Darstellung und Strukturuntersuchung von Polywolframaten Ein Beitrag zur Aufklärung des Parawolframations A / Preparation and Structure Investigation of Polytungstates A Contribution to the Paratungstate A Problem

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Abstract
Polytungstates are obtained by the reaction of hydrated tungsten (VI) oxide with bases or salts after occasional addition of organic solvents. With liquid ammonia the as yet unknown ditungstate, (NH4)2W2O7, is produced. Its IR spectrum has few absorption bands suggesting a very simple constitution. Piperidine yields 5 compounds according to varied experimental conditions, which all exhibit approximately paratungstate compositions but different crystal habits, lattice parameters, solubility and IR spectra. Structure determinations indicate that two of these compounds are heptatungstates, the anion of which, W7O24 6-, has the same structure as the heptamolybdate ion, Mo7O24 6-. From a comparison of their Raman spectra with the spectrum of a freshly acidified sodium tungstate solution (designated as Paratungstate A) it may be concluded that the heptatungstate ion is the predominant species in such a solution. The anion structure of the previously described tributylammonium(5:24):tungstate [(C4H9)3NH]5H3W12O40 was elucidated by X-ray methods. Here the tungsten atoms show the same arrangement as in the α-dodecatungstatophosphate ion (Keggin structure).

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