Cu(II) and Ni(II)-1,10-phenanthroline- 5,6-dione-amino acid ternary complexes exhibiting pH-sensitive redox properties

Abstract

Syntheses, and electrochemical properties of two novel complexes, [Cu(phendio)(L-Phe)(H2O)](ClO4) ·H2O (1) and [Ni(phendio)(Gly)(H2O)](ClO4)·H2O (2) (where phendio = 1,10-phenanthroline-5,6-dione, L-Phe = L-phenylalanine, Gly = glycine), are reported. Single-crystal X-ray diffraction results of (1) suggest that this complex structure belongs to the orthorhombic crystal system. The electrochemical properties of free phendio and these complexes in phosphate buffer solutions in a pH range between 2 and 9 have been investigated using cyclic voltammetry. The redox potential of these compounds is strongly dependent on the proton concentration in the range of − 0.3–0.4 V vs SCE (saturated calomel reference electrode). Phendiol reacts by the reduction of the quinone species to the semiquinone anion followed by reduction to the fully reduced dianion. At pH lower than 4 and higher than 4, reduction of phendio proceeds via 2e−/3H+ and 2e−/2H+ processes. For complexes (1) and (2), being modulated by the coordinated amino acid, the reduction of the phendio ligand proceeds via 2e−/2H+ and 2e−/H+ processes, respectively. Copyright © 2006 John Wiley & Sons, Ltd.