Analysis of fluorescence spectra of rare-earth chelates. Part IV. Effects of para-bromo-substitution on internal stark splitting and molecular geometry of tetrakis(dibenzoylmethido)europate(III)

Abstract

The fluorescence spectrum of tetraethylammonium tetrakis(di-p-bromodibenzoylmethido)europate(III) was analysed in detail by treating the ligand field as a perturbation on the free-ion levels. From the splitting in the ⁷F₁ and ⁷F₂ levels of Eu³⁺ ion the ligand-field parameters were calculated without assuming a known molecular geometry and the structure suggested by these parameters is discussed. Comparison of parameter values of the p-bromo-substituted chelate with those of the unsubstituted dibenzoylmethide indicates that a substantial change in molecular geometry has occurred on replacing the para-H atoms with Br. Further, the experimentally derived parameters allowed calculation of interatomic distances and bond angles and suggested an increase in charge density in the vicinity of the lanthanide ion on p-bromo-substitution.