SHARP-LINE ELECTRONIC-SPECTRA AND METAL-LIGAND GEOMETRY

The narrow intraconfigurational lines in the electronic spectra of transition metal complexes can, unlike broad bands, be assigned to single electronic transitions. The positions of, and especially the splittings within, these lines are strongly influenced by the angular positions and orientations of the ligands. The angular overlap model (AOM) is well suited to treat the exact geometry as part of the ligand field potential. It is possible in some instances to deduce particular bond angles by analysis of the electronic spectrum. It is suggested that when AOM parameters are deduced from spectral data, the ligand geometry be explicitly included, either directly from an X-ray crystal structure, if available, or from an approximate method, such as a molecular mechanics calculation. This ought to insure the maximum transferability of parameters for a particular ligand in different complexes, and for a particular coordinating group in different ligands.