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Szilagyi, E ; Toth, E ; Kovacs, Z ; Platzek, J ; Raduchel, B ; Brucher, E

Equilibria and formation kinetics of some cyclen derivative complexes of lanthanides

Inorganica Chimica Acta 298 (2) 226-234

par Administrateur - publié le

Abstract :

The kinetics of the formation reactions between the lanthanide(III) ions Ce3+, Eu3+ and Yb3+ and four cyclen derivative ligands, DO3A-B, DO3A-ME, DO2A and DO2A-2B, were studied by spectrophotometry and a stopped-flow method at 25 degrees C in 1.0 M KCl solutions. The reactions were found to be of first order, which was interpreted in terms of the formation of a diprotonated intermediate, Ln(H2L)(+). The formation of products occurs via deprotonation and rearrangement of the intermediate, characterised by the rate constant, ii,. The rate law obtained, k(r) = k(OH)[OH ], is similar to those obtained for the formation reactions of DOTA and DOTA derivative complexes. The rate constants, k(OH), decrease with decrease in the number of charged carboxylate functional groups in the ligandsl the lowest rates were found for the formation of the DO2A complexes.