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

摘要

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 complexes (CuL~(2+)) while the other ligands are likely to form oligomeric complexes (Cu_xL_x~(2x+)), 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.