31P NMR Studies of Hydrolytic Conversions of 12-Tungstophosphoric Heteropolyacid
Coordination Chemistry Reviews
, E-ISSN: 1873-3840
||Tungsten Phosphorus Polyoxometalates Base hydrolysis NMR spectroscopy
Maksimovskaya Raisa I.
Maksimov Gennady M.
Boreskov Institute of Catalysis, Siberian Branch of RAS, Lavrentiev pr. 5, Novosibirsk 630090, Russia
Federal Agency for Scientific Organizations
Tungsten and molybdenum heteropolyacids produced in acidified aqueous solutions are an important class of polyoxometalates. The 12-tungstophosphoric heteropolyacid, H3PW12O40, and numerous tungstophosphates, obtained upon alkalization, are widely applied in different areas of chemistry, material science and medicine. Consequently, understanding of hydrolytic conversions of H3PW12O40 is of great fundamental and practical significance. On the basis of numerous studies carried out for more than
a century, the concept of the base degradation of H3PW12O40 was largely formulated in the 1980s. The application of the multinuclear NMR spectroscopy has resulted in significant progress in characterizing polyoxotungstates in solution. At the same time, 31P NMR studies of hydrolytic conversions of H3PW12O40 have led different research groups to contradicting conclusions on the correctness of its previously accepted degradation scheme. In the present review, we discuss to which extent these conclusions are actually confirmed by NMR and consider in more detail the mechanism of the base decomposition of H3PW12O40 on the basis of all available data. The possibilities and limitations of NMR spectroscopy on different nuclei in studying tungstophosphates are also discussed.