Question

Analysing Tanabe-Sugano diagrams it's evident that some of the lines are pretty parallels to that of the ground field whilst others are inclinated or have some curvature.

I know what's the effect on the line width of the spectra, but I'd like to have an explanation on why we have so different behaviours.

The fact that in Orgel diagrams some lines are straight and others have curvature is related to this?

Answer 1

Tanabe-Sugano diagrams display electronic transitions within coordination compounds' d-orbitals, reflecting crystal field splitting. Parallel lines indicate constant energy transitions, while curves represent varying energy states affected by ligand field strength. Orgel diagrams provide a simpler view of these phenomena for first-row transition metals, but the concepts are closely related.

Step-by-step explanation:

The behavior observed in Tanabe-Sugano diagrams can be explained through electronic transitions within the d-orbitals of a coordination compound. These transitions are subject to crystal field splitting, which is influenced by the geometric arrangement of ligands around the metal ion.

In a Tanabe-Sugano diagram, which is used for more complex transition metal ions beyond the first-row transition metals, the energy levels and transitions between them reveal differences in behavior and curvature, corresponding to various spin states and electron configurations.

The parallel lines indicate transitions that do not change in energy with increasing crystal field strength, such as transitions between states of the same spin multiplicity.

Lines that are not parallel reflect changes in energy due to stabilization or destabilization of particular electronic states as the crystal field strength varies. The curvature notable in some transitions in these diagrams results from the varying degree to which the energy levels are affected by the strength of the ligand's field.

The Orgel diagrams, on the other hand, are relevant for first-row transition metal ions and depict the simpler case of crystal field splitting in an octahedral environment. The lines or curves in Orgel diagrams visualize the effect of the crystal field splitting on the degenerate d-orbitals.

The behavior shown in Orgel diagrams is indeed analogous to that in Tanabe-Sugano diagrams; the former just represents a simpler subset of the phenomena.

Spectra, whether they are emission or absorption, are influenced by the transitions represented in these diagrams. The width and complexity of spectral lines are affected by factors such as spin-orbit coupling and the presence of a magnetic or electric field, which can cause additional splittings known as fine structure.