The Electrochemical Study of Ag(II) Complexes of Polyaza Macrocycles and Their Acetic Acid Derivatives

Abstract

Abstract Although an attempt to isolate pure crystallines of Ag(II) complexes failed, we could prepare stable aqueous solutions of the Ag(II) complexes of [15]aneN5, [16]aneN5, and their acetic acid derivatives by disproportionation reactions of Ag(I) induced by these polyaza macrocycles, and have investigated their electrochemical redox behaviors using conventional voltammetric methods. All Ag(II) complexes including the [14]aneN4 (cyclam) complex undergo a reversible two-electron reduction at DME (dropping mercury electrode). From the potential where the i2⁄(i1–i) ratio is unity, the log formation constants were determined to be 43.4, 43.6, 43.3, 39.3, and 42.5 for the cyclam, [15]aneN5, [16]aneN5, cyclam-tetraacetic acid, and [15]ane5-pentaacetic acid complexes, respectively. Cyclic voltammetric (CV) oxidation scans at the glassy carbon electrode showed a reversible one-electron response (separation of anodic and cathodic peak potentials, ΔEp′=70 mV; the ratio of anodic and cathodic peaks, (ip)c⁄(ip)a′=1), which can be ascribed to a reversible Ag(III)/Ag(II) redox change. Though the acetate groups attached to the nitrogen atoms contribute to the net destabilization of the Ag(II) complexes, they exert a large positive effect on the thermodynamic stability of the Ag(III) state.