Concerted and stepwise proton-coupled electron transfers in aquo/hydroxo complex couples in water: oxidative electrochemistry of [Os(II)(bpy)(2)(py)(OH(2))](2+)

Successive oxidation of transition metal(II) aqua complexes (M(II)OH(2) to M(III)OH) is a domain in which proton-coupled electron transfer reactions are extremely common. The mechanism of these PCET reactions-concerted or stepwise-is an important issue in the understanding and design of natural or artificial systems catalyzing the formation of dioxygen by four-electron oxidation of water. Concerted proton-coupled electron transfer from an aqua metal(II) to a hydroxo metal(III) complex requires the close proximity of a proton-accepting group with a pK value between those of the aqua complexes. Otherwise, stepwise electron-proton or proton-electron pathways involving high-energy intermediates are followed. Concerted proton-electron pathways involving water as proton-acceptor or proton-donor group are inefficient. Cyclic voltammetry of the title complex in buffered aqueous solution and re-examination of previous results for the same complex attached to an electrode surface are used to establish these conclusions, which provide a starting point on the route to higher degrees of oxidation, such as those involved in the catalysis of water oxidation.     

Encapsulation of filaments of a self-assembling bicopper complex in polymer nanowires

We report on the preparation conditions and the characterization by calorimetry and small-angle neutron scattering of a molecular composite material obtained via the heterogeneous nucleation of the fibrils of a thermoreversible gel. This physical process allows encapsulation of monomolecular filaments of a self-assembling bicopper complex into nanosized polymer fibrils. Due to the existence of 1-D arrangements of copper atoms, this material may possess unusual magnetic properties (spin ladders). Received 20 January 1999 and Received in final form 14 May 1999