Hans-Joachim Lunk

The new phase Ba0.167Fe0.083WO3+0.29 : a product of the thermal degradation of the heteropoly KEGGIN compound Ba2H[α-FeO4W12O36].26H2O

Abstract The thermal degradation of the polyoxometallate Ba 2 H[α-FeO 4 W 12 O 36 ] · 26H 2 O was investigated by means of X-ray heating patterns, thermal analysis (TG, DTG, DTA, DSC) and spectroscopic methods (IR, ESR, Mossbauer). The formation of the new hexagonal phase Ba 0.167 Fe 0.083 WO 3+0.29 ( a = 7.320, c = 7.389 A) can be observed. The phase is stable at room temperature. Its structure is related to hexagonal tungsten bronzes but differs from them due to the presence of oxygen in addition to barium and iron along the hexagonal channels. The high positive charge of the cations leads to the maximum contraction of the cell parameter c .

Solid state reactions of chromium(III)-substituted heteropoly tungstates with chromium(III) ammine cations☆

The reaction of chromium ammine complexes with chromium-substituted Keggin anions in aqueous solution forms insoluble salts which were then heated to temperatures of 240 and 350°C. The thermal behaviour of the ammine complexes is dominated by a strong exothermic reaction which is interpreted as a linking reaction (condensation) between chromium from the complex ammine cation and the heteropolyanion. Thermal treatment of the title compounds yields products that are soluble in water and could be crystallized as potassium salts in several cases. A chromium-caped Keggin anion is the proposed structure.