Ligand field splitting introduced

When Cr202 is introduced as an impurity into the a-Al202 lattice, as occurs in the semiprecious mineral mby, the color is red rather than the normal green. This color anomaly is the result of ligand field splitting of the Cr(III) ion (51,52). Chromium (ITT) also colors other minerals (53). 

In discussing spectra, it will be particularly useful to be able to relate the electronic spectra of transition metal complexes to the ligand field splitting, A for octahedral complexes. To do this it will be necessary to introduce two special types of diagrams, correlation diagrams and Tanabe-Sugano diagrams. 

To assign the bands and to calculate the ligand field splittings certain simplifications are introduced. 

As the ligand-field splitting of the d orbitals in lower symmetry complexes lead to lower degeneracies and so a need for more parameters to describe them (see Table 6.6), so the d-d transitions of complexes of other than octahedral and tetrahedral geometries can only be discussed by introducing these parameters. For square planar complexes, for instance, two additional parameters must be introduced. 

The spectra of complexes containing the lanthanide metals cannot be reproduced accurately without the inclusion of spin-orbit effects. These effects are known to be as large as the ligand field effects in splitting the states that are predominantly d or/in nature. Initial attempts to include the lanthanides in the INDO/S model have, however, been made, and a spin-orbit option has been introduced into the model.A full spectroscopic calculation including spin-orbit corrections appears in Table 11 for TiO. Notice in this case how the spin-orbit splitting factor A has been used to help assign the <1) and b n transitions. 

---