Electronic properties of polyoxometalates: a DFT study of alpha/beta-[XM(12)O(40)](n-) relative stability (M=W, Mo and X a main group element)

Keggin heteropolyanions [XM(12)O(40)](n-) have various isomeric structures, alpha and beta being the most common. Conventionally, the alpha structure appears to be the most stable, but calculations carried out at the DFT level for X = P(V), Si(IV), Al(III), As(V), Ge(IV), and Ga(III) and M = W(VI) and Mo(VI) show that this stability depends on several factors, particularly on the nature of the heteroatom (X) and the total charge of the cluster. In this paper, we apply the clathrate model to the Keggin molecule to carry out a fragment-interaction study to elucidate when and why the traditional relative stability of various isomers can be inverted. The fully oxidized anions that have inverted the traditional stability trend in this series are [AlW(12)O(40)](5-) and [GaW(12)O(40)](5-), both of which contain a third-group heteroatom and an overall charge of -5. beta-isomers are always more easily reduced than alpha-isomers. This experimental observation suggests that reduction favors the stability of beta-isomers and one of the most important results of this study is that the alpha/beta inversion is achieved in most cases after the second reduction. The alpha- and beta-isomers may have different properties because the energy of the LUMO, a symmetry-adapted d(xy)-metal orbital, is different.     

A study of thin surface layers by multilayer Mössbauer spectroscopy /MMS/

A stacking Mössbauer technique, MMS has been applied for studying thin surface layers. The surface layers formed on the⁵⁷Fe film in aqueous solutions of corrosion inhibitors, such as zinc phosphate and barium metaborate, and in distilled water was studied by this method. It has been found that the corrosion is much slower in the presence of zinc phosphate and barium metaborate. XPS analysis suggests the formation of a mixed iron zinc phosphate on the surface of the⁵⁷Fe film after corrosion in a zinc phosphate solution.     

Über die Reproduzierbarkeit der turbidimetrischen Bestimmung von Phosphorspuren mit Strychninmolybdostickstoff(V)säure

Microchimica Acta - Mit der turbidimetrischen Strychninnitrat-Methode für Phosphorspurenbestimmung nach der Version von Hegedüs und Dvorszky kann man nur dann ausgezeichnete...     

Radionuclide X-ray fluorescence determination of Cr, Fe, Cu, Zn and Pb in industrial wastewaters after preconcentration of determined elements

Radionuclide X-ray fluorescence analysis was used for the determination of Cr, Fe, Cu, Zn and Pb in industrial wastewaters (from surface treatment of metals and glasses) after precipitation of determined elements by 8-hydroxyquinoline.