ = √n(n + 2), where n is the number of unpaired electrons.
    • For 5 unpaired electrons: μ = √5(5 + 2) = √35 = 5.92 BM.
  • Magnetic Moment of [Fe(CN)6]3–:
    • Cyanide (CN) is a strong field ligand, which causes significant splitting of the d-orbitals.
    • This leads to the pairing of all five d-electrons in Fe3+, resulting in no unpaired electrons.
    • For 1 unpaired electron: μ = √1(1 + 2) = √3 = 1.73 BM.

Conclusion:

Both the Assertion and the Reason are correct. The Reason correctly explains the differences in the magnetic moments due to the ligand field strength in the two complexes.

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Concepts Used:

Coordination Compounds

A coordination compound holds a central metal atom or ion surrounded by various oppositely charged ions or neutral molecules. These molecules or ions are re-bonded to the metal atom or ion by a coordinate bond.

Coordination entity:

A coordination entity composes of a central metal atom or ion bonded to a fixed number of ions or molecules.

Ligands:

A molecule, ion, or group which is bonded to the metal atom or ion in a complex or coordination compound by a coordinate bond is commonly called a ligand. It may be either neutral, positively, or negatively charged.