Donor-acceptor complexes axial coordination

The redox potentials of many metalloporphyrin complexes are sensitive to the nature of the electrolyte in which they are measured. This is because one or both axial positions are coordinated by either solvent or anionic ligands. Such dependencies of E° values have been extensively studied by Kadish and coworkers 29 notably good correlation between E° data and Donor/Acceptor Number properties of solvents have been observed. 

An alternative approach for the study of PCET across amidinium-carboxylate interfaces relies on the formation of ternary complexes such as that shown for 16 [141]. A N-propylisonicotinamidine serves as a ditopic spacer between a Zn tetra-phenylporphyrin donor and 3,4-dinitrobenzoate acceptor. The PCET assembly is afforded by the axial coordination of the pyridyl group to the Zn porphyrin (Ka = 1-9 X 10 M 2 in CH2CI2). A benefit of this approach is a significantly reduced synthetic investment required for the incorporation of Dp/Ap into the assembly. Moreover, the system is highly modular and the De porphyrin can be... 

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