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Eighteen Mn complexes with N-donor and carboxylate ligands have been synthesized and characterized. Three Mn complexes among them are new and are reported for the first time. The reactions of oxygen evolution in the presence of oxone (2KHSO5·KHSO4·K2SO4) and cerium(IV) ammonium nitrate catalyzed by these complexes are studied and characterized by UV-visible spectroscopy, X-ray diffraction spectrometry, dynamic light scattering, Fourier transform infrared spectroscopy, electron paramagnetic resonance spectroscopy, transmission electron microscopy, scanning electron microscopy, membrane-inlet mass spectrometry and electrochemistry. Some of these complexes evolve oxygen in the presence of oxone as a primary oxidant. CO2 and MnO4 - are other products of these reactions. Based on spectroscopic studies, the true catalysts for oxygen evolution in these reactions are different. We proposed that for the oxygen evolution reactions in the presence of oxone, the true catalysts are both high valent Mn complexes and Mn oxides, but for the reactions in the presence of cerium(IV) ammonium nitrate, the active catalyst is most probably a Mn oxide. [ABSTRACT FROM AUTHOR]

Here, for the first time, it is reported that some Mn oxides after a few hours convert to a nanolayered Mn oxide when the compounds are used as water-oxidizing catalysts in a water electrolysis device at near neutral pH and in the presence of LiClO4. The new nanolayered Mn oxide is more active than other Mn oxides toward water oxidation. This result is very important for artificial photosynthetic systems that use Mn oxides as water-oxidizing catalysts. [ABSTRACT FROM AUTHOR]

We, for the first time, report that many Mn oxides (Mn3O4, α-Mn2O3, β-MnO2, CaMnO3, Ca2Mn3O8, CaMn3O6 and CaMn4O8) in the presence of cerium(iv) ammonium nitrate, in the water oxidation, convert to layered Mn oxide. This layered Mn oxide is an efficient water oxidizing catalyst. [ABSTRACT FROM AUTHOR]

Nano-sized layered cadmium, magnesium and potassium–Mn oxides were synthesized and characterized by scanning electron microscopy, energy-dispersive X-ray mapping, transmission electron microscopy, X-ray diffraction spectroscopy, and atomic absorption spectroscopy. These oxides showed water oxidizing activity in the presence of cerium(iv) ammonium nitrate as a non-oxo transfer oxidant. The formulae of the best catalysts are Cd0.16MnO2, Mg0.16MnO2 and K0.25MnO2 with an average oxidation state of ∼3.7–3.8 for the Mn ions in the birnessite structure. We also prepared a mixture of redox-active metal ions containing Fe(ii), Cu(ii), Co(ii), and Ni(ii) instead of inert redox ions. Important factors and a proposed self-repair mechanism for the layered Mn oxides in the water oxidation reaction are reported. [ABSTRACT FROM AUTHOR]

Nanolayered Mn oxide/poly(4-vinylpyridine) as a model for Mn cluster in photosystem II was synthesized and characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), dynamic light scattering (DLS), Fourier transform infrared spectroscopy (FTIR) and UV-Visible spectroscopy (UV-Vis). The compound is a very efficient water oxidizing catalyst, and sizable oxygen evolution was detected at 50 mV overpotential at near neutral pH. The number is as low as the overpotential is used by nature in photosystem II of cyanobacteria, algae and green plants for similar reactions. [ABSTRACT FROM AUTHOR]