Uranyl pyrophosphate

Uranyl pyrophosphate, (U03)2P207, is formed as a precipitate when a solution of sodium metaphosphate is poured into a hot solution of uranyl nitrate. The tetrahydrate, (U02)2P20,.4H20, is precipitated in yellow microcrystals by double decomposition of sodium pyrophosjihate and uranyl nitrate. The hydrate loses water and yields the anhydrous salt at 120° C. Uranyl pyrojohosphate is insoluble in water, alcohol, or ether but it dissolves in excess of sodium pyrophosphate solution (see below), and also in dilute nitric acid. 

Gravimetric Estimation.—Many methods for the quantitative determination of uranium have been described, but the follo%ving appear to be the most trustworthy (1) precipitation with ammonia as ammonium diuranate, and ignition to urano-uranie oxide (2) precipitation of uranyl ammonium phosphate by means of ammonium phosphate in presence of ammonium acetate, and ignition of the precipitate to uranyl pyrophosphate and (8) precipitation as uranyl sulphide by means of ammonium sulphide, and ignition to urano-uranie oxide. 

The phosphate method is difficult owing to the fineness of the precipitate, and a complete sejjaration from the alkali metals is almost impossible. After boiling for about fifteen minutes, the precipitate becomes crystaUine and is more easily filtered. Precautions must be taken in cooling and weighing the ignited uranyl pyrophosphate since it rapidly absorbs moisture. 

The structure of CS2UO2P2O7 consists of uranyl square bipyramids that share equatorial vertices with pyrophosphate groups to form an open sheet (Fig. 47). The Cs atoms are centered below the cavities in the sheets and occupy the interlayer region [181]. The uranyl pyrophosphate sheet in CS2UO2P2O7 can be compared to the uranyl phosphate sheet found in autunite-type compounds (Fig. 28) the pyrophosphate group of the [(U02)(P207)] sheet occupies the same position as the single phosphate tetrahedron in the autunite-type sheet, [(U02)(P04)]. 

Uranium Monophosphide, UP. —Uranyl hypophospbite on strongly heating leaves a residue consisting of a mixture of uranous pyrophosphate, uranous metaphosphate, and uranium monophospMde, hydrogen alone escaping. 

All of the solvents extract uranliun from aqueous solution In proportion to the square of the solvent concentration (in benzene). However, not all solutions of the solvent In benzene and saturated In uranyl nitrate give mole ratios of solvent to uranium of 2 1. For the two dlphosphanates and one pyrophosphate studied the mole ratios were 1 1. This may be Indicative of chelation or polymer formation. The mole ratio in trlphenyl phosphate was 22 1. This Is probably the result of the solvent being unable to displace water from the coordination sphere of the uranyl lon. iSS,... 

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