Complexation of europium(III) by hydroxybenzoic acids: A time-resolved luminescence spectroscopy study

Abstract

Complexation of Eu(III) by two hydroxybenzoic acids, namely p-hydroxybenzoic acid (4-dihydroxybenzoic, HPhbH), and protocatechuic acid (3,4-dihydroxybenzoic, HProtoH 2 ), is studied by time-resolved luminescence spectroscopy (TRLS) in mildly acidic solution.Comparable formation constants are determined at 0.1 mol.L -1 NaCl for EuPhbH 2+log 10 β°(EuPhbH 2+ ) = 2.18  0.09 (1)and 0.01 mol.L -1 NaCl for EuProtoH 2 2+log 10 β°(EuProtoH 2 2+ ) = 2.72  0.07 (1). The stoichiometry and carboxylate complexation of the EuProtoH 2 2+ complex is ascertained by varying both pH and ligand concentration. The luminescence decay time of EuPhbH 2+ (τ = 107 ± 5 µs) is comparable with that of Eu(H 2 O) n 3+(τ = 110 ± 3 µs), suggesting that luminescence quenching processes compensate the expected increase in decay time due to the dehydration associated with complexation. For EuProtoH 2 2+ , the luminescence decay time is even shorter (τ = 20 ± 5 µs), evidencing intricate quenching processes.

Influence of adipic acid on the speciation of Eu(III): Review of thermodynamic data in NaCl and NaClO4 media, and a new determination of Eu-adipate complexation constant in 0.5 mol·kgw−1 NaClO4 medium by time-resolved luminescence spectroscopy

“…The TRLS experimental set-up is slightly modified compared to the one already described elsewhere [19,[21][22][23][36][37][38]. It is including a 355 nm tripled neodymium-doped yttrium aluminium garnet (Nd:YAG) laser (Surelite, Continuum) providing ca.…”

“…The luminescence decay times are obtained as described elsewhere [19,21,37], fitting the decay to the following equation.…”

“…As ions from a dicarboxylic acid, adipate ions are able to complex trivalent f-transition elements [12] such as Eu(III) [13] -analogue of 5f actinides(III) such as Cm(III) and Am(III) for the complexation by oxygen containing molecules [14]. Eu(III) is showing interesting luminescent properties that makes it suitable for both complexation studies and chemical environment probing by time-resolved luminescence spectroscopy (TRLS), [13,[15][16][17][18][19][20] including complex organic mixtures [21][22][23]. The assessment of the extent of complex formation by the organic ligands identified in HDPs requires thermodynamic data both on protonation constants for these ligands, as well as on complexation with radionuclides, including the account of ionic strength in the case of cemented waste packages.…”

Electrochemical behaviours of Eu(III)/E(II) and Ce(IV)/Ce(III) in H3PO4-H2O media : solvation and complexation reactions

“…Various phosphoric acid solutions are produced from phosphate ores before fertilizer-grade phosphoric acid using an industrial processing and contain valuable quantities of rare earths elements; hence, it is considered as secondary source for rare-earth elements [4][5][6]. Only a small proportion of REE deposits are of sufficient size and concentration that they can be exploited economically using existing technology [7]. Rare earth elements exist in phosphorite deposits, which should be extracted using various methods [8][9][10][11].…”

Crystal Structures of New Lanthanide Hydroxybenzoates and Different Roles of LMCT State in the Excitation Energy Transfer to Eu3+ Ions

“…Eu 3+ ion is a good model for studies of complexation between heavy metal ions and humic substances, in particular, hydroxybenzoic acids, with the help of luminescence spectroscopy . Thermodynamic parameters for complexation of europium lanthanides by hydroxybenzoic acids in an aqueous solution were determined and the charge distributions on the atoms of benzoate ligands were calculated …”