Potentiometry and NMR Studies of 1,5,9-Triazacyclododecane-N,N′,N″-triacetic Acid and Its Metal Ion Complexes

E. Cortes, S. Brucher, C. F G C Geraldes, A. D. Sherry

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A new chelating macrocycle, 1,5,9-triazacyclododecane-N,N′,N″-triacetic acid (DOTRA), has been synthesized, and its complexes with Zn2+, Cd2+, Ca2+, Mg2+, and Mn2+ have been examined by potentiometry and NMR spectroscopy. The first protonation constant of the free ligand (log K1 = 12.8) was determined spectrophotometrically, while the remaining were evaluated from potentiometric data (log K2 = 7.55, log K3 = 3.65, log K4 = 2.1). DOTRA forms complexes with Mn2+, Mg2+, and Ca2+ rather slowly but reacts much more rapidly with Zn2+ and Cd2+. As reported previously for the nine-membered-ring triaza analogue NOTA, DOTRA also forms a more stable complex with Mg2+ than with Ca2+ (log Kst = 7.1 versus 6.0). High-resolution NMR spectra of the Zn2+, Cd2+, and Mg2+ complexes (log Kst = 19.0, 15.7, and 7.1, respectively) indicate the three six-membered chelate rings are symmetrical and quite rigid in aqueous solution, as evidenced by nonequivalence of all six chelate ring protons.

Original languageEnglish (US)
Pages (from-to)5-9
Number of pages5
JournalInorganic Chemistry
Issue number1
StatePublished - Jan 1 1990


ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Inorganic Chemistry

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