[killacam2]

A little help?

Consider two Ni(II) complexes, [NiX6]4- and [NiY6]4-. If DELTAoct for both complexes is the same but B([NiX6]4-) = 2B([NiY6]4-), how would the transition energies of the spin-allowed d-d bands differ?

Where B is the Ratio of B/Bo (the racah splitting parameters)

[shengoc]

since both are Ni(II), then any difference would be due to the difference in ligands. See whether X, Y where they are in the spectrochemical series, ie from the beta value.

ie this question is asking you to describe how Nephelauxetic Effect arises from difference in ligands.

[killacam2]

Are you sure? I think it is related to Tanabe Sugano diagrams?

Here is my rationale in solving this. The second complex has a ß which is half of that of the first complex, hence it is smaller. A smaller ß must mean that in the complex, it has a smaller B value. If ∆oct is the same and B is smaller in the second case, then the energy transition must be smaller also. For example;

If an observed transition energy for a complex occurs at 30∆oct/B and is observed to have the energy 30E/B, and the following values are true: ∆oct = 15000, B = 600. Our energy will therefore be 30 x 600 = 18000.

However, if in our second case, all values remain the same, but B = 300, our energy will therefore be 30 x 300 = 9000. Hence, a smaller ß value will lead to a lower energy transition.

Is that right? Or is it to do with the covalent character of the complex and the electron repulsion?