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Question:

Among the following complexes, the one which shows zero crystal field stabilization energy (CFSE)?

[Co(H2O)6]3+

[Co(H2O)6]2+

[Ni(H2O)6]3+

[Fe(H2O)6]3+

Solution:

For the complex [Fe(H2O)6]3+, the outer electronic configuration of Fe3+ is 3d5 (t2g3 eg2). In an octahedral field, the energy of the t2g orbitals is lowered by -0.4Δo, and the energy of the eg orbitals is raised by 0.6Δo. The CFSE is calculated as follows:

CFSE = (number of electrons in t2g orbitals × -0.4Δo) + (number of electrons in eg orbitals × 0.6Δo)

For [Fe(H2O)6]3+, we have 3 electrons in t2g and 2 electrons in eg orbitals.

CFSE = (3 × -0.4Δo) + (2 × 0.6Δo) = -1.2Δo + 1.2Δo = 0

Therefore, [Fe(H2O)6]3+ shows zero crystal field stabilization energy (CFSE).