Cobalt ammines, photoreduction

Photoreduction of Some Bridged Binuclear Cobalt Ammines 179... 

Photolysis of cobalt(III) ammines in the solid state and in various organic media have been reported. Irradiation of crystals of potassium cobaltioxalate gives Co(II) and C02. Study of this reaction by ESR techniques has been reported.69 Photoreduction of Co(NH3)5(H20)l3 gives CoI42- as the cobalt-containing product similar results were obtained with the corresponding bromide and chloride. Solid-state photoreduction of Co(en)3Cl3 has also been reported.70... 

We have initiated a study of the photoreduction of a series of paramagnetic peroxy-bridged dicobalt ammines. All of these complexes, which are shown below, contain the (Co-O-O-Co)5 + group, which best present evidence indicates should be represented as (Co -O-O-Com)5+, although ESR studies indicate that the extra electron is to some extent delocalized over the cobalt centers.78,79,82 Our idea was derived from Sykes report in 196363 that solutions of l-p in sunlight in dilute acid were decomposed according to the stoichiometry shown in reaction (29). 

As always, the photooxidation of water to 2 has received much less attention than the much easier photoreduction of water to H2 However, some notable achievements have appeared and genuine progress has been made. The mechanisms for oxidation of water by metalloporphyrins and cobalt(III) ammines have been studied, with particular attention being given to kinetic parameters. Several new 02 evolving catalysts have been... 

The photochemical decomposition of cobait(m)-ammine-oxalate complexes involves primarily redox processes, as does that of the cis -[Co(bipy)2Cy+ cation.The quantum yield for the photoredox aquation of [Cofphen) is very low - lower even than those for cobalt(m)-amine complexes. The quantum yield for photoreduction of [Co(fra/M-[14]-dieneX l2l is similar to that for photoreduction of [Co(tetren)Cl] + both of these quantum yields are much less than that for the photoreduction of [Co(NH3)5Cl] +. Thermal back-reactions are important in determining the overall kinetic pattern for the photoreaction of the [Co(tra s-[14]-diene)Cl2l+ cation. ... 

---