Relationship between ligand structure and electrochemical and relaxometric properties of acyclic poly(aminocarboxylate) complexes of Eu(II)

A detailed electrochemical study on a series of Eu(III) complexes with multidentate acyclic poly(aminocarboxylate) ligands is reported. For all Eu (III) complexes, a 1e chemically reversible and electrochemically irreversible or quasi-reversible process has been obtained. The electrode kinetics of the 1e reduction of Eu(III) aqua-ion is dependent on the supporting electrolyte as well as on the electrode surface. Pt and glassy carbon electrodes give quasi-reversible responses, whereas mercury shows the better-shaped curves, especially by using sodium ptoluenesulfonate as the supporting electrolyte. Chronoamperometric measurements have been carried out in the temperature range 1-35 °C and the diffusion coefficients of a few Eu(III)/Eu(II) complexes evaluated. The 1/T11H nuclear magnetic relaxation dispersion (NMRD) curves have been measured at 25 °C in aqueous solution for selected Eu(II) complexes, analysed in terms of the standard theory of paramagnetic relaxation and compared with existing data for the isoelectronic Gd(III) derivatives.