Electron spin resonance study of the dinuclear copper(II) complexes of 3,6-dioxaoctane-1,8-diamine-NNN′N′-tetra-acetic acid

Abstract

The e.s.r. spectra of aqueous solutions containing copper(II) chloride and 3,6-dioxaoctane-1,8-diamine-NNN′N′-tetra-acetic acid in 2:1 and 1:1 mole ratios and various pH's have been studied. When the metal ion : ligand mole ratio is 2:1 the dinuclear chelate is formed which possesses an e.s.r. signal at room temperature. In frozen solution low-field components of the spectra are observed and have been interpreted in terms of magnetic dipole–dipole coupling between the copper(II) ions. Computer line-shape simulation procedures designed to reveal the symmetry properties of the copper(II) ions in the dinuclear complex by comparison of the experimental line-shape due to the ΔM= 2 transitions with those computed on the basis of axial, orthorhombic, or non-parallel axis symmetry of the copper(II) pair system have been carried out. The results favour a non-parallel axis alignment of the copper(II) ions at a separation of about 4·5 Å in the dinuclear complex. The recently reported triplet e.s.r. spectrum due to a dinuclear molybdenum(V) glutathione complex has been critically assessed to reveal that the symmetry of the molybdenum(V) pair system is lower than axial.