Spectroscopic investigations of complexes between Eu(III) and aromatic carboxylic ligands

In order to obtain information on the number and symmetry of the different E

High-resolution steady-state and time-resolved luminescence studies on the complexes of Eu(III) with aromatic or aliphatic carboxylic acids

Eu(III) luminescence spectroscopy, both in the steady-state and the time-resolved mode, is an appropriate technique to study the properties of complexes between heavy metal ions and humic substances (HS), which play a key role in the distribution of metal species in the environment. Unfortunately, room temperature luminescence spectra of Eu(III) complexes with aromatic and aliphatic carboxylic acids - model compounds of HS binding sites - are too broad to fully exploit their potential analytical information content. It is shown that under cryogenic conditions fluorescence-line-narrowing (FLN) is achieved, and the highly resolved spectra provide detailed information on the complexes. Ten model ligands were investigated. Total luminescence spectra (TLS) were recorded, using th

Metal Binding by Humic Substances - Characterization by High-Resolution Lanthanoide Ion Probe Spectroscopy (HR-LIPS)

Abstract In ultra-low-temperature experiments at 4.7 K the luminescence of Eu(III) bound to different hydroxy- and methoxybenzoic acids and to humic substances (HS) was investigated. The benzoic acid derivatives were used as simple model compounds for common metal-binding structures in HS. The Eu(III) luminescence was directly excited by means of a pulsed dye laser, scanning through the 5D0 ← 7F0 transition of Eu(III) and subsequently high-resolution total luminescence spectra (TLS) were recorded. Based on the thorough analysis of the high-resolution TLS conclusions were drawn with respect to the number of different complexes formed and to the symmetry of the complexes. The crystal-field strength parameter Nν (B2q) was dependent on the electrostatic forces induced by the ligands as well as on the symmetry of the complexes. The formation of thermodynamically stable complexes was found to be slow even for small model ligands such as 2-hydroxybenzoic acid. Comparison between the model compounds and HS clearly revealed that the carboxylate group is the dominant binding site in HS. Indices for the formation of chelates, e. g. similar to 2-hydroxybenzoic acid, were not found for HS</jats:p