Uranyl Hypophosphite, UO₂(H₂PO₂)₂

Uranyl Hypophosphite, UO₂(H₂PO₂)₂.H₂O, is obtained as a yellow crystalline powder when freshly precipitated ammonium di-uranate is digested with aqueous hypophosphorous acid. It is insoluble in water, soluble in acids. On heating, it loses water between 100° and 200° C., and at higher temperatures decomposes with explosive violence, yielding hydrogen and a residue containing the monophosphide as described above. The anhydrous salt, UO₂(H₂PO₂)₂, may be prepared by agitating solutions of 1 molecular proportion of uranyl nitrate and 4 molecular proportions of sodium hypophosphite. It separates in yellow microcrystalline prisms, insoluble in water, but readily soluble in excess of either reagent. A pale yellow trihydrate has also been obtained.

By the action of alkali hypophosphites on uranyl hypophosphites the following complex salts have been prepared:

Na[(UO₂)(H₂PO₂)₃].3.5H₂O, and 5H₂O;
Na[(UO₂)₂(H₂PO₂)₅].4.5H₂O, and 6H₂O;
K[(UO₂)₂(H₂PO₂)₅];
NH₄[(UO₂)₂(H₂PO₂)₅].