Electrochemically Driven Generation of Manganese(IV,V)-oxo Multiporphyrin Arrays and Their Redox Properties with Manganese(III) Species in Langmuir-Blodgett Films

High-valency manganese (IV,V)-oxo porphyrins have been electrochemically generated and in situ spectrally characterized in multiporphyrin arrays, which were formed by an interfacial coordination reaction of Na₂PdCl₄ with manganese (III) tetrapyridylporphyrin (MnTPyP). Multilayers of the Pd-MnTPyP multiporphyrin arrays were obtained by the Langmuir−Blodgett (LB) method. The redox behaviors of manganese in the multiporphyrin arrays were pH-dependent. Spectroelectrochemical experiments revealed a reversible redox process between Pd−Mn^(III)TPyP and its Mn(IV)-oxo species, but an irreversible process between Pd−Mn^(III)TPyP and its Mn(V)-oxo species. The Pd−Mn^(IV)TPyP multiporphyrin arrays could be spontaneously reduced to their Mn(III) complex, while the Pd−Mn^(V)TPyP arrays were rather stable in basic solutions (pH > 10.5). However, when the Pd−Mn^(V)TPyP multiporphyrin arrays were washed by or immersed in water, they were immediately reduced to their Mn(III) complex. Because these well-organized multiporphyrin arrays are of high thermal and chemical stability, they are potential molecular materials in the studies of natural and artificial catalytic processes as well as redox-based molecular switches.