Among the following complexes the one which shows Zero crystal field s...
Explanation:
Crystal field stabilization energy (CFSE) is the energy required to pair up electrons in the d-orbitals of a transition metal ion in a crystal field.
The CFSE of a complex depends on the number of electrons in the d-orbitals of the central metal ion, the number of ligands surrounding the metal ion, and the nature of the ligands.
In general, the CFSE increases with an increase in the number of ligands surrounding the metal ion and a decrease in the number of d-electrons on the metal ion.
The CFSE of the complexes can be calculated using the Tanabe-Sugano diagram.
Among the given complexes, [Fe(H2O)6]3+ shows zero CFSE.
Reason:
The electronic configuration of Fe3+ ion is 3d5. In [Fe(H2O)6]3+, all the six water ligands are weak field ligands. Hence, they do not split the d-orbitals of Fe3+ ion.
As a result, all the five d-electrons of Fe3+ ion occupy the d-orbitals in an octahedral field. Since there is no pairing of electrons, the CFSE of [Fe(H2O)6]3+ is zero.
On the other hand, [Co(H2O)6]2+ and [Co(H2O)6]3+ have 3d7 and 3d6 electronic configurations, respectively. In both cases, the water ligands are weak field ligands and hence do not split the d-orbitals of Co2+ and Co3+ ions.
However, due to the presence of unpaired electrons in the d-orbitals, there is a non-zero CFSE for these complexes.
Similarly, Mn3+ ion has a 3d4 electronic configuration and the water ligands are weak field ligands. Hence, [Mn(H2O)6]3+ also has a non-zero CFSE.
Conclusion:
Thus, the correct option is D, i.e., [Fe(H2O)6]3+ shows zero CFSE.
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