Synthesis, characterization and electrocatalytic behaviors of α-K6[As2W12Mo6O62] · 12H2O

Pure α-K6[As2W12Mo6O62] · 12H2O was synthesized for the first time. It was obtained in high yield by careful consideration of the main experimental parameters. Keys to the successful achievement of this synthesis include the high acidity of the medium, the order of addition of reactants, the necessity of keeping a larger than stoichiometric molybdate to lacunary polyoxometalates ratio during the synthesis and the recrystallization in fairly acidic medium. Purity of the isolated product was checked by elemental analysis, electrochemistry, IR spectroscopy, UV–Vis spectroscopy and 183W NMR spectroscopy. Comparison of the physical characteristics of α-K6[As2W12Mo6O62] · 12H2O with the corresponding ones of its known phosphorus analogue, α-K6[P2W12Mo6O62] · 14H2O, confirms that the two complexes have the same structure. The expected positive potential shift of the first several voltammetric waves linked with the presence of As instead of P as the central heteroatom in these molecules was observed. The behaviours of α-K6[As2W12Mo6O62] · 12H2O and α-K6[P2W12Mo6O62] · 14H2O in the electrocatalytic reduction of nitrous acid and nitrogen monoxide were studied and compared with each other and with the activity of α-K6[As2W18O62] · 14H2O.