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

Abstract

Copper(II) complexes of bis(1,4,7-triazacyclononane) 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 Cu 2L 4+ complexes all have similar stability and appear to contain the same coordinative environment. The o-xylyl bridged complex forms a very stable monomeric complex (CuL 2+) while the other ligands are likely to form oligomeric complexes (Cu x L x 2 x+ ), 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.