Potentiometric and spectroscopic studies of copper(II) complexes of bis(1,4,7-triazacyclononane) ligands containing polymethylene and xylyl linker groups

Copper(II) complexes of bis(1,4,7-triazacycloaonane) ligands with seven- and eight-membered polymethylene chains and xylyl bridging groups were studied in aqueous solution by pH potentiometry and UV-Vis spectroscopy. Equilibrium modeling of the data indicates that with all the ligands studied both 1:1 and 2:1 Cu(II)L complexes are stable. The Cu2L4+ complexes all have similar stability and appear to contain the same coordinative environment. The o-xylyl bridged complex forms a very stable monomeric complex (CuL2+) while the other ligands are likely to form oligomeric complexes (CuxLx2x+), which are less stable. The impact of ligand structure on the stoichiometry and stability of the complexes is discussed. The X-ray structure of the binuclear complex [Cu-2(EM8)Cl-4] was determined. The distorted square pyramidal coordination polyhedron is similar to that found with other copper(II) complexes of 1,4,7-triazacyclononane. (C) 1999 Elsevier Science S.A. All rights reserved.