TOPOLOGICAL REDOX ISOMERS - SURFACE-CHEMISTRY OF ZEOLITE-ENCAPSULATEDCO(SALEN) AND [FE(BPY)(3)](2+) COMPLEXES

The electroactivity of zeolite-encapsulated redox-active transition me tal complexes, {M(L)}Z, was explored for Co(salen) and [Fe(bpy)(3)](2) formed in NaY zeolite (where salen = N,N'-bis(salicylidene)ethylened iamine and bpy = 2,2'-bipyridine). The zeolite boundary was characteri zed via X-ray photoelectron spectroscopy (XPS) and cyclic voltammetry in nonaqueous electrolyte at either zeolite-modified electrodes (ZMEs) or a stirred microheterogeneous dispersion of the redox-modified zeol ite. Voltammetric incongruities arising for {M(L)}Z studied as a ZME r ather than as a dispersion are attributed to changes imposed on the re dox-modified zeolite by the mechanical force used to prepare a ZME. an increase in the time in which a mixture of {[Fe(bpy)(3)](2+)}NaY and carbon are either ground or pressed produces improved peak resolution and an initial but short-lived increase in the magnitude of the voltam metric peak currents. Cyclic voltammetry of a stirred dispersion of {M (L)}Z particles at a large surface area electrode yields fewer complic ations attributable to the electrode binders, carbons, or mechanical h andling necessary to prepare a zeolite-modified electrode. Unlike its response in a ZME, {Co(salen)}NaY gives stable voltammetry for hours w hen characterized in a microheterogeneous dispersion. Using terminolog y analogous to that established in the study of zeolite-associated pho tochemical probes, we reconcile the range of voltammetric responses ob served for a given redox-modified zeolite, both in our results and tho se in the literature, as due to the type of topological redox isomer e xpressing the electroactivity. The voltammetry obtained with both ZMEs and heterogeneous dispersions of zeolite-encapsulated transition meta l complexes provides evidence for electroactivity restricted to bounda ry-associated complexes.