Journal of alloys and compounds vol:323 pages:828-832
Mixed complexation of the lanthanide(III) chelates of the 1,7-disubstituted tetraazocyclododccane macrocycles DO2A and DO2P with phosphate, acetate and fluoride anions was studied in aqueous solutions using high resolution H-1 and P-31 NMR spectroscopy. The [La(DO2A)(H2O)(2-3)](+) and [Ce(DO2A)(H2O)(2-3)](+) chelates readily decompose in aqueous solutions containing phosphate anions. [Nd(DO2A)(H2O)(2-3)](+) and [Eu(DO2A)(H2O)(2-3)](+) chelates remain stable in an acetate environment. Association constants for the 1:1 adduct were obtained via 'H NMR titrations. In a fluoride environment, [La(DO2A)(H2O)(2-3)](+) was found to be unstable, in contrast to [Eu(DO2A)(H2O)(2-3)](+), for which the association constant for the 1:1 adduct was calculated. Chelate formation, as well as mixed complexation with fluoride and phosphate was studied for [Eu(DO2P)(H2O)(2-3)](-). The P-31 chemical shifts of [Eu(DO2P)(H2O)(2-3)](-) indicate that the DO2P macrocycle forms an 'in-cage' complex with binding through all four nitrogens. The [Eu(DO2P)(H2O)(2-3)](-) chelate gradually decomposes in a phosphate environment, but remains stable in an fluoride environment. (C) 2001 Elsevier Science B.V. All rights reserved.