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Issue 25, 2012
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Aqueous speciation and electrochemical properties of a water-soluble manganese phthalocyanine complex

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Abstract

The speciation behavior of a water-soluble manganese(III) tetrasulfonated phthalocyanine complex was investigated with UV-visible and electron paramagnetic resonance (EPR) spectroscopies, as well as cyclic voltammetry. Parallel-mode EPR (in dimethylformamide : pyridine solvent mix) reveals a six-line hyperfine signal, centered at a g-value of 8.8, for the manganese(III) monomer, characteristic of the d4S = 2 system. The color of an aqueous solution containing the complex is dependent upon the pH of the solution; the phthalocyanine complex can exist as a water-bound monomer, a hydroxide-bound monomer, or an oxo-bridged dimer. Addition of coordinating bases such as borate or pyridine changes the speciation behavior by coordinating the manganese center. From the UV-visible spectra, complete speciation diagrams are plotted by global analysis of the pH-dependent UV-visible spectra, and a complete set of pKa values is obtained by fitting the data to a standard pKa model. Electrochemical studies reveal a pH-independent quasi-reversible oxidation event for the monomeric species, which likely involves oxidation of the organic ligand to the radical cation species. Adsorption of the phthalocyanine complex on the carbon working electrode was sometimes observed. The pKa values and electrochemistry data are discussed in the context of the development of mononuclear water-oxidation catalysts.

Graphical abstract: Aqueous speciation and electrochemical properties of a water-soluble manganese phthalocyanine complex

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Publication details

The article was received on 16 Feb 2012, accepted on 12 Apr 2012 and first published on 17 Apr 2012


Article type: Paper
DOI: 10.1039/C2DT30371J
Citation: Dalton Trans., 2012,41, 7681-7688
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    Aqueous speciation and electrochemical properties of a water-soluble manganese phthalocyanine complex

    J. D. Blakemore, J. F. Hull, R. H. Crabtree and G. W. Brudvig, Dalton Trans., 2012, 41, 7681
    DOI: 10.1039/C2DT30371J

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