Jean-Claude Bunzli - Lanthanide chelates based on diethylenetriamine fitted with O-benzoic acid pendant arms

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  Publication Details (including relevant citation   information):

  Imbert,D., Fatin-Rouge,N., Bunzli,J.C.G. European Journal of   Inorganic Chemistry 2003 (7) 1332-1339

  Abstract: A new polycarboxylate ligand H5L has   been synthesized by the attachment of five benzoate subunits onto   a diethylenetriamine framework. Seven pK(a) 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 Ln(III) 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 logK(11) = 5.3(2),   6.6(1), 6.5(1) and 7.2(3) for La, Eu, Tb and Lu, respectively. In   the case of Tb-III, the stability constants for [Tb(HL)](-) and   [Tb(H2L)] are logbeta(111) = 22.0(2) and logbeta(121) = 29.8(1),   giving a pTb of 10.0. the pH range 4-7, more than 90% of the   Tb-III ions are in the form of the neutral species [Tb(H2L)].   Lifetime determinations of the Eu(D-5(0)) and Tb(D-5(4)) 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 Ln(III). 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: phiabs = 10.3%), while the luminescence of Eu-III   is only poorly sensitised (phi(abs) = 1.5%)

  Address (URL): J INORG CHEM