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Lanthanide Chelates Based on Diethylenetriamine Fitted with O ‐Benzoic Acid Pendant Arms
Author(s) -
Imbert Daniel,
FatinRouge Nicolas,
Bünzli JeanClaude G.
Publication year - 2003
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.200390173
Subject(s) - chemistry , diethylenetriamine , lanthanide , ligand (biochemistry) , benzoic acid , aqueous solution , chelation , stability constants of complexes , amine gas treating , molecule , equilibrium constant , medicinal chemistry , ion , nuclear chemistry , inorganic chemistry , crystallography , organic chemistry , biochemistry , receptor
A new polycarboxylate ligand H 5 L has been synthesized by the attachment of five benzoate subunits onto a diethylenetriamine framework. Seven p K 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 H 5 L 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 log K 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(H 2 L)] are logβ 111 = 22.0(2) and logβ 121 = 29.8(1), giving a pTb of 10.0. In the pH range 4−7, more than 90% of the Tb III ions are in the form of the neutral species [Tb(H 2 L)]. Lifetime determinations of the Eu( 5 D 0 ) and Tb( 5 D 4 ) excited levels in both H 2 O and D 2 O 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: φ abs = 10.3%), while the luminescence of Eu III is only poorly sensitised (φ abs = 1.5%). (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)