Lanthanide complexes of 1,4,7,10-tetra-azacyclotridecane-1,4,7,10-tetra-acetic acid: proton nuclear magnetic resonance studies

Abstract

The conformation in solution of some lanthanide(III) complexes of 1,4,7,10-tetra-azacyclotridecane-1,4,7,10-tetra-acetic acid has been studied by ¹H n.m.r. techniques. The results suggest that these complexes have an approximate square-antiprism geometry in solution, with the lanthanide ion lying in a shell above the plane defined by the four nitrogens of the ligand and below that of the co-ordinated carboxylate oxygens. The tetra-aza ring in these complexes prefers a [12433] conformation, being less flexible than in the complexes of the corresponding 14-membered ring and being comparable with that of the more common 12-membered ring.