What determines catalyst functionality in molecular water oxidation? Dependence on ligands and metal nuclearity in cobalt clusters.

The metal-oxo M4O4 "cubane" topology is of special significance to the field of water oxidation as it represents the merging of bioinspired structural principles derived from natural photosynthesis with successful artificial catalysts known to date. Herein, we directly compare the rates of water oxidation/O2 evolution catalyzed by six cobalt-oxo clusters including the Co4O4 cubanes, Co4O4(OAc)4(py)4 and [Co4O4(OAc)2(bpy)4](2+), using the common Ru(bpy)3(2+)/S2O8(2-) photo-oxidant assay. At pH 8, the first-order rate constants for these cubanes differ by 2-fold, 0.

A Co4O4 "cubane" water oxidation catalyst inspired by photosynthesis.

Herein we describe the molecular Co(4)O(4) cubane complex Co(4)O(4)(OAc)(4)(py)(4) (1), which catalyzes efficient water oxidizing activity when powered by a standard photochemical oxidation source or electrochemical oxidation. The pH dependence of catalysis, the turnover frequency, and in situ monitoring of catalytic species have revealed the intrinsic capabilities of this core type. The catalytic activity of complex 1 and analogous Mn(4)O(4) cubane complexes is attributed to the cubical core topology, which is analogous to that of nature's water oxidation catalyst, a cubical CaMn(4)O(5) cluster.

Development of bioinspired Mn4O4-cubane water oxidation catalysts: lessons from photosynthesis.

Hydrogen is the most promising fuel of the future owing to its carbon-free, high-energy content and potential to be efficiently converted into either electrical or thermal energy. The greatest technical barrier to accessing this renewable resource remains the inability to create inexpensive catalysts for the solar-driven oxidation of water. To date, the most efficient system that uses solar energy to oxidize water is the photosystem II water-oxidizing complex (PSII-WOC), which is found within naturally occurring photosynthetic organisms.