The solid-state structures of the [U-IV(NO3)(6)](2-) anions in the [n-Pr4N](2)[U(NO3)(6)] (1), [n-Bu4N](2)[U(NO3)(6)] (2). and [Ph4P](2)[U(NO3)(6)]center dot 4NCCH(3) (3) salts were determined using single-crystal X-ray diffraction. For the first time, a nondisordered structure of the hexanitratouranate(IV) dianion with a coordination number of 12 for the central U-IV atom was determined. Salts 1-3 were prepared in simple metathesis reactions and characterized using IR spectroscopy, C/H/N analysis, and single-crystal X-ray diffraction. Attempts to prepare a salt containing the [U-IV(ClO4)(6)](2-) anion using the analogous route resulted in the isolation of U(ClO4)(4)(NCCH3)(5) (4), which was characterized using single-crystal X-ray diffraction. Compound 4 is the first structurally characterized uranium(IV) perchlorate to be reported in the literature.