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 d(4)S = 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 pK(a) values is obtained by fitting the data to a standard pK(a) 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 pK(a) values and electrochemistry data are discussed in the context of the development of mononuclear water-oxidation catalysts.
[Show abstract][Hide abstract] ABSTRACT: Three new substituted manganese phthalocyanines (PcMns), wich are water-soluble, have been synthesized with good yields (70–80%) and high purity. Pyridiniummethyl- and cholinylsubstituted phthalocyanines have been obtained from the chloromethylsubstituted PcMns, while octacarboxysubstituted complex has been synthesized from metal-free octacarboxyphthalocyanine tetraanhydride. Compounds were characterized by elemental analysis and mass, IR and UV-vis spectroscopy. In general, coordination chemistry of the compounds studied is similar to this one of liposoluble PcMns but some new findings have been obtained. Three coordination forms — PcMn(II), PcMn(III)X(X = Cl-, OAc-, …) and [LPcMn(III)]2O(L = Py, Et3N, …) have been obtained for all the new compounds. The equilibrium between three electronic isomers — Pc+•Mn(I) × L, PcMn(II) × nL, (n = 1, 2) and Pc-•Mn(III) × 2L has been observed in PcMn aqueous solutions upon the addition of organic bases L (Py, Et3N, …).
Journal of Porphyrins and Phthalocyanines 08/2013; 17(08n09). DOI:10.1142/S1088424613500818 · 1.40 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Novel tetra aminopropylamid substituted phthalocyanines were synthesized as zinc(II), cobalt(II), copper(II) and manganese(II) metallophthalocyanines. The synthesis of the phthalocyanines 3-6 was achieved by the tetramerization of 4-subtituted phthalonitrile, 2-(3,4-dicyanophenoxy)ethyl-N-(3-dimethylaminopropyl)carbamate (2), prepared via the nucleofilic aromatic substitution of 4-nitro phthalonitrile and 2-hydroxyethyl-N-(3dimethylaminopropyl) carbamate (1). Solution properties of the prepared phthalocyanines were investigated by the examination of their UV-vis spectra. The zinc Pc showed surprisingly high solubility in water. The aggregation properties of the Pcs were examined in different organic solvents and water. The substituents on the periphery position of the phthalocyanine molecules acted as non-ionic surfactant and increased the solubility in hydrophilic solvents and water. Quaternization of these groups improved the solubility, as well.
[Show abstract][Hide abstract] ABSTRACT: The new tetra peripheral 3,5-bis(trifluoromethyl)phenylethynyl substituted metallophthalocyanines (MPc) have been synthesized and their aggregative properties were investigated in different concentrations. Voltammetric and in situ spectroelectrochemical characterization of MPcs bearing metal centers with higher oxidation states In-III, Mn-III, and Ti-IV were performed in solution. While (InClPc)-Cl-III gave only Pc ring based reduction process, (MnClPc)-Cl-III and (TiOPc)-O-IV showed metal based reduction reactions in addition to Pc-based redox processes. The presence of redox active metal centers like (MnCl)-Cl-III and (TiO)-O-IV in the core of Pc ring increases the electrochemical activity of the complexes. The redox responses of the complexes confirmed the submitted structure of the complexes. During the electrochemical measurements, it was noticed that the presence of molecular oxygen in the electrolyte system considerably influenced the redox responses of the complexes due to the interaction of MPcs with O-2, which indicated the electrocatalytic and/or electrochemical sensing activities of the complexes for O-2 sensing. Electrocatalytic oxygen reduction and oxygen sensing measurements were performed in solution and in solid states as Langmuir-Blodgett multilayer thin films. While (InClPc)-Cl-III did not give any voltammetric signal for the interaction with molecular oxygen, square wave voltammetric (SWV) responses of (MnClPc)-Cl-III and (TiOPc)-O-IV show electrocatalytic activities of the complexes for oxygen reduction reactions (ORR). Moreover, interaction of O-2 with these complexes gave extraordinary anodic SWV signals in both of aprotic and protic solvents, which indicate possible usage of the complexes as molecular oxygen sensor.
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