Beziehungen zwischen Lumineszenzspektrum und Struktur von Seltenerdkomplexen. III. Zur Existenz unterschiedlicher Polyedertypen bei Alkalitetrakis(dibenzoylmethanato)europat(III)-Komplexen

The luminescence spectra of alkali tetrakis(dibenzoylmethido)europate(III) complexes in the crystalline state at 77°K have been measured in the spectral region 510–640 nm. The spectra show the existence of different modifications of these compounds. The spectra of the β-forms are consistent with a site symmetry D₂ at the Eu(III) ion, the spectra of the corresponding α-forms with a site symmetry D₄. A conversion from the β-form into the α-form on heating is observed in some cases. The conversion involves a change from dodecahedral into antiprismatic coordination around the Eu(III) ion.