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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 15, Number 4
BKCSDE 15(4)
April 20, 1994 

The Kinetics of Formation and Dissociation of the 1,4,7,10,13,16-Hexaazacyclooctadecane-1,4,7,10,13,16-hexaacetate Complex of Cerium (Ⅲ)
Ki-Young Choi*, Choon Pyo Hong
The formation and dissociation rates of the 1,4,7,10,13,16-hexaazacyclooctadecane-1,4,7,10,13, 16-hexaacetic acid (H6heha)complex of Ce(Ⅲ) ion have been measured by stopped-flow and conventional spectrophotometry. Observations were made at 25.0±0.1 ℃ and at an ionic strength of 0.1 M NaClO4. The formation reaction takes place by rapid formation of an intermediate complex in which the metal ion is incompletely coordinated. In the pH range 4.1-5.2, the H3heha3- species is the kinetically active one despite of its low concentration. The exchange reaction occurring between the[Ce(heha)]3- complex and Cu2+ ion proceeds via both an acid-independent and an acid-catalyzed pathway. The buffer concentration dependence of the dissociation rate has also been investigated. The dissociation rate of the [Ce(heha)]3- complex is much faster than that of [Ce(nota)] and [Ce(dota)]-. The chelate ring size effect is discussed by comparing the rate constants to those of analogous nota and dota systems.
293 - 297
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