SYNTHESIS OF SODIUM HETEROPOLY DECATUNGSTOEUROPATE(III) WITH PLATE-LIKE SURFACE MICROMORPHOLOGY

Abstract

In order to develop an express procedure for the synthesis of the Eu(III)-containing heteropoly compound Na9[Eu(W5O18)2]·35H2O, a study of the interaction in an aqueous solution of the Na2WO4 – HNO3 – Eu(NO3)3 – H2O system acidified to an acidity of Z = ν(H+)/ν(WO42–) = 0.80 was carried. A procedure for obtaining a single-phase sample of Na9[Eu(W5O18)2]·35H2O is proposed, which is performed by a simple technique in a short time, which does not exceed 5 days from the addition of reactants to obtaining the target product with a yield of more than 90%. It was established that during salting out, the addition of an organic solvent (propan-2-one) results in the crystallization of Na9[Eu(W5O18)2]·35H2O normal salt with plate-like surface micromorphology. The set of oscillations characteristic for the heteropoly tungstate anion with the Peacock–Weakley type of structure, [Eu(W5O18)2]9–, was established by the methods of FT-IR spectroscopy and FT-Raman spectroscopy. By the method of FT-IR spectroscopy the absence of organic solvent molecules (propan-2-one) in the composition of the crystalline product was established. The revealed set of vibrations in the FT-IR and Raman spectra of the isolated salt (the most intense valence vibrations at 710, 797, 849, and 935 cm-1 in the FT-IR spectrum; intense bands in the region of 930–980 cm-1 in the Raman spectrum) is characteristic of the site group of the heteropoly anion [Ln(W5O18)2]9– (Ln = La–Lu) and is identical to the FT-IR and Raman spectra of salts, the crystal structure of which has been reliably established by single crystal X-ray diffraction analysis. By the method of scanning electron microscopy, it was shown that the grain size of Na9[Eu(W5O18)2]·35H2O powder is up to 500 nm. The single phase of the salt was confirmed by the uniform surface contrast in the backscattered electron imaging (BEI) mode and by the uniform distribution of Eu, Na, W, and O during the scanning of the surface in the characteristic X-ray radiation.