We report Peacock–Weakley complexes, Na9[Ln(W5O18)2]∙35H2O, formed with Tm(III), 1, and Yb(III), 2. Their syntheses, physico-chemical characterizations, crystal structures, and magnetic properties are described. Ab initio calculations are also reported. These polyoxometalate (POM) complexes were obtained using original synthetic conditions where acidification was performed with a stoichiometric amount of nitric acid to an acidity of Z = ν(H+)/ν(WO42–) = 8/10 = 0.80. Both the Tm(III) and Yb(III) derivatives were found to exhibit field-induced slow relaxation of their magnetization likely controlled by Raman and Orbach relaxation processes. 1 is a rare example of a Tm(III)-based single-molecule magnet (SMM) and is a consequence of the oblate tetragonal anti-prismatic symmetry of the coordination sphere.
Conditions necessary for the formation of La(III)-containing polyoxotungstates in solutions of the system Na2WO4 – HNO3 – La(NO3)3 – H2O/Solvent (Solvent = acetone, acetonitrile, ethanol; 50/50 vol.% Н2О: Solvent ratio) acidified to acidity Z = ν(H+)/ν(WO42–) = 0.80 were elaborated. It was established that during salting out, the addition of an organic solvent leads to the crystallization of normal salts, Na9[La(W5O18)2]·nH2O (n = 32–35). Using FT-IR spectroscopy, it was shown that the anion [La(W5O18)2]9– in the composition of the isolated salts belongs to the Peacock–Weakley type of structure and the absence of solvent molecules in the composition of the crystalline product was established. Using the method of scanning electron microscopy, the single-phase nature of the synthesized salts was established (according to the uniform contrast of the surface of the samples during scanning in the backscattered electron mode and according to the results of energy dispersive X-ray microanalysis), and the grain sizes were determined (from 140–300 nm for the salt isolated from the H2O: acetone medium, to 300–450 nm for the salt isolated from the H2O: ethanol system). Microphotographs of powders of Na9[La(W5O18)2]·nH2O salts powders in characteristic X-ray emission do not show zones with different surface morphology, and demonstrate uniform distributions of Na, La, W, and O without segregation, which confirms the single–phase nature of the samples isolated from aqueous-organic solutions. The conducted research made it possible to expand the list of organic solvents that can be used for the synthesis of normal salts with a heteropoly anion with a Peacock–Weakley type of structure from aqueous-organic solutions. The use of acetonitrile and ethanol for Na9[La(W5O18)2 ]·nH2O isolating can be extended to the synthesis of salts with other lanthanide heteroatoms.
Определены различия в условиях синтеза гетерополисоединений Na 9 [Ce III (W 5 O 18) 2 ]•28H 2 O и Na 6 Н 2 [Ce IV (W 5 O 18) 2 ]•30H 2 O из подкисленного водного раствора вольфрамата натрия. Методом ИК-спектроскопии установлена принадлежность анионов в составе солей к структуре Пикока-Уикли и показано, что в случае присутствия Ce(IV) наблюдается смещение (10-30 см-1) как деформационных, так и валентных мостиковых колебаний в структуре [Се IV (W 5 O 18) 2 ] 8по сравнению с [Се III (W 5 O 18) 2 ] 9-. Методом сканирующей электронной микроскопии установлена однофазность полученных солей и показаны различия в микроморфологии и размере частиц Na 6 H 2 [Ce IV (W 5 O 18) 2 ]•30H 2 O (d = 200-400 нм) и Na 9 [Се III (W 5 O 18) 2 ]•28H 2 О (d < 2.5 мкм).
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