Topological redox isomers

Located outside the zeolite, with no bonding or sorptive association 

Adsorbed into the voids of the zeolite but able to sample the global pore lattice topology 

Size-included in the interior of supercages or channel intersections of the zeolite framework 

Electrochemical methods provide information on the coexistence of different topological redox isomers. Discrimination between different redox isomers can 

In contact with size-excluded HCX4N and BU4N+ cations, an apparently unique, broad reduction peak is obtained. In the presence of I LI4N, the voltammetric signal becomes significantly enhanced and reduced to a tall peak. Chronoamperograms 

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C.A. Bessel and D.R. Rolison, Topological Redox Isomers Surface Chemistry of Zeolite-encapsulated Co(salen) and [Fe(bpy)3]2+ Complexes. J. Phys. Chem. B, 1997, 101, 1148-1157. 

Concentration profiles for the variation of the concentration of the different topological redox isomers with depth were estimated from chronoamperometric and chronocoulometric data. Application of methods described in Section 2.5 led researchers to establish that the electrochemical process represented by Equation (4.9) is controlled by electron diffusion with = 1 x 10 crnVscc (Domenech et al., 2009). Resulting curves are shown in Figure 4.20 for a three-isomer system. 

Peak splitting (see Figure 8.22) can be attributed to the superposition of processes due to iron species in different zeolite sites (topological redox isomers, see Chapter 4) and also to the occurrence of chloride-assisted reduction processes. 

The response of BTP Y in Bi N /MeCN is restricted to a unique reduction process near to -0.40 V, but it differs signihcantly in the presence of Et4N+. Here, two reduction processes at -0.22 and -0.36 V appear (Figure 11.2). As described in Chapter 4, this response can be associated to the presence of different boundary-associated topological redox isomers for which no signihcant comproportionation reaction occurs, namely. 

Bessel, C.A., and Rolison, D.R. 1997a. Topological redox isomers Surface chemistry of zeolite-encapsulated Cofsalcn) and fc(bpv),P complexes. Journal of Physical Chemistry B 101, 1148-1157. 

Domenech, A., Formentin, P, Garcia, 11,. and Sabater, M.J. 2002a. On the existence of different zeolite-associated topological redox isomers. Electrochemistry of Y zeolite-associated Mnfsalen )Ni complex. Journal of Physical Chemistry B 106, 574-582. 

Figure 2.1 A square scheme illustrating a redox-driven intramolecular motion. Species with an asterisk (Ox and Red ) are metastable and tend to rearrange to their stable topological isomer (Ox and Red).

Receptor 17 has a similar topology—it comprises four cobaltocenium amide groups attached to a porphyrin backbone as the cis-a,a,a,a-eLtrop-isomer [19]. Proton NMR titrations in CD3CN showed chloride and bromide to be bound in 1 1 stoichiometry with stability constants of 860 and 820 M respectively, whereas nitrate exhibited weaker binding with JC = 190 M Electrochemical studies displayed cathodic shifts in the cobal-tocene/cobaltocenium redox couple of 35-75 mV on addition of chloride or hydrogensulfate, and 225 mV for dihydrogenphosphate in acetonitrile solu-... 

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