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Cyclic voltammetric data are presented for electrodes coated with zeolite Y powder containing porphyrins and viologens. Half-wave potentials for viologen cations (methylviologen, benzylviologen, or N,N'-( 1,3-propenyl)-2,2'-bipyridinium) do not change significantly when they are exchanged into zeolite Y, whereas the reduction potentials for cobalt and zinc tetrakis(7V-methyl-4-pyridyl)porphyrins shift (relative to aqueous solution) by +200 mV. When a viologen cation is ion exchanged into the bulk of the zeolite, and cobalt tetrakis(7V-methyl-4-pyridyl)porphyrin is adsorbed onto its outer surface in monolayer quantities, current rectification and charge trapping reactions are observed. The charge "untrapping" reactions are similar to those previously observed at redox polymer bilayer electrodes and are attributed to a kinetically fast cross reaction between doubly reduced viologens inside the zeolite and cobalt(II) porphyrin on the outer surface. Rotating disk experiments show that the porphyrin monolayer effectively seals up the zeolite against exchange of encapsulated viologens with solution-phase cations.

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the Cu(II) center, particularly changes in coordination number accompanying loss of ligated water. The bis(diimine) values are closer to the highest apparent self-exchange rate constant {k22 = 1.3 X 105 M"1 s"1) estimated22 for the blue copper protein plastocyanin, in which a coordination number change is precluded by the rigid Cu center, held inaccessible to solvent by the enveloping protein. Cu(II)-H20 bond breaking does not appear to make a significant contribution to the activation process of the Cu(tmbp)22+ and Cu(dmbp)22+ reactions. The similarity in the k22 values estimated from Cu(tmbp)2+-Ru(III) and Cu-(tmbp)22+-Ru(II) cross-reaction data also accords with this. The second-order rate constant (k2 = 4 X 105 M"1 s"1) measured for the oxidation of Cu(tmbp)2+ by ds-[Ru(NH3)4(isn)2]3+ yields a value of 1 X 104 M"1 s"1 for Cu(tmbp)2+/2+ self-exchange. For the corresponding bipyridyl and phenanthroline couples Cu-

Can. J. Chem. 69, 3 15 (1991). The synthesis of 2,2':4,4":6,2"'-quaterpyridine and 2,2':4,4"-terpyridine was accomplished by a reverse aldol condensation reaction of the appropriate aldehyde with alkyl and pyridyl acetyls. A selective quaternization method in toluene is described. In this method the 1,l' nitrogens survive alkylation and are free to coordinate with metals to form metal complexes. The electrochemical behaviour of the neutral ligands as well as the monoquaternized cations was established by linear sweep cyclic voltammetry. Spectroelectrochemical techniques were used to establish the electronic spectral behaviour and stability of the radicals obtained upon reduction.