Peroxo linkage

Much work has been devoted to the study of Schiff base complexes, in particular M(salen), where M = metal, has been the subject of extensive work 114). The early work by Calvin et al. (section 111(A)) suggested that the 2 1 (M O2) dioxygen adduct, type I, formed by Co(salen) in the solid state, contains a peroxo linkage. An X-ray analysis 115, 116) of the complex (Co Salen)202(DMF)2 supports this hypothesis see Fig. 5 for the pertinent results of this study. 

Fig. 11. Dinuclear cobalt(III) complexes bridged by a peroxo linkage and either thiosulfate -) (56) or benzenethiolatef 1") (57).

Heteropolyoxoperoxotungstate complexes containing the peroxo linkage are dso effective oxidation catalysts with hydrogen peroxide. 

In this new type of coordination mode d(O-O) is long (147 pm) and the weakness of the 0-0 linkage is also shown by the very low value of 851 cm for v(O-O), both values being more characteristic of peroxo than of superoxo complexes/ ... 

In 2000 Meyer and co-workers reported a novel example of unusual 4-peroxo coordination (complex (146)), as well as of a structurally analogous complex in which the 0-0 linkage is formally cleaved and replaced by two OH units (147), while at the same time the overall tetra-nuclear framework is fully conserved.145... 

The two oxides formed with hydrogen, H20 and H202, have already been discussed, but it should be emphasised that hydrogen peroxide and the peroxides formed from it contain the —O—O— linkage. The oxidising power of these peroxides lies in the oxygen of the peroxo-group. unlike the dioxides (see above). 

Co-ordination Position Isomerism.—Here the isomerism occurs through the arrangement of the groups around each cobalt atom with respect to the bridged linkage. For example, there are two dibromo-hexammino-amino-peroxo-dicobaltic bromides which are represented thus ... 

The acetamide linkages in 1 and 2 provide enough flexibility to the distal imidazole ligands, and they are short enough to keep Cu-Fe distance within the 4,5-5,5 A range, but not to coordinate to the iron atom [242], Oxygen binds irreversibly with 1 or 2 to form a putative peroxo-Fe (0 )Cu intermediate, which is too unstable to be characterized [243],... 

Organic peroxides (R202) and peroxoacids (e.g. the percarbonate ion, 2) contain the fairly weak peroxo O—O linkage. Some covalent peroxides can be unpredictably and dangerously explosive. 

However, the similarity in bond strengths of the peroxide linkage to molecular 02, the ease with which the known -peroxo Cobalt complexes liberate 02 (in contrast to /x-oxo bipyridyl Mn dimers) on photolysis, kinetic barriers on ju-oxo to peroxo dimer conversions led Sawyer et al.47 -49) to suggest peroxo binuclear complexes as the most probable intermediates. More studies with model compounds are needed to elucidate this point. Various mechanisms proposed for water oxidations are variations of these two principal types. 

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