Darstellung und Strukturuntersuchung von Polywolframaten Ein Beitrag zur Aufklärung des Parawolframations A

J o a c h i m F u c h s u n d E r n s t P e t e r F l i n d t Institut für Anorganische Chemie der Freien Universität Berlin Z . Naturforsch. 34b, 412 -422 (1979); eingegangen am 28. November 1978 Properties, X r a y , Heptatungstate , Paratungstate A , Metatungstate Polytungstates are obtained b y the reaction of hydrated tungsten (VI) oxide with bases or salts after occasional addition of organic solvents. Wi th liquid ammonia the as ye t unknown ditungstate, (NH4)2W2Ü7, is produced. Its I R spectrum has f ew absorption bands suggesting a very simple constitution. Piperidine yields 5 compounds according to varied experimental conditions, which all exhibit approximately paratungstate composi tions but different crystal habits, lattice parameters, solubility and I R spectra. Structure determinations indicate that t w o o f these compounds are heptatungstates, the anion of which, W7024 6 , has the same structure as the heptamolybdate ion, Mo70246~. F r o m a comparison of their R a m a n spectra with the spectrum of a freshly acidified sodium tungstate solution (designated as Paratungstate A ) it m a y be concluded that the heptatungstate ion is the predominant species in such a solution. The anion structure of the previously described t r ibuty lammonium(5 :24 ) : tungstate [ (GiHg^NHJsHaW^C^o was elucidated b y X r a y methods . Here the tungsten atoms show the same arrangement as in the a-dodecatungstatophosphate ion (Keggin structure).