Multiple choice

The CFSE for octahedral complexes of Fe3+ in a weak field and strong field ligand systems are ____________ respectively.

    • 4Dq, - 20 Dq

  2. 0, - 20 Dq
    • 4Dq, - 20 Dq+2P
    • 12Dq, - 20 Dq+2P

  5. 0, - 20 Dq+2P
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E Correct answer
Explanation

In a weak field ligand system, the electron filling of splitting of d-orbital corresponds to Hund’s rule, followed by pairing. In strong field ligand system, the electron filling of splitting of d-orbital corresponds to pairing at initial stage. For Fe3+ electronic configuration is d5. For d5 in weak field ligand system, CFSE = 3 (- 4) + 2 (6) = - 12 + 12 = 0 Dq (All electrons is unpaired, 3 in t2g and 2 in eg) For d5 in strong field ligand system, CFSE = 5 (- 4) + 0 = - 20 Dq + 2P
(two paired electrons and one electron is unpaired in t2g and 0 electron in eg orbital) Hence, the CFSE for octahedral complexes of Fe3+ in a weak field and strong field ligand systems are 0 and -20 Dq+2P respectively.

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