Hétéropolyanions de type Dawson. 2. Synthèses de polyoxotungstoarsénates lacunaires dérivant de l'octadécatungstodiarsénate. Étude structurale par RMN du tungstène-183 des octadéca(molybdotungstovanado)diarsénates apparentés

The di-, tri-, and hexavacant lacunary tungstoarsenates α-[HAs2W16O59]11−, α-[As2W15O56]12−, and α-[H2As2W12O48]12− were prepared by controlled alkaline degradation of the Dawson-type anion α-[As2W18O62]6−. The relationships between all these anions and the two α-[As2W17O61]10− isomers were established. The mixed saturated derivatives α-[As2VxW18−xO62](6+x)− (x = 1,2,3) and α-[As2MoxW18−xO62]6− (x = 1, 3) were obtained by refilling the lacunas with vanadium and molybdenum respectively. The new mixed anion α2-[As2Mo2W15O61]10− was used concurrently with α-[HAs2WI6O59]11− to obtain α-[As2Mo2W16O62]6−; in both cases minor parts of α-[As2MoxW18−xO62]6− (x = 1 and 3) were obtained simultaneously. All species have been characterized by polarography and by IR spectrometry. Proposed structures, based on the similarity of the redox properties and syntheses processes to those of the corresponding Dawson-type lacunary and mixed tungstophosphates, were given for all these species. The structures of the "saturated" tu...