SYNTHESIS, FT–IR SPECTROSCOPY AND SURFACE MICROMORPHOLOGY OF Ho(III)–CONTAINING POLYOXOTUNGSTATES

Abstract

The formation of Ho(III)-containing polyoxotungstates in acidified to different acidity Z = ν(H+)/ν(WO42–) = 0.80, 1.17, 1.29, and 1.50 solutions of the Na2WO4 – HNO3 – Ho(NO3)3 – H2O system was studied. The conditions for the synthesis of Na9[Но(W5O18)2]·23H2O from the aqueous solution of sodium tungstate acidified to Z=0.80 and with acetone admixture were elaborated. The FT–IR spectroscopy was used to determine the belonging of anion [Ho(W5O18)2]9– in the synthesized compound to the Peacock–Weakley type of structure. By the method of scanning electron microscopy salt is proved to be single-phase, and its grain size is in the range 200-400 nm. The technique developed in this work for the preparation of sodium decatungstoholmiate(ІІІ) is new and differs in that it allows one to synthesize a normal salt, which can be used for the synthesis of other normal salts of sodium heteropoly decatungstolanthanidates(ІІІ). As a result of attempts to synthesize salts by the interaction of holmium(III) nitrate with aqueous solutions of sodium tungstate acidified to Z = 1.17 and 1.29, X-ray amorphous solids were obtained, which most likely are mixtures of paratungstate B and holmium heptatungstate. Using the methods of chemical analysis and FTIR spectroscopy, the conditions for the formation of a sodium-holmium double salt with lacunar undecatungstate anion, derived from Keggin structure Na2Ho2[Нo2(H2O)10W22O72(OH)2]·46H2O are established. Procedure for the synthesis of holmium(III) paratungstate B Ho10[W12O40(OH)2]3·54H2O by the exchange reaction of holmium(ІІІ) nitrate with sodium paratungstate B was elaborated, and by the method of scanning electron microscopy it is proved to be single–phase. It was found that the grain size of the sample is in the range 200–450 nm. The absence of sodium(I) ions in the composition of the synthesized salt was proved by atomic absorption spectroscopy and EDX. Microphotographs of the salt powders Na9[Но(W5O18)2]·23H2O and Ho10[W12O40(OH)2]3·54H2O in the characteristic X–ray radiation show no zones with different surface morphologies, and show uniform distribution of Na, Ho, W, O is observed without segregation, which confirms the single–phase nature of the products.

Keywords

• ізополіаніон
• гетерополіаніон
• аніон паравольфрамату б
• гольмій
• мікроморфологія поверхні