Redox properties of (1-(2-pyridylazo)-2-naphthol)copper(II) encapsulated in Y Zeolite

Abstract

The electroactivity of zeolite-encapsulated redox-active transition metal complexes was explored for copper(II)-PAN (PAN = 1-(2-pyridylazo)-2-naphthol) complex encaged in the supercages of Y zeolite. Copper(II)-PAN complex and the zeolite boundary were investigated electrochemically by dispersion with a Nafion/water solution on carbon Toray as supporting electrode. Encapsulation was achieved by: (i) ion exchange of copper(II) in NaY zeolite and (ii) coordination of the intrazeolite metal ion with the PAN ligand using an L:copper(II) molar ratio of 2:1. The resulting materials were characterized by cyclic voltammetry in zeolite modified electrodes, surface analysis (XPS, SEM and XRD), spectroscopic methods (EPR and FTIR) and chemical analysis, which indicated that the copper(II)-PAN complex was effectively encapsulated inside the supercages of NaY, without any modification of the morphology and structure of the zeolite. The coordination geometry of Y-encapsulated copper(II)-PAN complex has been obtained with preferentially 1:1 stoichiometry analogous to the model complex, [CuCl(PAN)], by molecular simulations. For the cyclic voltammetry studies, the electrochemical behavior of free complex was compared with copper(II)-PAN complex encapsulated in Y zeolite. The results show evidence for electroactivity restricted to the boundary associated to the copper(II)-PAN complex.