Abstract
Macrocyclic tetraamine "cyclen" derivatives having four cation-ligating sidearms effectively bind sodium, some transition metals, and lanthanide ions to form stable octadentate complexes having helical structures.We have developed various armed cyclen-sodium complexes in which all the ligating sidearms have the same functional group. The log K values for their sodium complexes were estimated as 9-11 in CD3CN or C2D5OD, which were comparable to those of common bicyclic cryptands.In this study, we introduced one different sidearm to the tetra-armed cyclen sodium complexes, and characterized the structures and stability constants of complexes with X-ray diffraction and NMR methods. NMR titration revealed that such mixed armed cyclens exhibited larger binding constants than the parent armed cyclens. In 1H-NMR spectrum of octadentate sodium complex with mixed armed cyclen (1 x Bn2NCOCH2- and 3 x EtOCOCH2-), proton signals of three ethyl ester-sidearms were observed separately, and proton signals for the ethyl ester next to the amide sidearm broadened. These suggest that this octadentate complex has twisted helical structure in CD3CN solution, and effective coordination from the amide sidearm affects the geometry of the other sidearms.The synthesis, structure and stability for various sodium complexes with mixed armed cyclens will be also reported.
