Abstract
The solution phase coordination chemistry assoicated with the 1:1 complexes of lanthanide ions with triethylenetetraaminehexaacetic acid (TTHA) has been studied by spectroscopic means. It was found that in the pH region of 3 to 7.5, the partially protonated Ln(TTHA) complexes exist as oligomeric species. A well defined polynuclear species has been found to exist between pH 4 and 6, and this characterized by an association constant of 125. Between pH 6 and 8, the oligomeric species apparently dissociate, yielding monomeric lanthanide TTHA complexes above pH 8.

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