Equilibrium and kinetic studies of lanthanide complexes of macrocyclic polyamino carboxylates

• Published in: Inorganic chemistry 1993-03, Vol.32 (5), p.587-593
• Main Authors: Kumar, Krishan, Chang, C. Allen, Tweedle, M. F
• Format: Article
• Language: English
• Subjects: CERIUM COMPLEXES; CHELATES; CHEMICAL REACTION KINETICS; Chemistry; COMPLEXES; DISSOCIATION; EQUILIBRIUM; Exact sciences and technology; GADOLINIUM COMPLEXES; Inorganic chemistry and origins of life; INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; KINETICS; Kinetics and mechanism of reactions; LUTETIUM COMPLEXES; RARE EARTH COMPLEXES; REACTION KINETICS 400201 > Chemical & Physicochemical Properties
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/ic00057a017

The stability constants (log K[sub LnL]) of lanthanide complexes of macrocyclic polyamino carboxylates, LnL (where Ln is Ce[sup 3+], Gd[sup 3+], and Lu[sup 3+] and L is DO3A = 1,4,7,10-tetraazacyclododecane-1,3,7-triacetic acid and HP-DO3A = 10-(hydroxypropyl)-1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid), have been determined at 25.0 [plus minus] 0.1[degree]C and [mu] = 0.1 ((CH[sub 3])[sub 4]NCl). The stability constants of lanthanide complexes of DO3A increase with the decreasing ionic radii or increasing charge density of Ln[sup 3+]. For L = HP-DO3A, the stability constant of GdL is greater than that of CeL; however the stability constants of GdL and LuL are similar. The protonation constants, K[sub H] (M[sup [minus]1]), of the LnL complexes have been determined at 25.0 [plus minus] 0.1[degree]C and [mu] = 1.0 (NaCl), and the values are 18 [plus minus] 3 for Ce(DO3A), 115 [plus minus] 8 for Gd(DO3A), 11 [plus minus] 1 for Ce(HP-DO3A), and 240 [plus minus] 25 for Gd(HP-DO3A). The rates of acid-assisted dissociation of the protonated complexes, ML(H), have been measured at 25.0 [plus minus] 0.1[degree]C and [mu] = 1.0 (NaCl). Direct, k[sub d] (s[sup [minus]1]), and acid-assisted, k[sub 1] (M[sup [minus]1] s[sup [minus]1]), dissociation rate constants are k[sub d] = (1.8 [plus minus] 0.8) [times] 10[sup [minus]3] and k[sub 1] = (1.12 [plus minus] 0.04) [times] 10[sup [minus]1] for Ce(DO3A) and k[sub d] = (1.4 [plus minus] 0.2) [times] 10[sup [minus]4] and k[sub 1] = (2.00 [plus minus] 0.04) [times] 10[sup [minus]3] for Ce(HP-DO3A). The rates of dissociation of the other complexes are first order in acid at low [H[sup +]], but the rates saturate at high [H[sup +]]. 40 refs., 5 figs., 3 tabs.