Un nouveau dimère hétéropolytungstique [(SiW10O37)2Fe4(OH)4]12– formé par la réunion par deux ponts hydroxo de deux unités α-SiW10Fe2O39. Synthèse et structure de son sel de rubidium

Abstract

Abstract A novel heteropolytungstate dimer [(SiW10O37)2Fe4(OH)4]12– formed by connecting two α-SiW10Fe2O39 units by two hydroxo bridges. Synthesis and crystal structure of its rubidium salt. The heteropolyanion [(SiW10O37)2Fe4(OH)4]12– is obtained by reaction of iron(III) nitrate on potassium undecatungstosilicate. This reaction leads, in a first step, to a ferri-undecatungstosilicate which dimerizes in neutral medium; in a second step, substitution of an iron for a tungsten atom occurs. The compound is isolated as a rubidium salt Rb12(SiW10O37)2Fe4(OH)4·28 H2O and characterized by elemental analysis, infrared spectroscopy and polarography. The novel polyoxoanion can be described as a dimer of Keggin ions. Two lacunary [α-SiW10O37]10– units, which accommodate two Fe3+ ions each, are linked through two bridging hydroxo groups. The locating of the hydroxo groups is done by the bond valence sum calculations. The title compound crystallizes in a monoclinic unit cell with lattice constants a=12.613(9), b=35.858(9), c=23.347(5) A, α=93.58(3)°, V=10 538(8) A3 and Z=4. The structure is solved by direct methods. The final reliability factors R and Rw are respectively equal to 0.0775 and 0.0870. © 2000 Academie des sciences / Editions scientifiques et medicales Elsevier SAS. ferritungstosilicate / heteropolyanion / polyoxometalate / crystal structure