Synthesis conditions and some properties of neptunium (IV) oxalates in which C/sub 2/O/sub 4//Np = 2. 5

A study was made of the formation of neptunium oxalates of the type M/sub 2/Np/sub 2//centered dot/(C/sub 2/O/sub 4/)/sub 5//centered dot/(7-9)H/sub 2/O, where M = H, NH/sub 4/, Na, K. It was found that the acid oxalate may crystallize out together with the normal hexahydrate of neptunium (IV) oxalate over a wide range of conditions, but it may be obtained in almost pure form when the initial neptunium concentration is (1-2)/centered dot/10/sup /minus/2/ M and the nitric acid concentration is above 3 M. Other salts are formed in the same conditions as the analogous thorium and uranium (IV) compounds. An analysis of the diffractograms shows the structural similarity of the acid oxalate to other salts, especially the ammonium salt. The IR spectra of the acid oxalate did not include absorption bands which could be ascribed to the bioxalate ion. The results indicate that the formula for this oxalate should be written in the form (H/sub 3/O)/sub 2/Np/sub 2/(C/sub 2/O/sub 4/)/sub 5//centered dot/7H/sub 2/O.