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POTENTIOMETRIC, CALORIMETRIC, AND SOLUTION NMR-STUDIES OF A TRIDENTATE LIGAND WHICH HAS A MARKED PREFERENCE FOR FORMATION OF BIS(LIGAND) VERSUS MONO(LIGAND) LANTHANIDE COMPLEXES AND WHICH EXHIBITS HIGH SELECTIVITY FOR HEAVIER LANTHANIDES

TitlePOTENTIOMETRIC, CALORIMETRIC, AND SOLUTION NMR-STUDIES OF A TRIDENTATE LIGAND WHICH HAS A MARKED PREFERENCE FOR FORMATION OF BIS(LIGAND) VERSUS MONO(LIGAND) LANTHANIDE COMPLEXES AND WHICH EXHIBITS HIGH SELECTIVITY FOR HEAVIER LANTHANIDES
Publication TypeJournal Article
Year of Publication1995
AuthorsCaravan, P, Hedlund, T, Liu, S, Sjoberg, S, Orvig, C
JournalJournal of the American Chemical Society
Volume117
Pagination11230-11238
Date PublishedNov
Type of ArticleArticle
ISBN Number0002-7863
KeywordsAGENTS, AMINE PHENOL LIGANDS, AQUEOUS, BIOLOGICAL-SYSTEMS, CHEMISTRY, EXCHANGE, HEPTADENTATE LIGANDS, METAL-IONS, NUCLEAR MAGNETIC-RESONANCE, probes, SHIFT-REAGENTS, WATER
Abstract

A new water-soluble N4O3 tripodal amine phenol ligand, tris(((2-hydroxy-5-sulfobenzyl)amino)ethyl)amine (H(3)TRNS) has been synthesized, and its complexation properties with six lanthanide(III) ions (Ln, Nd, Gd, Ho, Yb, Lu) have been probed. In water, the ligand coordinates in a tridentate fashion through the three phenolate oxygen atoms to give mono- and bis(ligand) complexes. The bis complexes are proposed to be 7-coordinate containing one bound water as evinced by O-17 NMR experiments on the Dy3+ complex. while the mono complexes are proposed to have a coordination number of eight or nine. The stepwise formation constants for the 1:1 and 2:1 (L:M) complexes have been measured at 25 degrees C (mu = 0.16 M NaCl) for Nd3+ (log K-1 = 6.41, log K-2 6.34), Gd3+ (log K-1 = 6.67, log K-2 = 7.69), Ho3+ (log K-1 = 7.67, log K-2 = 8.75), and Yb3+ (log K-1 = 8.53, log K-2 = 9.73). The formation constants show an increasing affinity and an unprecedented selectivity for the heavier lanthanides (beta(2(yb)) - beta(2(Nd)) = 10(5.5)). Furthermore, the stepwise stability constant for the 2:1 complex is increasingly greater than that for the 1:1 complexes of Gd3+, Ho3+, and Yb3+, while K-1 and K-2 for the 1:1 and 2:1 complexes of Nd3+ are approximately the same. Solution calorimetry shows that the selectivity for the heavier lanthanides is an enthalpic effect (Delta H-beta 2 = -45.11 (Yb) and -13.71 kJ . mol(-1) (Nd)), while the anomalous behavior in formation constants (K-2 > K-1) is predominantly entropic (Delta S-2 > Delta S-1) and is rationalized in terms of salvation of the complexes, Lanthanum(III) forms only the 1:1 complex (log K = 5.65) which precipitates from solution.

URL<Go to ISI>://A1995TE73900021