Electronic Structure of Ferric Iron Octahedrally Coordinated to Oxygen

A FERRIC ion coordinated to an octahedron of oxide ions may be considered the basic polyhedral unit of Fe2O3 (haematite) and an important unit in Ca3Fe2Si3O12 (andradite garnet), Fe3O4 (magnetite) and other silicate and oxide minerals. A knowledge of the electronic structure of this unit is of considerable interest in mineralogy and solid state science. In recent years a great deal of information on the electronic structure of minerals has been obtained from the study of their spectral properties. We report here results of molecular quantum mechanical calculations on an FeO69- unit and compare them with experimental data from X-ray emission, X-ray photoelectron and optical spectroscopies. The agreement found between experimental and calculated spectral transition energies establishes the validity of the calculation and furthermore clarifies the interpretation of the spectral data.