Photoredox decomposition

Finally, the photoredox decomposition of K3[Mn(C204)3]-3H20 has been proposed for use as an actinometer for solid state photochemical studies.180 Upon UV irradiation, the crystals of this complex change from deep red to white and the extent of reaction can be measured easily by reflectance spectroscopy. 

Photolysis of oxalate complexes show that there is a strong tendency to undergo photoredox decompositions, resulting in oxides of carbon. Two useful applications of this are (i) the system based on the redox photolysis of aqueous [Fe(C204)3]3- is widely used for chemical actinometry 100 and (ii) UV irradiation of (phos)2M(C204) complexes (M = Pd, Pt) result in loss of two molecules of carbon dioxide and production of the synthetically useful, coordinatively unsaturated M° complex (phos)2M.19 One reaction which, if generally applicable to dicarboxylate complexes, may have considerable impact upon the validity of physical measurements upon these systems is the rather unusual, room temperature, solid-state reaction (2).102... 

Production of a molecule of oxygen (02) from water via photoredox decomposition is, mechanistically, a more difficult process involving a concerted 4-electron transfer ... 

For the product formation a variety of possibilities exists. If the complex fragment or the ligand radical undergo a rapid irreversible reaction stable photoredox products are obtained. For example, the complex fragment Co(NH3>52+ in water decays to Co(H20)g2+ and ammonia with k > 10 s l [95]. Accordingly, the photoredox decomposition of Co(ni) pentaammine complexes proceeds by equation (4) (X = halogen)... 

In the case of Colil(CN)5X3- such a photoredox decomposition is not expected to take place since the primary complex fragment Co KCN)53- does not decay but undergoes a recombination with X- (or X2) [94]. However, if the ligand radical reacts rapidly and irreversibly Co(CN)5X3- will also yield stable photoredox products, e.g. (X = benzyl) [96] ... 

Photopolymerizable coatings relief-image-forming systems, 6,125 Photoreactivity environmental effects, 1, 394 Photoredox properties bipyridyl metal complexes, 2, 90 Photoresist systems, 6,125 Photosensitive materials, 6, 113 Photosynthesis anoxygenic, 6, 589 magnesium and manganese, 6, 588 water decomposition models, 6, 498... 

Most of the available information about the reactivity of CTTM excited states comes from studies of Cora acidoammines.91 92 Typically, irradiation of a CTTM absorption band in these systems leads to efficient redox decomposition accompanied, in many cases, by ligand substitution or linkage isomerization. The behavior of a representative complex, [CoC1(NH3)5]2+, is summarized in equation (39).93 A common observation in these systems is that photoredox quantum yields increase at shorter excitation wavelengths and decrease with increasing solvent viscosity.91 92... 

Ru(bpy)32+-sensitized redox decomposition of Co(III) complexes is one of the first photochemical reactions reported and the establishment of the mechanisms has been controversial[33,34]. Since this is a typical case in studies of photoredox and energy transfer reactions, we elaborate on the controversy in order to appreciate the difficulties. Co(III) complexes such as [Co(NH3)5X]2+ upon photoreduction to the Co(II) state readily decompose, yielding the aquo Co(II) ions (X =CF, Br or F) ... 

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. ... 

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