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Research has been conducted on europium complexation with tridentate ligands. The use of electrospray mass spectrometry in investigating this complexation is described.

The 2,6-bis(5,6-dialkyl-1,2,4-triazin-3-yl)pyridines (DATPs) belong to a new family of extracting agents recently developed in the framework of nuclear fuel reprocessing. These molecules exhibit exceptional properties to separate actinides(III) from lanthanides(III) in nitric acid solutions. In a previous work, the use of electrospray ionization mass spectrometry (ESI-MS) provided data such as stoichiometries and conditional stability constants of various DATP complexes with europium and evidenced the unusual capability of DiPTP [bis(di-iso-propyltriazinyl)pyridine] ligand to form 1:3 complexes in nitric acid solution. This latter result has then been further investigated by considering DiPTP complexation features with the complete lanthanide family. Moreover, a complementary study of equilibria in solution with a non intrusive technique such as time-resolved laser-induced luminescence (TRLIL) seemed quite promising to determine thermochemical data such as enthalpy and entropy variations associated with the complexation reaction between Eu(III) and DiPTP. Furthermore, this TRLIL study may also allow ensuring that the observations made on mass spectra actually reflected the equilibrium in solution and not an intermediate state between liquid phase and gaseous phase. The investigation of europium(III) complexation with DiPTP by TRLIL described in this paper first led to highlight the exclusive formation of a 1:3 complex between europium(III) and the DiPTP ligand, specificity already pointed out by ESI-MS. Two different calculation methods, using either luminescence spectra and luminescence decay curves, have then been used to measure the conditional stability constant of the [Eu(DiPTP)3]3+ complex. Both methods gave similar results (log β3app = 14.3 ± 0.6 at pH 2.8) in good agreement with the one previously reported in ESI-MS studies (log β3app = 14.0 ± 0.6 at pH 2.8). Moreover, while considering the influence of temperature on the value of the stability constant, it was possible to estimate the enthalpy (δHβ3 = -29 ± 3 kJ mol-1 at pH 2.8) and entropy variations (δSβ3 = 173 ± 10 J K-1 mol-1 at pH 2.8) associated with the [Eu(DiPTP)3]3+ complex formation. [ABSTRACT FROM AUTHOR]

The water soluble polyazamacrocyclic ligand, 3,6,9,15-tetraazabicyclo[9.3.1]pentadeca-1(15),11,13-triene-3,6,9-triacetic acid (111Py12N4) has been synthesized and found to be an effective antenna molecule for europium luminescence. When bound to Eu(III), excitation at the absorption band of the 111Py12N4 ligand (264 nm) leads to the well-known structured emission spectrum of the Eu(III) ion with a large Stockes shift (>250 nm). UV-light induced Eu(III) luminescence resulting from a through-space energy transfer allowed the determination of a 1:1 stoechiometry of the Eu(III) complex and the determination of the corresponding stability constant (log Ktherm=20.9). The luminescence lifetimes, the number of water molecules coordinated to the metal as well as the overall quantum yields were evaluated. [Copyright &y& Elsevier]

Abstract: The synthesis of the first example of a new class of tetradentate reagents for the efficient separation of americium(III) and europium(III) is reported together with the structure of the complex formed with europium(III). [Copyright &y& Elsevier]