Question:medium

Among the following complexes the one which shows zero crystal field stabilization energy (CFSE) is:

Updated On: Apr 20, 2026
  • [Fe(H2O)6]3+
  • [Co(H2O)6]2+
  • [Co(H2O)6]3+
  • [Mn(H2O)6]3+
Show Solution

The Correct Option is A

Solution and Explanation

The question requires determining which of the given complexes has zero Crystal Field Stabilization Energy (CFSE). Let's analyze each complex to identify the correct answer.

1. [Fe(H2O)6]3+

  • Iron in this complex has an oxidation state of +3, which makes it Fe3+. The electronic configuration of Fe3+ is [Ar] 3d5 4s0.
  • In an octahedral field provided by water ligands (which are weak field ligands), the 3d orbitals of the Fe3+ ion split into t2g and eg sets.
  • Since water is a weak field ligand, the splitting is not large enough to pair the electrons, and all five d-electrons remain unpaired, occupying the t2g and eg orbitals equally.
  • This results in no net stabilization from the crystal field splitting, and thus, the CFSE is zero.

2. [Co(H2O)6]2+

  • Cobalt in this complex is in the +2 oxidation state, Co2+, with an electronic configuration of [Ar] 3d7.
  • With water as a weak field ligand, the d-orbitals will split, and electrons will be distributed among the t2g and eg orbitals.
  • In this case, CFSE is not zero as there is some stabilization due to partial filling of the t2g level.

3. [Co(H2O)6]3+

  • With Co3+, we have an oxidation state of +3, having the configuration [Ar] 3d6.
  • This complex will also have partial stabilization due to uneven filling of the t2g and eg orbitals, leading to non-zero CFSE.

4. [Mn(H2O)6]3+

  • Manganese in the +3 oxidation state has a configuration of [Ar] 3d4.
  • With weak field ligands like water, there will be a splitting, resulting in stabilization due to asymmetric electron distribution.

Based on the above analysis, the complex with zero CFSE is [Fe(H2O)6]3+, as all its d-electrons are unpaired and evenly distributed between t2g and eg orbitals, conferring no net crystal field stabilization.

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