Phosphotungstate species

For example, at a calcination temperature of 100 °C, the yield of epoxide was found to be only 10.3 %, whereas at 500 °C. the yield dramatically increased to over 88 %. However, at a calcincination temperature of 600 °C, the yield drops off suddenly. Work is still on-going as to the nature of the active species. However, solid state NMR, IR, and Raman all show that changes take place upon calcination which is not just the formation of layered tungstates. For example, a dimeric species appears to be stabilized by the alumina support when the phosphotungstic acid salt was immobilized. 

It is also possible to titrate biochemical species. Antibodies have been titrated with antigen, and enzyme-substrate mixtures have been titrated with appropriate coenzymes. Proteins are readily titrated with acid or base, or precipitated with phosphotungstic acid, yielding very informative thermometric titration curves [7, 8]. 

Each of the products whose synthesis is illustrated in Schemes 6.2 and 6.3 is a coloured cationic species. When the counteranion is chloride, the products are water-soluble and useful as basic (cationic) dyes for the eoloration of acrylic fibres. Precipitation of cationic dyes of these types from aqueous solution using large polymeric counteranions, notably phosphomolybdates, phosphotungstates and phos-phomolybdotungstates, leads to a range of highly insoluble red. 

Recently, however, formation of a red Cm(iv) complex in phosphotungstate solution was achieved by the use of peroxydisulfate as the oxidant [53], Kosyakov et al. [54] demonstrated that in such solutions the Cm(iv) is reduced much faster than can be accounted for by radiolytic effects, while Am(iv) in such solutions is much more stable, being reduced at a rate attributable to radiolytic effects alone. No value for the E° (Cm /Cm ) is known but from existing data it is substantially more positive than E° (Am /Am ) and probably about as positive as °(Pr /Pr ). The recent success of generating soluble carbonate solutions of Pr(iv) suggests that similar soluble Cm(iv) species may be prepared [55], All known Cm(iv) compounds are either fluorides or oxides, but a broader chemistry has been developed for Cm(iii). 

Electrochemical measurements have been made of actinide ions in complexed aqueous media, especially carbonate-bicarbonate systems [66-68]. Such measurements are particularly useful in establishing the actinide oxidation states and species present in natural water and biological systems. Complexes such as fluoride, chloride, carbonate, and phosphotungstate are stronger with tetravalent than with trivalent cations, so they significantly stabilize the higher oxidation state. 

Two types of ammonium cations in ammonium 12-phosphotungstate hydrate, (NH4)3PWi2O40 H20, have been detected by Chernyak et al. ° by the use of and MAS NMR spectroscopy one type of ammonium cations is in the bulk of crystallites, while the other type is on their surface. Vhi4n of 57 Hz and Vhisn of 78 Hz have been measured for the first type of species and Vhi4n of 51 Hz and Vhisn of 75 Hz for the latter one. 

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