SPECTROSCOPIC AND STRUCTURAL-PROPERTIES OF SOME MOLYBDENUM AND TUNGSTEN POLYOXOPEROXO COMPLEXES - A COMPARISON WITH MONONUCLEAR COMPLEXES

Polyoxoperoxo complexes (PPC), either generated in situ by addition of H2O2 to heteropoly acids or isolated, appear to be more versatile oxidants of organic substrates than mononuclear peroxo complexes of the same metals, namely Mo and W, both anionic or neutral. The comparison of some spectroscopic properties of a series of PPC with those of simple peroxo complexes indicates that no major differences between the two families of oxidants are observed. Thus, the remarkable electrophilic reactivity of PPC, which are effective epoxidizing agents, in contrast to anionic simple peroxo complexes, may be explained by a more effective charge delocalisation in the former peroxo complexes. Moreover, O-17-NMR data concerning the line widths of the peroxo oxygens of PPC, seem to indicate a high degree of ion pairing of these species which should serve to reduce their anionic character. The structure of a Mo(VI)-PPC has been determined by diffractometric analysis and compared with that of a W(VI) derivative already reported in the literature. Also such a comparison does not reveal appreciable differences in the solid state structures of PPC.