569642-39-3Relevant academic research and scientific papers
Lanthanide chelates based on diethylenetriamine fitted with O-benzoic acid pendant arms
Imbert, Daniel,Fatin-Rouge, Nicolas,Buenzli, Jean-Claude G.
, p. 1332 - 1339 (2003)
A new polycarboxylate ligand H5L has been synthesized by the attachment of five benzoate subunits onto a diethylenetriamine framework. Seven pKα values have been determined by potentiometry, spectrophotometry and NMR spectroscopy as 1.9(2), 2.8(2), 3.87(5), 4.58(6), 4.87(6), 9.19(6) and 11.68(5), the first four corresponding to the carboxylic functions and the last three to amine sites. The interaction between H5L and LnIII ions in dilute aqueous solution has been examined by UV/Vis absorption and emission spectrometries, and has been found to result in monometallic complexes that are moderately stable in the pH range 3.7-7.5. Conditional stability constants at pH 5.3 are logK11 = 5.3(2), 6.6(1), 6.5(1) and 7.2(3) for La, Eu, Tb and Lu, respectively. In the case of TbIII, the stability constants for [Tb(HL)]- and [Tb(H2L)] are logβ111 = 22.0(2) and logβ121 = 29.8(1), giving a pTb of 10.0. In the pH range 4-7, more than 90% of the TbIII ions are in the form of the neutral species [Tb(H2L)]. Lifetime determinations of the Eu(5D0) and Tb(5D4) excited levels in both H2O and D2O at pH 5.3 indicate 4.8 ± 0.5 (Eu) and 4.5 ± 0.5 (Tb) water molecules being bound in the inner coordination sphere of the LnIII. The triplet state of the ligand in water lies at around 26000 cm-1, resulting in a sizeable sensitisation of the Tb-centred luminescence (absolute quantum yield: φabs = 10.3%), while the luminescence of EuIII is only poorly sensitised (φabs = 1.5%). Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003.
