Cr-containing derivatives of PW, ,O& heteropolyanion (PW, ,Cr) were synthesized under variation of precursors and procedure (increasing temperature, prolonged keeping of solution, varying molar ratio of starting reagents and acidity) and characterized by elemental analysis, UV-Vis and IR spectroscopy. Tetrabutylammonium salts of PW, ,Cr were examined in catalysis of H,O, decomposition and oxygen transfer from H,O, to the hydrocarbon substrates, cyclohexene and benzene. With all the other conditions of synthesis identical, increasing the pH gave samples more active in H,O, decomposition. In the H ,O,/PW, ,Cr system, benzene formed phenol and cyclohexene formed a mixture of cyclohexenone, cyclohexenol and cyclohexene oxide. The activity of PW,,Cr in hydrocarbon oxidation was sensitive to the procedure used for sample synthesis. Variable spectral characteristics and catalytic properties of PW,,Cr samples were suggested to depend on the nature of bond between Cr(III) ion and PW, ,O:, anion. As distinguished from typical M-substituted polyoxometalates, the samples obtained contain Cr(III) ions which are probably connected with surface oxygen atoms of PW, ,O:; heteropolyanion near the vacancy of the Keggin structure. Surface location of C&II) ions is supposed to favor oxygen transfer from H,O, to hydrocarbon. In the presence of H,O,, PW,,Cr solutions showed the increase of visible absorption and a shift of its maximum from 15200-16300 to 15500-18000 cm-', that arose from the reaction of PW, ,Cr with intermediate products of the H,O, decomposition.
The resulting oxidized species PW,,CdO] are active oxidants in the reaction with unsaturated hydrocarbons.