K4Mo4O12(O2)2 and K4W4O12(O2)2.4H2O were prepared from K2MoO4 or K2WO4, resp., and H2O2 at pH 7.3. The products were characterized by IR, Raman and cyclic voltammetry studies. Both compounds were reduced at a Pt electrode vs. SCE at E1 = 0.317, 0.172 V, resp. and E2 = 0.226, <-0.2 V, resp. They were oxidized at E3 = 0.862, 0.786 V, resp. The Mo compound decomposed after a 1-electron reduction Both compounds decomposed after the 4-electron oxidation at E3.

Key words: OXIDATION REDUCTION REACTION, INFRARED SPECTROPHOTOMETRY, MOLYBDENUM COMPLEX, PEROXIDE, POTENTIOSTAT, CYCLOVOLTAMGRAPH, TUNGSTEN COMPLEX, DECOMPOSITION ELECTRIC POTENTIAL, RAMAN SPECTROMETRY