Tanabe-Sugano diagram

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Tanabe-Sugano diagrams are used in coordination chemistry to predict absorptions in the UV and visible electromagnetic spectrum of coordination compounds.

A Tanabe-Sugano diagram is a graph which plots the energy of different spectroscopic terms (on the y-axis) against the size of the ligand field (on the x-axis). The units used for each are the Racah parameter B. This choice of unit means that the diagram takes account of electron-electron repulsion effects, which an Orgel diagram cannot. It is mainly used to predict the energy of any absorption bands that are predicted but not observed in the UV/visible spectra of transition metal complexes from the energies of those that can be seen, and can also be used to predict the size of the ligand field necessary to cause high-spin to low-spin transitions.