Ca. Bessel et Dr. Rolison, TOPOLOGICAL REDOX ISOMERS - SURFACE-CHEMISTRY OF ZEOLITE-ENCAPSULATEDCO(SALEN) AND [FE(BPY)(3)](2+) COMPLEXES, JOURNAL OF PHYSICAL CHEMISTRY B, 101(7), 1997, pp. 1148-1157
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.