Question 20.9: Draw a crystal field orbital energy-level diagram, and predi......
Draw a crystal field orbital energy-level diagram, and predict the number of unpaired electrons for each of the following complexes:
STRATEGY
All three complexes are octahedral, so the energy-level diagrams will show three lower-energy and two higher-energy d orbitals. For complexes, the electrons occupy the orbitals in accord with Hund’s rule so as to give the maximum number of unpaired electrons. For complexes, the orbital occupancy and number of unpaired electrons depend on the position of the ligand in the spectrochemical series.
(a) has three unpaired electrons. In the complex, they occupy the lower-energy set of d orbitals as shown below.
(b) can have a high-spin or a low-spin configuration. Because is a strong-field ligand, all four d electrons go into the lower-energy d orbitals. The complex is low-spin, with two unpaired electrons.
(c) has a high-spin configuration with three unpaired electrons because is a weak-field ligand.
In the following orbital energy-level diagrams, the relative values of the crystal field splitting Δ agree with the positions of the ligands in the spectrochemical series :
