ABSTRACT
The observed water oxidation activity of the compound class Co4O4(OAc)4(Py-X)4 emanates from a Co(II) impurity. This impurity is oxidized to produce the well-known Co-OEC heterogeneous cobaltate catalyst, which is an active water oxidation catalyst. We present results from electron paramagnetic resonance spectroscopy, nuclear magnetic resonance line broadening analysis, and electrochemical titrations to establish the existence of the Co(II) impurity as the major source of water oxidation activity that has been reported for Co4O4 molecular cubanes. Differential electrochemical mass spectrometry is used to characterize the fate of glassy carbon at water oxidizing potentials and demonstrate that such electrode materials should be used with caution for the study of water oxidation catalysis.
Subject(s)
Chemistry Techniques, Analytical , Cobalt/chemistry , Coordination Complexes/chemistry , Water/chemistry , Catalysis , Models, Molecular , Oxidation-Reduction , Quality ControlABSTRACT
A dyad complex has been constructed as a soluble molecular model of a heterogeneous cobalt-based oxygen-evolving catalyst (Co-OEC). To this end, the Co(4)O(4) core of a cobalt-oxo cubane was covalently appended to Re(I) photosensitisers. The resulting adduct was characterised both in the solid state (by X-ray diffraction) and in solution using a variety of techniques. In particular, the covalent attachment of the Re(I) moieties to the Co(4)O(4) core promotes emission quenching of the Re(I) photocentres, with implications for the energy and electron transduction process of Co-OEC-like catalysts.