Uranyl oxalate complexes. Part III. Preparation and crystal and molecular structure of ammonium diuranyl trioxalate

The crystal structure of the title compound has been determined from photographic and diffractometer data by the heavy-atom method. Crystals are monoclinic, space group P21/n, a= 9·46(2), b= 13·61(2), c= 6·12(1)Å, β= 92·7(1)°, Z= 2. 886 Reflections were refined to a final R of 0·113. The crystal contains NH4+ and [(UO2)2(C2O4)3]n2n– ions. In the latter, one oxalate group is ter- and one quadri-dentate, giving double chains parallel to c. Mean U–O distances are 1·77 (uranyl) and 2·38 Å(to oxalate). The structures and bonding of oxalato- and other complexes of UO2+ are discussed.