Seven Europium(III) Complexes in Solution – The Importance of Reporting Data When Investigating Luminescence Spectra and Electronic Structure

Abstract Despite significant effort, the complexity of europium(III) luminescence in general – and sample composition in particular – has precluded the publication of standard spectra of specific complexes in aqueous solution. Further, low spectral resolution, weighted averages with contributions from several species, as well as poor reproduction hampers the use of literature data, with the note that high quality data from e. g. Bünzli, Latva, Carnall, Parker, Heller, Balzani and Sabatini is from the pre‐electronic era. Here, luminescence spectra of Eu.DOTA, Eu.EDTA, Eu.DPA1, Eu.DPA2. Eu.DPA3, Eu.DTPA and the Eu(III) aqua ion was determined in samples with known pH and conductivity. The ligand concentrations were varied in a buffered medium (MES) with a significant salt background. In this manner, full complexation could be ensured, while pH and ionic strength were monitored. The spectra corresponding to the complexes were extracted, and the electronic structure of the ground state 7FJ manifold was investigated and contrasted to literature data. All spectroscopic data is made available and we suggest this becomes part of the standard procedure when investigating lanthanide(III) complexes.