SYNTHESIS, FTIR SPECTROSCOPY, AND SURFACE MICROMORPHOLOGY OF Се(III) AND Ce(IV)-CONTAINING HETEROPOLY TUNGSTATES WITH PEACOCK–WEAKLEY STRUCTURE OF ANION

Abstract

The conditions for the synthesis of sodium heteropoly decatungstoceriate(III) Na9[CeIII(W5O18)2]·28H2O from the aqueous solution of sodium tungstate acidified to Z=ν(H+)/ν(WO42–)=0.80 with a ratio ν(Ce):ν(W)=1:10 and with acetone admixture were elaborated. The methods of chemical analysis, EDX, and FTIR spectroscopy were used to show that sodium-hydrogen heteropoly decatungstoceriate(IV) Na6H2[CeIV(W5O18)2]·30H2O was synthesized by self-assembly in solutions with mononuclear initial components (WO42– and Ce3+) with Z=0.80 and precipitated through slow H2O evaporation at room temperature. Nature of stretching and deformation vibrations in the tungsten-oxygen framework within FTIR spectra of air-dry samples of salts indicate to the presence of Peacock-Weakley heteropoly anions of 10th row in the composition of salts. In these anions, two lacunar tetradentate pentatungstate- anions [W5O18]6– are coordinated to Ce(III)- and Ce(IV)-heteroatoms, thus forming a coordination polyhedron in the shape of a square antiprism. Using FTIR spectroscopy it was shown that the presence of Ce(IV) results in the displacement (10–30 сm–1) of both deformational and stretching bridge vibrations in the structure of [CeIV(W5O18)2]8– if compared to [CeIII(W5O18)2]9–. The method of scanning electron microscopy was used to show that the grain size of Na6H2[CeIV(W5O18)2]·30H2O is within the range of 200–400nm, while the grain size of Na9[СеIII(W5O18)2]·28H2О makes up to 2.5μm. Homogeneity of the obtained samples was confirmed by the uniform contrast of the surface mode of backscattered electrons. On the micrographs of salts powder in characteristic X-ray emission there are no regions with different surface morphology, and there is an even distribution of Ce, Na, W, and O, without segregation and eliquation. These clearly point to the formation of single phase samples.

Keywords

• гетерополіаніон, вольфрамат, Церій, мікроморфологія, ІЧ- спектроскопія