CORRELATION OF MOLECULAR STRUCTURE WITH FLUORESCENCE SPECTRA IN RARE EARTH CHELATES .I. INTERNAL SPLITTING IN TETRAETHYLAMMONIUM TETRAKIS(DIBENZOYLMETHIDO)EUROPATE(3)

The internal Stark splitting in the emission spectrum of tetraethylammonium tetrakis-(dibenzoylmethido)europate(III) in microcrystals at 77°K was analyzed in detail treating the ligand field as a perturbation on the free ion levels. The complete equivalence between crystalline field and a molecular (ligand) field in chelates with respect to the splitting of the intra-4f levels allows the use of equivalent operator techniques in the calculation of ligand field parameters. These parameters were derived from the splitting in the 7F1 and 7F2 levels of the Eu3+ ion without assuming a known molecular geometry, and their values establish the configuration of the emitting species. In addition, the ligand field parameters are used to calculate interatomic distances and bond angles. The method developed for deriving and verifying the geometrical arrangement, interatomic distances, and bond angles from fluorescence spectra proves to be a powerful tool.